Systematic Review on the Behaviour of Carbon and Stainless Steel Reinforcing Bars in Buildings Under High Temperatures

Abstract

Carbon and stainless steel reinforcing bar behaviour at high temperatures and subsequent cooling is central to fire safety for buildings. This systematic review examines the peer-reviewed literature between 2015 and 2024, concentrating on mechanical performance, microstructural transformation, and responses under various cooling conditions. Since experimental studies on some reinforcing steels in building construction are scarce, based on the selection criteria, they were selected on different standards. Austenitic stainless steels like show better thermal stability, here determined by their ability to preserve mechanical strength and ductility after exposure to fires, compared with carbon steel. Several studies indicate that rapid cooling, especially after exceeding critical transformation temperatures, can induce the formation of martensitic structures in carbon steel. These structures can increase toughness but often lead to reduced ductility and a more brittle mechanical response. These effects are particularly relevant in contexts where structural elements remain in service after a fire. The methodology adheres to PRISMA guidelines, providing transparency and an easily traced choice process. Key gaps in the post-fire performance of reinforcing bar in buildings are established by this review, with future directions in standard fire tests and an examination of effects from cooling under conditions that mimic building settings.

1. Introduction

Steel has long served as a cornerstone of construction, enabling the development of stronger and more efficient structures. Nonetheless, its vulnerability to high temperatures remains a critical, unresolved issue. Initially, steel profiles were favoured for their strength and durability [1], until the advent of reinforced concrete, which optimised structural design by combining the most advantageous properties of both materials [2]. Today, reinforced concrete stands as the most widely used construction material, valued for its load-bearing capacity and cost efficiency [3]. However, its reliability continues to depend on the reinforcing steel, whose behaviour under fire conditions poses a significant structural risk. Numerous fire events have exposed the susceptibility of steel to elevated temperatures, often leading to structural failures that highlight gaps in current regulations and fire prevention strategies [4].

Although stainless steel demonstrates superior thermal performance, its high cost renders it impractical for widespread use in large-scale construction projects [5,6]. Conversely, carbon steel remains the most used reinforcement material due to its excellent tensile strength and ductility [7,8]. However, its rapid mechanical degradation under fire conditions continues to compromise building safety [9]. Despite its benefits, the prohibitive cost of stainless steel restricts its application to niche scenarios [5,6,7,8,9,10]. This situation presents an urgent challenge: there is a pressing need to reassess existing standards, explore alternative materials and design strategies, and develop innovative solutions that can enhance structural resilience without sacrificing economic feasibility or public safety.

The development of standards such as Eurocode 2 and ACI 318 has been aimed at strengthening structural fire safety [11,12]. However, their application in practice remains inconsistent and, in many cases, insufficient, leaving many structures exposed to significant risks [13]. In response to this problem, new alloys and thermal exposure have been investigated with the aim of increasing the fire resistance of steel; however, their adoption has been limited, partly due to high costs and the absence of clear regulations promoting their use [14,15,16,17,18,19,20]. In addition, temperature sensors and intumescent coatings have been developed to mitigate the heating of steel during a fire, although these have not yet been established as an industry standard [21,22,23,24,25,26]. While corrosion represents a major structural challenge, the immediate impact of a fire is an even more critical threat. Recent research has evaluated post-fire cooling methods to determine whether steel can recover its mechanical properties after exposure to extreme heat; however, these advances have not yet been effectively incorporated into existing regulations, perpetuating a gap in structural safety [27,28,29,30,31,32].

Systematic reviews play a vital role in evaluating the quality of existing research, and the PRISMA methodology provides a standardised framework that ensures transparency and rigour in reporting findings [33,34,35,36]. Undertaking a comprehensive review of steels used in construction over the past decade is essential to deepening our understanding of their performance under high-temperature and fire conditions. Such analysis not only consolidates current knowledge but also opens avenues for future research and innovation in material design and structural safety. Recent studies have highlighted the importance of improving the safety and performance of reinforcing steels by analysing their chemical and mechanical properties in order to optimise their use in building structures exposed to fire conditions. This research seeks to answer the question of how carbon and stainless steels primarily used as reinforcement in concrete structures behave when subjected to high temperatures, particularly in fire scenarios. Although the focus is on reinforcing bars, the limited availability of studies addressing this exact application required the inclusion of structural steels with similar mechanical and chemical properties. This approach ensures that the selected literature remains technically relevant for understanding post-fire behaviour of passive reinforcements in buildings. The objective is to conduct a systematic review of the existing literature on cooling methods applied after fire exposure and their impact on the mechanical properties of these structural materials. To achieve this objective, this document is structured as follows: Section 2, detailing the search and study selection methods; Section 3, presenting the key findings from the reviewed studies; and, finally, the Section 4, where conclusions and recommendations for future research are drawn.

2. Materials and Methods

A comprehensive systematic review was undertaken within the domains of metallurgical engineering, construction, and structural design, with particular emphasis on the performance of passive carbon steel and stainless steel reinforcements. Adhering to the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses), this study was designed to provide a thorough and methodologically sound analysis. A carefully structured search strategy was implemented to identify high-impact journal articles published between 2015 and 2024, focusing on critical areas such as engineering, construction safety, and architecture. The methodological steps followed in this process are outlined below, building on approaches employed in comparable engineering studies [37].

2.1. Introduction to the Research and Resarch Question

To study the behaviour of carbon steel and stainless steel reinforcements under high temperatures, it is essential to understand how steel performs in extreme thermal conditions, ensuring safety while fostering innovation in material engineering. The initial questions guiding this study are as follows: How do passive steel reinforcements behave when exposed to high temperatures? And how can the fire resistance of these structural materials be improved? This research seeks to determine the global body of literature available on the behaviour of reinforcements in building fires, based on the following criteria: (a) year of publication, between 2015 and 2024; (b) country of origin, irrespective of location; (c) publications indexed in Scopus, Web of Science, and Google Scholar, and (d) written in English.

2.2. Search Strategies, Inclusion and Exclusion Criteria, and Article Selection Process

Based on the initial research question, a search strategy was established, and the databases for execution were defined. The selected databases were Scopus, Web of Science, and Google Scholar. The keywords and search terms, along with the search dates and the databases used, are detailed in

Table 1. Results of search strategies.

Keywords	Search Date	Database Used
A615, Structural steel, Quenched, Hypoeutectic steel, Strength, Ductility “A615” Or “Structural steel” Or “Quenched*” Or “Hypoeutectic steel” And “Strength*”And “Ductility”	7 June 2024	Google Scholar, Web of Science, Scopus
Fire, Structural steel, Quenched, Hypoeutectic steel, Strength, Ductility “Fire” And “Structural steel” Or “Quenched*” Or “Hypoeutectic steel” And “Strength*” And “Ductility”	17 June 2024 8 July 2024	Google Scholar, Web of Science, Scopus
A955, Structural stainless steel, Quenched, Hypoeutectic, strength, ductility “A955” Or “structural steel” Or “quenched*” Or “Hypoeutectic steel” And “strength*” And “ductility”	16 April 2025	Google Scholar, Web of Science, Scopus
“Stainless steel” AND “fire” AND “buildings” AND “concrete”	16 April 2025	Google Scholar, Web of Science, Scopus
“Carbon steel” AND “fire” AND “buildings” AND “concrete” and “rebars”	16 April 2025	Google Scholar, Web of Science, Scopus

.

A comprehensive literature search to explore the behaviour of carbon steel and stainless steel reinforcements under high temperatures was conducted from 2015 to June 2024. This time frame was selected to cover the last ten years of scientific production, allowing a contemporary overview of technological and methodological advances in the study of passive reinforcing steels exposed to different temperatures and cooling conditions, thus assessing the current state of knowledge and identifying recent gaps and challenges in structural fire safety, especially in the context of building construction. This also provides a basis for future research directions, including the development of new reinforcement strategies, using a combination of previously identified search terms: (a) ‘A615’, (b) ‘Fire’, (c) ‘A955’, (d) ‘Structural Steel’, (e) ‘Quenched’, (f) ‘Hypoeutectic steel’, (g) ‘Strength’, (h) ‘Ductility’, (i) ‘Stainless steel’, (j) ‘fire’, (k) ‘buildings’ (l) ‘concrete’, (m) ‘Carbon Steel’, (n) ‘rebars’, along with the operators ‘AND’ and ‘OR’. Additionally, the wildcard operator (*) was used to capture variations in plural forms, verb tenses, and synonyms of these terms. Three sequential searches were performed in each database to reduce potential publication biases, ensuring more comprehensive results and improving the scientific rigour. The first search was conducted in Google Scholar without the use of Boolean operators. The second search employed a more systematic approach, using the identified terms combined with Boolean operators [38].

Inclusion and exclusion criteria were established to ensure that only relevant and high-quality studies were included. The inclusion criteria were defined as follows:

-

Peer-reviewed articles.

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Studies published and indexed in journals from the mentioned databases.

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Studies written in English.

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Articles addressing the behaviour of steel under high temperatures and methods to improve structural performance in thermal incidents.

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Articles that specify the steel content or provide the properties of the steel as determined by the authors.

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Articles that specify fire scenarios in buildings or structures, even if chemical composition is not provided.

The exclusion criteria were as follows:

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Studies that do not specify the type of steel used.

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Studies not related to the behaviour of steel under high temperatures or to improvements in thermal incident resistance.

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Studies published in languages other than English.

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Studies that are not indexed.

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Studies that do not provide the chemical composition or type of steel.

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Studies involving high-carbon steel.

The study selection process began with an initial screening of the titles and abstracts of the identified articles to assess their relevance to the research question posed in this study. During this stage, articles that did not clearly demonstrate relevance were excluded. The articles that passed this initial filter were then reviewed in full to determine their actual alignment with the analysed topic. Studies that did not provide sufficient data for the research development or did not adequately address the research question were discarded. However, due to the limited availability of studies focusing exclusively on A615 and A955 steels, research on steels with similar properties and characteristics was included. This approach ensured that the collected information remained as representative and applicable as possible to the materials under study.

2.3. Data Extraction, Quality Assessment, and Synthesis

An Excel template was developed for the systematic extraction of data from the included studies. The extracted data included the following: (a) keywords, (b) Boolean operators, (c) search date, (d) database, (e) article title, (f) DOI, (g) authors, (h) year of publication, (i) country, (j) journal, (k) article type, (l) steel type, (m) steel classification, (n) chemical composition, (o) study objectives, (p) methodology, (q) heat treatments applied, (r) mechanical properties analysed, (s) results, (t) conclusions, (u) article strengths, (v) article weaknesses, (w) practical applications, (x) relevance to the research, (y) score, (z) Inclusion, and aa) exclusion. The quality of the included studies was assessed using the PRISMA 2020 checklist [39], which was adapted to meet the specific needs of this study while maintaining the quality standards required by the methodology.

2.4. Results, Discussion, and Conclusions

A PRISMA flow diagram was included to illustrate the study selection process, from the initial identification to the final inclusion. The key characteristics of the selected studies are presented in a detailed table. This section summarises the main findings related to the thermal behaviour of steel, as well as the improvement proposals identified. The results were discussed in the context of the research question, highlighting both their practical and theoretical implications. The strengths and limitations of this study were evaluated, including potential biases and methodological constraints. Recommendations for engineering practice and future research were also provided, based on the findings obtained.

3. Results

The systematic literature search resulted in a total of 5595 articles, of which 5038 were excluded after title and abstract screening, and 457 were duplicates (within the database and across searches). As a result, the eligibility of 100 articles was assessed. However, 51 articles were excluded due to the unavailability of the full text (the authors were contacted for access, but no response was received). An additional 21 articles were excluded based on the exclusion criteria previously outlined in the methodology (

Table 2. Articles excluded for this review and the reason of exclusion.

Reason of Exclusion	Articles (Year)
Studies that are not written in English.	Kostina, et al. (2023) [41]
Studies that do not provide chemical composition.	Maraveas, et al. (2017) [42]
	Chi and Peng (2017) [43]
	Aziz and Kodur (2016) [44]
	Jeong et al. (2020) [45]
	Zhou et al. (2022) [46]
Studies that do not specify the type of steel.	Huang, et al. (2023) [47]
	Chou et al. (2023) [48]
Studies that do not provide the temperature.	Koo (2021) [49]
	Kamil et al. (2019) [50]
	Ronanki et al. (2018) [51]
	Ismail (2020) [52]
Studies that are not indexed in SCOPUS, Web of Science, or Google Scholar journals.	Choi and Chung (2016) [53]
	Taufik et al. (2018) [54]
	Tang et al. (2015) [55]
	Pons et al. (2022) [56]
	Tseng et al. (2017) [57]
Medium-high carbon content.	Hussein et al. (2016) [58]
	Liu et al. (2020) [59]

). In total, 50 full-text articles were retrieved: 14 focused on carbon steel, 10 on stainless steel, and 4 studying carbon and stainless steels. These were deemed relevant for data analysis and extraction (Table 3, Table 4, Table 5, Table 6, Table 7 and Table 8). The flow diagram of the systematic search procedure is presented in Figure 1 [40].

In this systematic review, the articles were classified according to the type of steel that they analysed. Three main groups were identified: those focusing exclusively on carbon steel, those dealing only with stainless steel, and those studying both materials together. This classification facilitates a more precise understanding of how the scientific literature addresses the thermal and structural behaviour of each type of steel.

Of the studies reviewed, fourteen were devoted exclusively to the analysis of carbon steel. Within this group, 64% focused on structural applications, such as columns, beams, or other elements exposed to fire. All studies (100%) applied some form of thermal exposure, either by standardised curves such as ISO 834 [9], electric furnaces, or controlled heating followed by quenching in air or water. In addition, 28.57% included a detailed microstructural analysis, with emphasis on transformations such as ferrite, pearlite, or martensite, which are fundamental to understand how the material degrades after exposure to high temperatures. Overall, 64.29% of these papers combined structural analysis with fire exposure, reflecting a strong interest in understanding the post-fire performance of carbon steel in building contexts.

As for stainless steel, ten articles were identified that focused exclusively on its study. Of these, 56% dealt with structural applications, mainly in mixed concrete and stainless steel systems. The majority (89%) subjected the material through direct exposure to fire, heating ramps or cooling studies. However, none of these works analysed the microstructure of the steel, which represents an important limitation, given that the mechanical behaviour of this type of steel is highly dependent on its phase (such as austenitic or duplex). Only 45% of these studies combined thermal exposures with structural applications.

Finally, four papers simultaneously investigated the thermal and mechanical behaviour of carbon steel and stainless steel. Although these papers are valuable for direct comparisons between the two materials, only 25% addressed their use in structural applications. All the studies applied thermal exposures, but none included detailed microstructure analysis. Moreover, only 25% of them combined thermal and structural aspects in their approach.

The geographical distribution of the studies included in this review (Figure 2) shows a significant concentration in Asian and European countries, highlighting a clear international trend in structural steel research. For carbon steel, the articles originate mainly from China, the United States, and Bangladesh, with additional contributions from countries such as Pakistan, Switzerland, Turkey, and Poland, as well as cross-national collaborations. In this context, China stands out for its high number of publications, which is consistent with its leadership in production, consumption, and technological development in the construction sector. On the other hand, research focused on stainless steel shows a more dispersed distribution, with a strong presence of the UK, Portugal, Switzerland, and Belgium, both in individual studies and in collaborations with countries such as Finland and Spain. This geographical diversification suggests a growing European interest in the analysis of the thermal and structural behaviour of stainless steel, especially in design scenarios with fire resistance requirements. It is worth noting that nations such as China, Spain, and the UK are involved in studies relating to both types of steel, which is evidence of their involvement in comparative lines of research. This dual presence is particularly relevant for the development of design approaches that integrate the specific thermal and mechanical properties of each material, favouring more efficient and safer building solutions.

3.1. Characteristics of the Steels Analysed

Table 3 and Table 4 below summarise the chemical composition of the carbon and stainless steels, respectively, that are studied in the selected references. These tables highlight the key elements present in each type of steel, allowing for a comparative analysis of their compositions and properties. Table 3 shows the percentages of carbon, manganese, silicon, and other elements in carbon steels, while Table 4 summarises the contents of chromium, nickel, and other key components in stainless steels. This analysis is crucial for understanding how variations in chemical composition influence the mechanical properties, corrosion resistance, and thermal stability of each type of steel.

Table 3. Characteristics of the analysed carbon steel.

Author (Year)	Steel Classification	Chemical Composition
Yang et al. (2021) [60]	EN 10080 [61]; UNE 36068:2011 [62] B500A; ASTM A615 Grade 60 [63] EN 10025-2 [64] S235JR ASTM A36/A36M [65]	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.80%, P: ≤0.045%, S: ≤0.045%, Cu: ≤0.5% C: ≤0.22%, Mn: ≤1.4%, Si: ≤0.35%, P: ≤0.045%, S: ≤0.045%
Rafi et al. (2018) [66]	EN 10080; UNE 36068:2011 B500A ASTM A615 Grade 60 EN 10080 UNE 36065:2011 B500B ASTM A615 Grade 75	C: 0.188%, Mn: 0.664%, Cr: 0.381%, P: 0.020% C: 0.190%, Mn: 0.697%, Cr: 0.125%, P: 0.035%
Quiel et al. (2020) [67]	EN 10080; UNE 36068:2011 B500A ASTM A615 Grade 420/520/690 EN 10080 UNE 36065:2011 B500B/C ASTM A706 Grade 420/500 [68] B500B/B500C	C: 0.19%, Mn: 1.05%, P: 0.015%, S: 0.015%, Si: 0.15%, Cu: 0.45%, Ni: 0.10%, Cr: 0.10%, Mo: 0.03%, Sn: 0.005%, V: 0.02% C: 0.17%, Mn: 1.10%, P: 0.017%, S: 0.015%, Si: 0.18%, Cu: 0.45%, Ni: 0.15%, Cr: 0.18%, Mo: 0.05%, Sn: 0.01%, V: 0.03% C: 0.18%, Mn: 1.30%, P: 0.020%, S: 0.017%, Si: 0.22%, Cu: 0.47%, Ni: 0.20%, Cr: 0.30%, Mo: 0.06%, Sn: 0.015%, V: 0.04%, C: 0.14%, Mn: 1.10%, P: 0.015%, S: 0.015%, Si: 0.25%, Cu: 0.40%, Ni: 0.13%, Cr: 0.25%, Mo: 0.07%, Sn: 0.01%, V: 0.02% C: 0.13%, Mn: 1.45%, P: 0.018%, S: 0.017%, Si: 0.30%, Cu: 0.40%, Ni: 0.17%, Cr: 0.35%, Mo: 0.09%, Sn: 0.015%, V: 0.03%
Tariq et al. (2024) [69]	EN 10080; UNE 36065:2011 [70] B500C ASTM A706 Grade 550	C: 0.25%, S: 0.035%, P: 0.035%, Ceq: 0.40%, N:120 PPM
Li et al. (2021) [71]	EN 10080; UNE 36068:2011 B500C ASTM A706 Grade 60	C: ≤0.30%, Mn: 0.50–1.50%, Si: ≤0.50%, P: ≤0.035%, S: ≤0.045%, Ceq: ≤0.55
Sobhan et al. (2021) [72]	EN 10080; UNE 36068:2011 B400B ASTM A615 Grade 40	C: 0.23–0.25%, Mn: 0.60–1.30%, Si: 0.40–0.80%, P: ≤0.045%, S: ≤0.045%, Ceq: ~0.50
Ruan et al. (2015) [73]	EN 10080; UNE 36068:2011 B500A ASTM A615 Grade 60	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52
Cadoni et al. (2021) [74]	EN 10080; UNE 36065:2011 B500A ASTM A615 Grade 75	C: ≤0.24%, Mn: ≤1.65, P: ≤0.05, S: ≤0.05%, Ceq: ≤0.52
Chousidis et al. (2023) [75]	EN 10080; UNE 36065:2011 B500C ASTM A706 Grade 550	C: 0.24%, S: 0.055%, P: 0.055%, N: 0.014%, Cu: 0.650%, Ceq: 0.520%
Shahriar et al. (2018) [76]	EN 10080; UNE 36065:2011 B500B ASTM A615 Grade 60 ASTM A706 Grade 60 B500B/C	C: 0.24%, Si: 0.21%, Mn: 0.81%, P: 0.026%, S: 0.021%, Cr: 0.011%, Mo: 0.002%, Ni: 0.004%, Al: 0.001% C: 0.21%, Si: 0.18%, Mn: 0.70%, P: 0.011%, S: 0.020%, Cr: 0.077%, Mo: 0.010%, Ni: 0.044%, Al: 0.001%
Xu et al. (2023) [77]	EN 10080; UNE 36068:2011 B500B ASTM A615 Grade 65 EN 10025-2S235JR ASTM A36	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.80%, P: ≤0.045%, S: ≤0.045%, Cu: 0.8%, Ceq: ≤0.50 C: ≤0.22%, Mn: ≤1.4%, Si: ≤0.35%, P: ≤0.045%, S: ≤0.045%
Kültür et al. (2022) [78]	EN 10080; UNE 36065:2011 B500B ASTM A706 Grade 60 UNE-EN 10025-2A S235JR ASTM A36	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.80%, P: ≤0.035%, S: ≤0.035%, N: ≤0.012%, Ceq: ≤0.50, C: ≤0.17%, Mn: ≤1.40%, S: ≤0.035%, P: ≤0.035%
Abbas et al. (2023) [79]	EN 10080; UNE 36068:2011 B500B/C ASTM A706 Grade 60 ASTM A615 Grade 60	C: 0.25%, Mn: 1.28%, Si: 0.33%, S: 0.03%, P: 0.042%, Cr: 0.13%, Mo: 0.016%, Ni: 0.11%, Cu: 0.16%, Co: 0.012%, B: 0.005%, Ti: 0.004%, Pb: 0.019%, Bi: 0.0009%, V: 0.011%, Nb: 0.006%, Al: 0.008%, W: 0.002%, Sn: 0.024% C: 0.27%, Mn: 1.25%, Si: 0.30%, S: 0.026%, P: 0.041%, Cr: 0.10%, Mo: 0.018%, Ni: 0.12%, Cu: 0.16%, Co: 0.015%, B: 0.004%, Ti: 0.004%, Pb: 0.031%, Bi: 0.002%, V: 0.025%, Nb: 0.004%, Al: 0.012%, W: 0.042%, Sn: 0.023% C: 0.30%, Mn: 1.26%, Si: 0.29%, S: 0.02%, P: 0.035%, Cr: 0.092%, Mo: 0.007%, Ni: 0.088%, Cu: 0.17%, Co: 0.016%, B: 0.003%, Ti:0.003%, Pb: 0.02%, Bi: 0.003%, V: 0.012%, Nb: 0.003%, Al: 0.009%, W: 0.003%, Sn: 0.08%
Hager et al. (2021) [80]	EN 10080; UNE 36065:2011 B500B ASTM A615 Grade 75	C: 0.21%, Mn: 0.8%, Si: 0.15%, N: 0.009%, S: 0.030%, Ni: 0.12%, Cu: 0.28%, Ceq: 0.39%
Albero et al. (2024) [81]	EN 10080:2011 B500B ASTM A615 Gr. 75	C: ≤0.24%, Mn: ≤1.65, P: ≤0.05, S: ≤0.05%, Ceq: ≤0.52
Hua et al. (2022) [82]	EN 10080:2011; UNE 36068:2011 B500B/C ASTM A615 Gr. 60	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52
Wu et al. (2023) [83]	EN 10080:2011; UNE 36068:2011 B500B/C ASTM A615 Gr. 60	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52
Rehman et al. (2022) [84]	EN 10080:2011; UNE 36068:20 B500B; ASTM A706 Gr. 60	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Ceq: ≤0.51

Table 3. Characteristics of the analysed carbon steel.

Author (Year)	Steel Classification	Chemical Composition
Yang et al. (2021) [60]	EN 10080 [61]; UNE 36068:2011 [62] B500A; ASTM A615 Grade 60 [63] EN 10025-2 [64] S235JR ASTM A36/A36M [65]	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.80%, P: ≤0.045%, S: ≤0.045%, Cu: ≤0.5% C: ≤0.22%, Mn: ≤1.4%, Si: ≤0.35%, P: ≤0.045%, S: ≤0.045%
Rafi et al. (2018) [66]	EN 10080; UNE 36068:2011 B500A ASTM A615 Grade 60 EN 10080 UNE 36065:2011 B500B ASTM A615 Grade 75	C: 0.188%, Mn: 0.664%, Cr: 0.381%, P: 0.020% C: 0.190%, Mn: 0.697%, Cr: 0.125%, P: 0.035%
Quiel et al. (2020) [67]	EN 10080; UNE 36068:2011 B500A ASTM A615 Grade 420/520/690 EN 10080 UNE 36065:2011 B500B/C ASTM A706 Grade 420/500 [68] B500B/B500C	C: 0.19%, Mn: 1.05%, P: 0.015%, S: 0.015%, Si: 0.15%, Cu: 0.45%, Ni: 0.10%, Cr: 0.10%, Mo: 0.03%, Sn: 0.005%, V: 0.02% C: 0.17%, Mn: 1.10%, P: 0.017%, S: 0.015%, Si: 0.18%, Cu: 0.45%, Ni: 0.15%, Cr: 0.18%, Mo: 0.05%, Sn: 0.01%, V: 0.03% C: 0.18%, Mn: 1.30%, P: 0.020%, S: 0.017%, Si: 0.22%, Cu: 0.47%, Ni: 0.20%, Cr: 0.30%, Mo: 0.06%, Sn: 0.015%, V: 0.04%, C: 0.14%, Mn: 1.10%, P: 0.015%, S: 0.015%, Si: 0.25%, Cu: 0.40%, Ni: 0.13%, Cr: 0.25%, Mo: 0.07%, Sn: 0.01%, V: 0.02% C: 0.13%, Mn: 1.45%, P: 0.018%, S: 0.017%, Si: 0.30%, Cu: 0.40%, Ni: 0.17%, Cr: 0.35%, Mo: 0.09%, Sn: 0.015%, V: 0.03%
Tariq et al. (2024) [69]	EN 10080; UNE 36065:2011 [70] B500C ASTM A706 Grade 550	C: 0.25%, S: 0.035%, P: 0.035%, Ceq: 0.40%, N:120 PPM
Li et al. (2021) [71]	EN 10080; UNE 36068:2011 B500C ASTM A706 Grade 60	C: ≤0.30%, Mn: 0.50–1.50%, Si: ≤0.50%, P: ≤0.035%, S: ≤0.045%, Ceq: ≤0.55
Sobhan et al. (2021) [72]	EN 10080; UNE 36068:2011 B400B ASTM A615 Grade 40	C: 0.23–0.25%, Mn: 0.60–1.30%, Si: 0.40–0.80%, P: ≤0.045%, S: ≤0.045%, Ceq: ~0.50
Ruan et al. (2015) [73]	EN 10080; UNE 36068:2011 B500A ASTM A615 Grade 60	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52
Cadoni et al. (2021) [74]	EN 10080; UNE 36065:2011 B500A ASTM A615 Grade 75	C: ≤0.24%, Mn: ≤1.65, P: ≤0.05, S: ≤0.05%, Ceq: ≤0.52
Chousidis et al. (2023) [75]	EN 10080; UNE 36065:2011 B500C ASTM A706 Grade 550	C: 0.24%, S: 0.055%, P: 0.055%, N: 0.014%, Cu: 0.650%, Ceq: 0.520%
Shahriar et al. (2018) [76]	EN 10080; UNE 36065:2011 B500B ASTM A615 Grade 60 ASTM A706 Grade 60 B500B/C	C: 0.24%, Si: 0.21%, Mn: 0.81%, P: 0.026%, S: 0.021%, Cr: 0.011%, Mo: 0.002%, Ni: 0.004%, Al: 0.001% C: 0.21%, Si: 0.18%, Mn: 0.70%, P: 0.011%, S: 0.020%, Cr: 0.077%, Mo: 0.010%, Ni: 0.044%, Al: 0.001%
Xu et al. (2023) [77]	EN 10080; UNE 36068:2011 B500B ASTM A615 Grade 65 EN 10025-2S235JR ASTM A36	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.80%, P: ≤0.045%, S: ≤0.045%, Cu: 0.8%, Ceq: ≤0.50 C: ≤0.22%, Mn: ≤1.4%, Si: ≤0.35%, P: ≤0.045%, S: ≤0.045%
Kültür et al. (2022) [78]	EN 10080; UNE 36065:2011 B500B ASTM A706 Grade 60 UNE-EN 10025-2A S235JR ASTM A36	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.80%, P: ≤0.035%, S: ≤0.035%, N: ≤0.012%, Ceq: ≤0.50, C: ≤0.17%, Mn: ≤1.40%, S: ≤0.035%, P: ≤0.035%
Abbas et al. (2023) [79]	EN 10080; UNE 36068:2011 B500B/C ASTM A706 Grade 60 ASTM A615 Grade 60	C: 0.25%, Mn: 1.28%, Si: 0.33%, S: 0.03%, P: 0.042%, Cr: 0.13%, Mo: 0.016%, Ni: 0.11%, Cu: 0.16%, Co: 0.012%, B: 0.005%, Ti: 0.004%, Pb: 0.019%, Bi: 0.0009%, V: 0.011%, Nb: 0.006%, Al: 0.008%, W: 0.002%, Sn: 0.024% C: 0.27%, Mn: 1.25%, Si: 0.30%, S: 0.026%, P: 0.041%, Cr: 0.10%, Mo: 0.018%, Ni: 0.12%, Cu: 0.16%, Co: 0.015%, B: 0.004%, Ti: 0.004%, Pb: 0.031%, Bi: 0.002%, V: 0.025%, Nb: 0.004%, Al: 0.012%, W: 0.042%, Sn: 0.023% C: 0.30%, Mn: 1.26%, Si: 0.29%, S: 0.02%, P: 0.035%, Cr: 0.092%, Mo: 0.007%, Ni: 0.088%, Cu: 0.17%, Co: 0.016%, B: 0.003%, Ti:0.003%, Pb: 0.02%, Bi: 0.003%, V: 0.012%, Nb: 0.003%, Al: 0.009%, W: 0.003%, Sn: 0.08%
Hager et al. (2021) [80]	EN 10080; UNE 36065:2011 B500B ASTM A615 Grade 75	C: 0.21%, Mn: 0.8%, Si: 0.15%, N: 0.009%, S: 0.030%, Ni: 0.12%, Cu: 0.28%, Ceq: 0.39%
Albero et al. (2024) [81]	EN 10080:2011 B500B ASTM A615 Gr. 75	C: ≤0.24%, Mn: ≤1.65, P: ≤0.05, S: ≤0.05%, Ceq: ≤0.52
Hua et al. (2022) [82]	EN 10080:2011; UNE 36068:2011 B500B/C ASTM A615 Gr. 60	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52
Wu et al. (2023) [83]	EN 10080:2011; UNE 36068:2011 B500B/C ASTM A615 Gr. 60	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52
Rehman et al. (2022) [84]	EN 10080:2011; UNE 36068:20 B500B; ASTM A706 Gr. 60	C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Ceq: ≤0.51

Table 4. Characteristics of the analysed stainless steel.

Author (Year)	Steel Classification	Chemical Composition
Albero et al. (2024) [81]	UNE-EN 1992-1-2:2011 [11]; EN 10088-1:2024 [85] EN 1.4362 ASTM A955/A955M [86]	C: ≤0.24%, Mn: ≤1.65, P: ≤0.05, S: ≤0.05%, Ceq: ≤0.52 C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004, Co: 0.1%, Nb: 0.02%, N: 0.053%
Hua et al. (2022) [82]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52 C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Wu et al. (2023) [83]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52 C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Rehman et al. (2022) [84]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 EN 1.4401 EN 1.4436 ASTM A955/A955M	C: 0.032%, Mn: 1.72%, Si: 0.46%, S: 0.004%, P: 0.039%, Ni: 8.1%, Cr: 18.4%, Mo: 0.24%, N: 0.183% C: 0.023%, Mn: 1.438%, Si: 0.366%, S: 0.027%, Ni: 10.54%, Cr: 16.685%, Mo: 2.049%, N: 0.046%, Cu: 0.317%, Ti: 0.005% C: 0.028%, Mn: 1.36%, Si: 0.36%, S: 0.007%, P: 0.031%, Ni: 10.54%, Cr: 16.67%, Mo: 2.53%, N:0.061% C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Ceq: ≤0.51
Molkens et al. (2021) [87]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Arrais et al. (2022) [88]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Molkens et al. (2024) [89]	UNE-EN 1992-1-2:2011; EN 10088-1:2024; EN 1.4301; ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Cadoni and Forni (2019) [90]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Gao et al. (2018) [91]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301; EN 1.4401; ASTM A955/A955M	C: 0.023%, Mn: 1.22%, Si: 0.334%, S: 0.006%, P: 0.024%, Cr: 18.08%, Ni: 8.25% C: 0.022%, Mn: 1.12%, Si: 0.409%, S: 0.001%, P: 0.032%, Cr: 16.75%, Ni: 0.01%, Mo: 2.11%
Mehwish et al. (2023) [92]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301; EN 1.4362; ASTM A955/A955M	C: 0.032%, Mn: 1.72%V, Si: 0.46%, S: 0.004%, P: 0.039%, Ni: 8.1%, Cr: 18.4%, Mo: 0.24%, N: 0.183% C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Gardner et al. (2016) [93]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4307 EN 1.4311 EN 1.4162 EN 1.4362 ASTM A955/955M	C: ≤0.030%, Cr: 17.5–19.5%, Ni: 8.0–10.5%, Mn: ≤2.0%, Si: ≤1.0%, P: ≤0.045%, S: ≤0.015% C: ≤0.030%, Cr: 17.5–18.5%, Ni: 8.5–10.5%, N: 0.10–0.16%, Mn: ≤2.0%, Si: ≤1.0%, P: ≤0.045%, S: ≤0.015% C: ≤0.030%, Cr: 21–22%, Ni: 1.35–1.70%, Mn: 4.0–6.0%, N: 0.20–0.25%, Mo: ≤0.3%, Cu: 0.1–0.8% C: ≤0.030%, Cr: 21.5–24.5%, Ni: 3.0–5.5%, Mo: 0.05–0.6%, N: 0.05–0.20%, Mn: ≤2.5%, Si: ≤1.0%, Cu: ≤0.5%
Melo et al. (2022) [94]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4462 ASTM A955/955M	C: 0.017%, Cr: 22.76%, Mn: 1.57%, Ni: 4.64%, Mo: 3.21%, N: 0.171%, Si: 0.34%, Co: 0.17%, Ti: 0.004%
Melo et al. (2022) [95]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.04%, Si: 0.49%, Mn: 1.65%, Ni: 7.8%, Cr: 16.8%, Mo: 0.37%
Plioplys et al. (2024) [96]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.08%, Cr: 20%, Ni: 10.5%, Mn: 2.0%, Si: 1.0%, P: 0.045%, S: 0.03%, N: 0.10%

Table 4. Characteristics of the analysed stainless steel.

Author (Year)	Steel Classification	Chemical Composition
Albero et al. (2024) [81]	UNE-EN 1992-1-2:2011 [11]; EN 10088-1:2024 [85] EN 1.4362 ASTM A955/A955M [86]	C: ≤0.24%, Mn: ≤1.65, P: ≤0.05, S: ≤0.05%, Ceq: ≤0.52 C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004, Co: 0.1%, Nb: 0.02%, N: 0.053%
Hua et al. (2022) [82]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52 C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Wu et al. (2023) [83]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.25%, Mn: 1.6%, Si: 0.80, P: ≤0.045, S: ≤0.045%, Ceq: ≤0.52 C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Rehman et al. (2022) [84]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 EN 1.4401 EN 1.4436 ASTM A955/A955M	C: 0.032%, Mn: 1.72%, Si: 0.46%, S: 0.004%, P: 0.039%, Ni: 8.1%, Cr: 18.4%, Mo: 0.24%, N: 0.183% C: 0.023%, Mn: 1.438%, Si: 0.366%, S: 0.027%, Ni: 10.54%, Cr: 16.685%, Mo: 2.049%, N: 0.046%, Cu: 0.317%, Ti: 0.005% C: 0.028%, Mn: 1.36%, Si: 0.36%, S: 0.007%, P: 0.031%, Ni: 10.54%, Cr: 16.67%, Mo: 2.53%, N:0.061% C: ≤0.25%, Mn: ≤1.6%, Si: ≤0.50%, P: ≤0.05%, S: ≤0.05%, Ceq: ≤0.51
Molkens et al. (2021) [87]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Arrais et al. (2022) [88]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Molkens et al. (2024) [89]	UNE-EN 1992-1-2:2011; EN 10088-1:2024; EN 1.4301; ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Cadoni and Forni (2019) [90]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Gao et al. (2018) [91]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301; EN 1.4401; ASTM A955/A955M	C: 0.023%, Mn: 1.22%, Si: 0.334%, S: 0.006%, P: 0.024%, Cr: 18.08%, Ni: 8.25% C: 0.022%, Mn: 1.12%, Si: 0.409%, S: 0.001%, P: 0.032%, Cr: 16.75%, Ni: 0.01%, Mo: 2.11%
Mehwish et al. (2023) [92]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301; EN 1.4362; ASTM A955/A955M	C: 0.032%, Mn: 1.72%V, Si: 0.46%, S: 0.004%, P: 0.039%, Ni: 8.1%, Cr: 18.4%, Mo: 0.24%, N: 0.183% C: 0.025%, S: 0.003%, P: 0.032%, Si: 0.37%, Mn: 1.2%, Cr: 18.26%, Ni: 8.10%, Mo: 0.34%, Cu: 0.88%, Sn: 0.01%, Al: 0.004%, Co: 0.1%, Nb: 0.02%, N: 0.053%
Gardner et al. (2016) [93]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4307 EN 1.4311 EN 1.4162 EN 1.4362 ASTM A955/955M	C: ≤0.030%, Cr: 17.5–19.5%, Ni: 8.0–10.5%, Mn: ≤2.0%, Si: ≤1.0%, P: ≤0.045%, S: ≤0.015% C: ≤0.030%, Cr: 17.5–18.5%, Ni: 8.5–10.5%, N: 0.10–0.16%, Mn: ≤2.0%, Si: ≤1.0%, P: ≤0.045%, S: ≤0.015% C: ≤0.030%, Cr: 21–22%, Ni: 1.35–1.70%, Mn: 4.0–6.0%, N: 0.20–0.25%, Mo: ≤0.3%, Cu: 0.1–0.8% C: ≤0.030%, Cr: 21.5–24.5%, Ni: 3.0–5.5%, Mo: 0.05–0.6%, N: 0.05–0.20%, Mn: ≤2.5%, Si: ≤1.0%, Cu: ≤0.5%
Melo et al. (2022) [94]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4462 ASTM A955/955M	C: 0.017%, Cr: 22.76%, Mn: 1.57%, Ni: 4.64%, Mo: 3.21%, N: 0.171%, Si: 0.34%, Co: 0.17%, Ti: 0.004%
Melo et al. (2022) [95]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.04%, Si: 0.49%, Mn: 1.65%, Ni: 7.8%, Cr: 16.8%, Mo: 0.37%
Plioplys et al. (2024) [96]	UNE-EN 1992-1-2:2011; EN 10088-1:2024 EN 1.4301 ASTM A955/A955M	C: 0.08%, Cr: 20%, Ni: 10.5%, Mn: 2.0%, Si: 1.0%, P: 0.045%, S: 0.03%, N: 0.10%

The fire behaviour of reinforcement embedded in concrete is strongly conditioned both by its chemical composition and by the regulatory frameworks under which it is manufactured. This review considers carbon steels regulated by standards such as EN 10080 [61], UNE 36068:2011 [62], ASTM A615/615M [63], EN 10025-2 [64], ASTM A36/A36M [65], ASTM A706/706M [68], and UNE 36065:2011 [70], as well as stainless steels defined in standards such as UNE-EN 1992-1-2:2011 [11], EN 10088-1:2024 [85], and ASTM A955/A955M [86].

In the case of carbon steels, the carbon content ranges from 0.13% to 0.30%, a variation that directly affects the strength and ductility of the material. When the content exceeds 0.25%, as reported by Abbas et al. [79], the structure becomes more brittle upon exposure to heat, especially if cooling is rapid. Ruan et al. [73] documented a 60% increase in the corrosion rate after quenching in water from 850 °C, attributed to the formation of martensite. A similar effect was identified by Wang et al. [97], who directly link excess carbon to a significant loss of post-fire ductility. Manganese, present between 0.66% and 1.65%, provides hardness to steel by solid solution hardening. However, as Wang et al. [97] note, when it approaches 1.6%, it requires stabilisation with elements such as chromium or molybdenum to preserve its properties at high temperatures. Silicon, typically up to 0.80%, has a deoxidising function and improves oxidation resistance, and it is particularly useful in areas where the concrete has spalled and the reinforcement is exposed to fire [67,79].

As for structural steels such as S235JR or ASTM A36 [64,65], their low alloy level limits their thermal performance. However, the presence in small proportions of elements such as chromium (Cr), molybdenum (Mo), nickel (Ni), vanadium (V), boron (B), or titanium (Ti) can make a significant difference. For example, Mo (0.01–0.09%) and V (0.03%) contribute to delayed recrystallisation and improved creep resistance, as shown by studies such as those of Garrison et al. [98] who found clear improvements in structural capacity after exposure to high temperatures when these elements are present in appropriate proportions.

In the case of stainless steels, both austenitic, EN 1.4301, 1.4401, and duplex, 1.4362, 1.4462, alloys, all standardised according to EN 10088-1:2024 [85] and ASTM A955/A955M [86], were analysed. These steels are characterised by a high chromium content, between 16.75% and 24.5%, which allows them to form a stable passive layer, even after being exposed to fire. Albero et al. [81] demonstrated that EN 1.4301 retains more than 80% of its strength after heating to 700 °C and cooling in air, thanks to the joint action of chromium and nickel. The latter, present between 8.0% and 10.5%, stabilises the austenitic phase and helps to preserve ductility, even after demanding thermal cycles [84,87,92]. Duplex steels incorporate nitrogen, a key element that improves toughness and reduces intergranular segregation. Research such as Mehwish et al. [92] and Melo et al. [94] agree that EN 1.4462 maintains its cohesion and ductility even after a fire. In addition, molybdenum, which can be found up to 3.21%, enhances resistance to chloride corrosion and contributes to mechanical performance in high-temperature environments [81,82,83,84,87,88,89,90,91,92,93,94,95,96]. The present studies identify the Cr-Mo-Ni-N system as one of the most effective combinations for retaining structural properties after repeated thermal cycling. Overall, the data reviewed indicate that carbon steels, when properly formulated, can offer reasonable performance up to 600 °C; however, stainless steels, especially duplex steels, not only maintain their strength but also their ductility and chemical cohesion above 800 °C, positioning them as a safer and more reliable option for structures that could be directly exposed to fire.

3.2. Analysis of Mechanical Properties and Heating Applied or Fire-Exposed

Table 5 and Table 6 present the heating applied or fire-exposed and the mechanical properties analysed for carbon steels and stainless steels, respectively. These tables summarise the heating and cooling processes used in various studies, as well as the resulting mechanical properties, which are essential for determining the performance of these materials in various industrial and structural applications.

Table 5. Heating applied or fire-exposed and tests analysed in carbon steel.

Ref.	Heating Applied or Fire-Exposed	Mechanical Properties Analysed
[60]	- ISO 834 fire curve up to ~1000 °C - Duration up to 180 min - Natural air cooling	- Residual axial capacity - Axial/lateral deformations - Failure modes
[66]	- Heating 100–900 °C - 40 min soak - Natural air cooling	- Elastic modulus - Yield strength - Ultimate strength - Ductility - Fracture mode
[67]	- Slow heating to 800 °C - 45 min soak - Natural air cooling	- Yield strength - Ultimate strength - Elastic modulus - Strain at peak/failure - Microstructure
[69]	- ISO 834 to 650 °C - 60 min exposure - Natural cooling	- Ultimate strength - Axial load capacity - Section loss
[71]	- ISO 834 to >850 °C - Duration 30–180 min - Natural air cooling	- Axial/flexural residual strength - Thermal deformations - Buckling - Stress redistribution
[72]	- ASTM E119 fire curve - ~850 °C for 30 min - Natural air cooling	- Residual flexural moment - Bond loss - Structural damage (via UPV)
[73]	- Heating to 200, 500, 850 °C - 1 h soaking - Cooled in air or water	- Corrosion potential and rate - Mass loss - Microstructure (martensite, pearlite)
[74]	- Heating to 600 °C at 3 °C/s - 10 min soaking - No cooling studied	- Yield/ultimate strength - Ductility - Energy absorption - Thermal reduction factors
[75]	- Heating at 4–7 °C/min - 60 min soak at 400/800 °C - Natural air cooling	- Compressive/flexural strength - Porosity, sorptivity - Corrosion current and rate - Microstructure (SEM)
[76]	- Heated to 500/600/650 °C - 1 h soaking - Natural air cooling	- Microstructure only (martensite, ferrite, pearlite)
[77]	- Fire temps up to 1000 °C - 60–180 min ISO curve - Natural air cooling	- Residual load capacity (k-factor) - Displacements - Failure modes
[78]	- 25–1000 °C ramp in 100 °C steps - 60 min exposure	- Internal forces, displacements - Rotations, plastic hinge formation - Collapse time/temp
[79]	- Final rolling at 640 °C, 680 °C, 720 °C, 760 °C, and 800 °C	- Tensile strength - Yield strength - Elongation - Modulus of elasticity - Toughness modulus - Hardness
[80]	- Heating to 200 °C, 400 °C, 600 °C, 700 °C, 800 °C, and 1000 °C, followed by slow or rapid cooling	- Tensile strength - Ductility - Microhardness - Fracture behaviour
[81]	- Heating to 600 °C at 10 °C/min - Natural air cooling	- Bond strength - Slip displacement - Concrete compressive and tensile strength
[82]	- Heating to 900 °C - Soaking for 20 min - Cooling: Air or water	- Yield and ultimate strength - Strains (εy, εu), elongation (δ) - Ductility - Energy indices (P*, Id, A*, W)
[83]	- ISO-834 up to 800 °C - No cooling applied	- Elastic modulus - Yield/ultimate strength - Flexural strength - Connector slip
[84]	- Heating at 10 °C/min to 900 °C - 1h exposure - Cooling: Water, air, furnace	- Elastic modulus - Yield/ultimate strength - Ultimate strain (εu, εf) - Stress–strain curves

Table 5. Heating applied or fire-exposed and tests analysed in carbon steel.

Ref.	Heating Applied or Fire-Exposed	Mechanical Properties Analysed
[60]	- ISO 834 fire curve up to ~1000 °C - Duration up to 180 min - Natural air cooling	- Residual axial capacity - Axial/lateral deformations - Failure modes
[66]	- Heating 100–900 °C - 40 min soak - Natural air cooling	- Elastic modulus - Yield strength - Ultimate strength - Ductility - Fracture mode
[67]	- Slow heating to 800 °C - 45 min soak - Natural air cooling	- Yield strength - Ultimate strength - Elastic modulus - Strain at peak/failure - Microstructure
[69]	- ISO 834 to 650 °C - 60 min exposure - Natural cooling	- Ultimate strength - Axial load capacity - Section loss
[71]	- ISO 834 to >850 °C - Duration 30–180 min - Natural air cooling	- Axial/flexural residual strength - Thermal deformations - Buckling - Stress redistribution
[72]	- ASTM E119 fire curve - ~850 °C for 30 min - Natural air cooling	- Residual flexural moment - Bond loss - Structural damage (via UPV)
[73]	- Heating to 200, 500, 850 °C - 1 h soaking - Cooled in air or water	- Corrosion potential and rate - Mass loss - Microstructure (martensite, pearlite)
[74]	- Heating to 600 °C at 3 °C/s - 10 min soaking - No cooling studied	- Yield/ultimate strength - Ductility - Energy absorption - Thermal reduction factors
[75]	- Heating at 4–7 °C/min - 60 min soak at 400/800 °C - Natural air cooling	- Compressive/flexural strength - Porosity, sorptivity - Corrosion current and rate - Microstructure (SEM)
[76]	- Heated to 500/600/650 °C - 1 h soaking - Natural air cooling	- Microstructure only (martensite, ferrite, pearlite)
[77]	- Fire temps up to 1000 °C - 60–180 min ISO curve - Natural air cooling	- Residual load capacity (k-factor) - Displacements - Failure modes
[78]	- 25–1000 °C ramp in 100 °C steps - 60 min exposure	- Internal forces, displacements - Rotations, plastic hinge formation - Collapse time/temp
[79]	- Final rolling at 640 °C, 680 °C, 720 °C, 760 °C, and 800 °C	- Tensile strength - Yield strength - Elongation - Modulus of elasticity - Toughness modulus - Hardness
[80]	- Heating to 200 °C, 400 °C, 600 °C, 700 °C, 800 °C, and 1000 °C, followed by slow or rapid cooling	- Tensile strength - Ductility - Microhardness - Fracture behaviour
[81]	- Heating to 600 °C at 10 °C/min - Natural air cooling	- Bond strength - Slip displacement - Concrete compressive and tensile strength
[82]	- Heating to 900 °C - Soaking for 20 min - Cooling: Air or water	- Yield and ultimate strength - Strains (εy, εu), elongation (δ) - Ductility - Energy indices (P*, Id, A*, W)
[83]	- ISO-834 up to 800 °C - No cooling applied	- Elastic modulus - Yield/ultimate strength - Flexural strength - Connector slip
[84]	- Heating at 10 °C/min to 900 °C - 1h exposure - Cooling: Water, air, furnace	- Elastic modulus - Yield/ultimate strength - Ultimate strain (εu, εf) - Stress–strain curves

Table 6. Heating applied or fire-exposed and tests analysed in stainless steel.

Ref.	Heating Applied or Fire-Exposed	Mechanical Properties Analysed
[81]	- Heating to 600 °C at 10 °C/min - Natural air cooling	- Bond strength - Slip displacement - Concrete compressive and tensile strength
[82]	- Heating to 900 °C - Soaking for 20 min - Cooling: air or water	- Yield and ultimate strength - Strains (εy, εu), elongation (δ) - Ductility - Energy indices (P*, Id, A*, W)
[83]	- ISO-834 up to 800 °C - No cooling applied	- Elastic modulus - Yield/ultimate strength - Flexural strength - Connector slip
[84]	- Heating at 10 °C/min to 900 °C - 1h exposure - Cooling: Water, air, furnace	- Elastic modulus - Yield/ultimate strength - Ultimate strain (εu, εf) - Stress–strain curves
[87]	- Heating up to 838 °C - Soaking for 20 min - Cooling: Furnace (slow) or water (fast)	- Elastic modulus (E) - Yield strength (f0.2) - Ultimate strength (fu) - Ultimate strain (εu) - Fracture resistance
[88]	- Simulated uniform temps: 350 °C, 600 °C, 700 °C	- Yield strength (0.2%, 2%) - Ultimate strength - Elastic modulus - Axial-bending interaction (N-M) - Collapse modes
[89]	- Heating up to 1200 °C - Various cooling methods: Air, furnace, water	- Yield strength (fy) - Elastic modulus (E) - Ultimate tensile strength (fu) - Ultimate strain (εu)
[90]	- Heating to 1000 °C at 2.78 °C/s - 10 min soaking - No cooling post-test	- Yield and ultimate strength - Strain (εu, εf) - Area reduction (Z) - Hardness, energy, stress–strain
[91]	- Ramp: 20 °C/min then 10 min soak - Exposure: 30/180 min - Cooling: Air or water (200 mL)	- Elastic modulus - Yield strength - Ultimate tensile strength - Fracture stress - Ductility
[92]	- ASTM E119 up to 850 °C - Natural air cooling	- Flexural capacity - Deflection - Failure modes
[93]	- Isothermal and transitory heating up to 1000 °C. No water cooling (natural cooling only)	- Elastic modulus E - Yield/ultimate strength fy (0.2%), fu - Ultimate strain εu, εf - Stress–strain curves
[94]	- Heating to high temperatures not specified	- Tensile strength - Slip behaviour of the joint - Load–displacement response - Energy dissipation
[95]	- Standard fire exposure for 30 and 90 min, followed by natural cooling. Temperatures ranged from 20 to 1000 °C.	- Tensile strength - Energy dissipation capacity - Ductility - Secant stiffness
[96]	- Heating at 400 °C, 600 °C, 800 °C, and 1000 °C, followed by air cooling.	- Cold compression strength (CCS) - Pull-out deformation energy - Tensile strength of steel bars

Table 6. Heating applied or fire-exposed and tests analysed in stainless steel.

Ref.	Heating Applied or Fire-Exposed	Mechanical Properties Analysed
[81]	- Heating to 600 °C at 10 °C/min - Natural air cooling	- Bond strength - Slip displacement - Concrete compressive and tensile strength
[82]	- Heating to 900 °C - Soaking for 20 min - Cooling: air or water	- Yield and ultimate strength - Strains (εy, εu), elongation (δ) - Ductility - Energy indices (P*, Id, A*, W)
[83]	- ISO-834 up to 800 °C - No cooling applied	- Elastic modulus - Yield/ultimate strength - Flexural strength - Connector slip
[84]	- Heating at 10 °C/min to 900 °C - 1h exposure - Cooling: Water, air, furnace	- Elastic modulus - Yield/ultimate strength - Ultimate strain (εu, εf) - Stress–strain curves
[87]	- Heating up to 838 °C - Soaking for 20 min - Cooling: Furnace (slow) or water (fast)	- Elastic modulus (E) - Yield strength (f0.2) - Ultimate strength (fu) - Ultimate strain (εu) - Fracture resistance
[88]	- Simulated uniform temps: 350 °C, 600 °C, 700 °C	- Yield strength (0.2%, 2%) - Ultimate strength - Elastic modulus - Axial-bending interaction (N-M) - Collapse modes
[89]	- Heating up to 1200 °C - Various cooling methods: Air, furnace, water	- Yield strength (fy) - Elastic modulus (E) - Ultimate tensile strength (fu) - Ultimate strain (εu)
[90]	- Heating to 1000 °C at 2.78 °C/s - 10 min soaking - No cooling post-test	- Yield and ultimate strength - Strain (εu, εf) - Area reduction (Z) - Hardness, energy, stress–strain
[91]	- Ramp: 20 °C/min then 10 min soak - Exposure: 30/180 min - Cooling: Air or water (200 mL)	- Elastic modulus - Yield strength - Ultimate tensile strength - Fracture stress - Ductility
[92]	- ASTM E119 up to 850 °C - Natural air cooling	- Flexural capacity - Deflection - Failure modes
[93]	- Isothermal and transitory heating up to 1000 °C. No water cooling (natural cooling only)	- Elastic modulus E - Yield/ultimate strength fy (0.2%), fu - Ultimate strain εu, εf - Stress–strain curves
[94]	- Heating to high temperatures not specified	- Tensile strength - Slip behaviour of the joint - Load–displacement response - Energy dissipation
[95]	- Standard fire exposure for 30 and 90 min, followed by natural cooling. Temperatures ranged from 20 to 1000 °C.	- Tensile strength - Energy dissipation capacity - Ductility - Secant stiffness
[96]	- Heating at 400 °C, 600 °C, 800 °C, and 1000 °C, followed by air cooling.	- Cold compression strength (CCS) - Pull-out deformation energy - Tensile strength of steel bars

In carbon steels, testing conditions replicate temperatures of up to 850–1000 °C, for durations ranging from 30 to 180 min, with natural cooling in most cases [60,65,71,72,77]. At these temperatures, a significant loss of mechanical properties is observed, particularly in terms of yield strength and load-bearing capacity under axial or flexural loads. Studies such as [60,71,72] show that B500A and B500C reinforcement bars, commonly used in columns and beams, can lose between 40% and 85% of their structural strength after moderate-intensity fires, especially when high-strength concrete is used.

Other research, including the studies of [66,67,74,79], focuses on tensile tests and mechanical characterisation following controlled heating up to 800–900 °C. The findings indicate that the loss of structural stiffness, reflected in the reduction in the modulus of elasticity precedes the drop in strength. Ductility remains relatively stable up to 400–500 °C but begins to deteriorate rapidly beyond 600 °C, particularly in plain carbon steels without alloying elements. Studies like [75,78] highlight how the accumulation of plastic deformations and the formation of plastic hinges become more pronounced as the steel internal structure degrades under prolonged thermal exposure.

In contrast, stainless steels show a more favourable thermal response. Various studies [81,82,83,84,87,88,89,90,91,92] report greater stability in properties like yield strength, ductility, and modulus of elasticity, even after exposure to temperatures above 800 °C. EN 1.4301 has demonstrated the ability to retain 70–80% of its strength after exposure to 600–700 °C, as well as good deformation recovery [82,87,91]. Post-fire cold tensile tests also show that this type of steel dissipates more energy and exhibits greater fracture toughness compared to carbon steels under similar conditions [84,90]. One of the most relevant factors in these studies is the cooling method. Natural cooling, used predominantly in studies [79,83,92], helps preserve ductility and delays the onset of brittle failures. In contrast, rapid water cooling, used in studies [82,84,91], can induce internal stresses that negatively affect deformation capacity, especially if not properly controlled.

From a structural perspective, stainless steels also show less bond degradation with concrete after fire exposure. This is attributed to their lower thermal expansion coefficient and greater resistance to surface corrosion. Research such as [81,92] confirms that, even at temperatures up to 600 °C, stainless steel bars maintain their anchorage capacity better than carbon steel reinforcement.

Recent studies have reported comparable effects, underlining the stabilising role of chromium, nickel, and molybdenum in steel microstructures exposed to repeated thermal cycles, although these analyses did not specifically focus on embedded reinforcement [99]. Additional research has also addressed aspects related to thermal performance in advanced alloys and steel variants, providing valuable information on damage mechanisms and high-temperature behaviour [100,101,102].

3.3. Main Results and Conclusions on Carbon Steel and Stainless Steel

This final section presents the main results and conclusions drawn from the analysis of the studies summarised in Table 7 and Table 8, which correspond to carbon steel and stainless steel. The analysis provides a comprehensive understanding of how hardness, tensile strength, ductility, and other key properties are optimised through specific processing conditions.

Table 7. Main results and conclusions for carbon steel.

Ref.	Main Results	Conclusions
[60]	- Fire resistance decreases with axial load/slenderness - Larger sections improve performance - Simplified equations proposed	- TRC columns outperform conventional ones under fire - Design formulas proposed
[66]	- Stable ≤ 200 °C - Yield strength drops to 15% at 700 °C - CTR bars more ductile when hot	- HRD/TMT degrade progressively - CTR retains ductility - Findings match international standards
[67]	- Degradation starts at 400–700 °C - Ultimate strength ~40% at 600 °C - Elastic modulus degrades faster	- ASTM A706 performs best - Eurocode is conservative - Improved model proposed
[69]	- A total of 60% loss in strength with 20% corrosion + fire - Epoxy coating reduces damage	- Fire + corrosion severely weaken bars - Epoxy coating is protective - Fire-damaged RC must be reassessed
[71]	- Initial high fire resistance - Spalling prevented by PP fibres - Strength loss after 90 min exposure	- High-strength composite columns resist fire well initially - Design method with tables proposed
[72]	- Residual strength drops up to 85% in high-strength concrete beams - Internal pressure causes spalling - Crack scoring correlates with mass loss	- Corrosion + fire cause major structural degradation - High-strength concretes are more vulnerable - Codes should consider these combined effects
[73]	- Fire exposure increases corrosion risk - Water quenching at 850 °C was most damaging (+60% corrosion rate)	- Thermal exposure lowers corrosion resistance - Water cooling forms martensite, higher corrosion susceptibility
[74]	- Strength increases with strain rate - Properties degrade with temp - Strain ageing at 200–300 °C	- B500A shows resistance in extreme conditions - Model Code 2010 conservative under dynamic fire/explosion - Calibrated models proposed
[75]	- CNT mortars retained +10% fc and +32% fr at 800 °C - A total of 3–6% lower porosity/sorptivity - A 58% lower corrosion rate	- MWCNTs improve fire and corrosion resistance - Act as crack bridges and reduce porosity - Better steel–mortar interface cohesion
[76]	- Martensite transforms to ferrite/pearlite with heat - Fully recrystallised grains at 650 °C	- Lack of martensite stabilisers = loss of thermal strength - TMT bars become structurally weak after fire
[77]	- Strength loss grows with fire temp/duration - Concrete strength most influential (up to 32.9%)	- SRC columns retain substantial post-fire capacity - Analytical expression proposed for residual strength
[78]	- RC building did not collapse even at 1000 °C - Steel structure failed at 807 °C (31.6 min)	- Concrete cover key to RC fire resistance - Steel frames collapse rapidly if unprotected
[79]	- Higher final rolling temperatures increased grain size, decreasing tensile strength, yield strength, and hardness but increased elongation and toughness modulus - Higher carbon content increased hardness, tensile strength, and yield strength but decreased elongation and toughness modulus. - The steel bars met ASTM A615 standards for strength and weight per unit length	- The final rolling temperature and carbon content have a significant impact on the mechanical properties of steel reinforcement bars - The production of reinforcement bars from local scrap can meet ASTM standards if processing variables are properly controlled - Measures should be implemented to better control the chemical composition and final rolling temperatures in the local industry to improve the quality of reinforcement steel
[80]	- Steel bars previously exposed to fire conditions showed high sensitivity to cooling intensity. - Specimens heated and quenched in water showed an increase in tensile strength but a significant decrease in material plasticity.	- The ductile-to-brittle transition is influenced by the segregation of nitrogen atoms and localised internal stresses at austenite grain boundaries - The anisotropy of residual stresses affects the localization of elastic deformations and brittle cleavage fracture
[81]	- Bond loss proportional to concrete strength loss - Stainless and galvanised bars performed best - Predictive model proposed	- Thermal bond degradation manageable with corrosion-resistant bars - Design model modification proposed
[82]	- Strength stable <600 °C, drops above 700 °C - Water cooling reduces ductility more - Models validated	- SCBSBs retain cladding integrity post-fire - Water cooling more damaging - Constitutive models proposed
[83]	- Strength drops above 600 °C - Slip crucial in design - Traditional methods underestimate deformation	- Design should include connector slip and SS-specific behaviour - Proposed method improves fire resistance prediction
[84]	- Strength retained to 600 °C, drops >700 °C - Water cooling increases ductility - SS more stable than carbon	- EN 1.4301 performs well post-fire - Suitable for reuse - Cooling method mainly affects ductility

Table 7. Main results and conclusions for carbon steel.

Ref.	Main Results	Conclusions
[60]	- Fire resistance decreases with axial load/slenderness - Larger sections improve performance - Simplified equations proposed	- TRC columns outperform conventional ones under fire - Design formulas proposed
[66]	- Stable ≤ 200 °C - Yield strength drops to 15% at 700 °C - CTR bars more ductile when hot	- HRD/TMT degrade progressively - CTR retains ductility - Findings match international standards
[67]	- Degradation starts at 400–700 °C - Ultimate strength ~40% at 600 °C - Elastic modulus degrades faster	- ASTM A706 performs best - Eurocode is conservative - Improved model proposed
[69]	- A total of 60% loss in strength with 20% corrosion + fire - Epoxy coating reduces damage	- Fire + corrosion severely weaken bars - Epoxy coating is protective - Fire-damaged RC must be reassessed
[71]	- Initial high fire resistance - Spalling prevented by PP fibres - Strength loss after 90 min exposure	- High-strength composite columns resist fire well initially - Design method with tables proposed
[72]	- Residual strength drops up to 85% in high-strength concrete beams - Internal pressure causes spalling - Crack scoring correlates with mass loss	- Corrosion + fire cause major structural degradation - High-strength concretes are more vulnerable - Codes should consider these combined effects
[73]	- Fire exposure increases corrosion risk - Water quenching at 850 °C was most damaging (+60% corrosion rate)	- Thermal exposure lowers corrosion resistance - Water cooling forms martensite, higher corrosion susceptibility
[74]	- Strength increases with strain rate - Properties degrade with temp - Strain ageing at 200–300 °C	- B500A shows resistance in extreme conditions - Model Code 2010 conservative under dynamic fire/explosion - Calibrated models proposed
[75]	- CNT mortars retained +10% fc and +32% fr at 800 °C - A total of 3–6% lower porosity/sorptivity - A 58% lower corrosion rate	- MWCNTs improve fire and corrosion resistance - Act as crack bridges and reduce porosity - Better steel–mortar interface cohesion
[76]	- Martensite transforms to ferrite/pearlite with heat - Fully recrystallised grains at 650 °C	- Lack of martensite stabilisers = loss of thermal strength - TMT bars become structurally weak after fire
[77]	- Strength loss grows with fire temp/duration - Concrete strength most influential (up to 32.9%)	- SRC columns retain substantial post-fire capacity - Analytical expression proposed for residual strength
[78]	- RC building did not collapse even at 1000 °C - Steel structure failed at 807 °C (31.6 min)	- Concrete cover key to RC fire resistance - Steel frames collapse rapidly if unprotected
[79]	- Higher final rolling temperatures increased grain size, decreasing tensile strength, yield strength, and hardness but increased elongation and toughness modulus - Higher carbon content increased hardness, tensile strength, and yield strength but decreased elongation and toughness modulus. - The steel bars met ASTM A615 standards for strength and weight per unit length	- The final rolling temperature and carbon content have a significant impact on the mechanical properties of steel reinforcement bars - The production of reinforcement bars from local scrap can meet ASTM standards if processing variables are properly controlled - Measures should be implemented to better control the chemical composition and final rolling temperatures in the local industry to improve the quality of reinforcement steel
[80]	- Steel bars previously exposed to fire conditions showed high sensitivity to cooling intensity. - Specimens heated and quenched in water showed an increase in tensile strength but a significant decrease in material plasticity.	- The ductile-to-brittle transition is influenced by the segregation of nitrogen atoms and localised internal stresses at austenite grain boundaries - The anisotropy of residual stresses affects the localization of elastic deformations and brittle cleavage fracture
[81]	- Bond loss proportional to concrete strength loss - Stainless and galvanised bars performed best - Predictive model proposed	- Thermal bond degradation manageable with corrosion-resistant bars - Design model modification proposed
[82]	- Strength stable <600 °C, drops above 700 °C - Water cooling reduces ductility more - Models validated	- SCBSBs retain cladding integrity post-fire - Water cooling more damaging - Constitutive models proposed
[83]	- Strength drops above 600 °C - Slip crucial in design - Traditional methods underestimate deformation	- Design should include connector slip and SS-specific behaviour - Proposed method improves fire resistance prediction
[84]	- Strength retained to 600 °C, drops >700 °C - Water cooling increases ductility - SS more stable than carbon	- EN 1.4301 performs well post-fire - Suitable for reuse - Cooling method mainly affects ductility

Table 8. Main results and conclusions for stainless steel.

Ref.	Main Results	Conclusions
[81]	- Bond loss proportional to concrete strength loss - Stainless and galvanised bars performed best - Predictive model proposed	- Thermal bond degradation manageable with corrosion-resistant bars - Design model modification proposed
[82]	- Strength stable <600 °C, drops above 700 °C - Water cooling reduces ductility more - Models validated	- SCBSBs retain cladding integrity post-fire - Water cooling more damaging - Constitutive models proposed
[83]	- Strength drops above 600 °C - Slip crucial in design - Traditional methods underestimate deformation	- Design should include connector slip and SS-specific behaviour - Proposed method improves fire resistance prediction
[84]	- Strength retained to 600 °C, drops >700 °C - Water cooling increases ductility - SS more stable than carbon	- EN 1.4301 performs well post-fire - Suitable for reuse - Cooling method mainly affects ductility
[87]	- Stainless steels retain more strength than carbon - Fast cooling improves strength but reduces ductility - Retention factors proposed per steel type and temperature	- Stainless steels often reusable after fire - Safety factors should depend on fire history - Load history crucial for assessment
[88]	- EC3 is conservative for EHS - Kucukler’s method more accurate and economical - Slenderness, material, and moment diagram key parameters	- EC3 unsuitable for EHS stainless columns - New methods needed based on slenderness and steel grade
[89]	- Retention factors (Rh) defined per steel and temperature - Austenitic steels retained better properties - Ferritic steels degraded faster - Safety factors proposed based on reliability index β	- Applicable to carbon and stainless steels - Reuse more feasible with stainless - Reliability-based safety factors recommended
[90]	- Strength decreases with temp, rises with strain rate - Ductility increases at high temp - Dynamic factors proposed	- 1.4301 shows good ductility under extreme fire + blast - Predictive models suitable for design
[91]	- Properties stable to 1000 °C - Yield drops after 700 °C - Cooling method has minor effect	- Residual properties remain usable post-fire - Predictive equations developed for residual strength
[92]	- SSRC beams outperformed carbon steel beams - Higher deformation capacity and fire duration	- SSRC beams highly fire-resistant - Fire design should consider SS-specific data
[93]	Stainless steels retain higher strength and stiffness than carbon steels above 550 °C. Reduction factors proposed by steel grade.	Suitable for fire-resistant design up to 500 MPa class. Ramberg–Osgood model fits well. Limited by lack of cooling data.
[94]	1. Duplex stainless steel bars EN 1.4462 show better ductility and work hardening compared to carbon steel. 2. Columns reinforced with stainless steel exhibit better load capacity and ductility under cyclic loads.	1. The use of duplex stainless steel EN 1.4462 improves the cyclic behaviour of reinforced concrete columns compared to the use of carbon steel. 2. Stainless steel bars exhibit greater bond slip and enhance the energy dissipation capacity under cyclic loading conditions.
[95]	1. A 30 min fire exposure resulted in moderate damage, while a 90 min exposure caused extensive cracking and disintegration of the concrete layer. 2. Strengthened columns after fire exposure showed better lateral load capacity and ductility compared to columns not exposed to fire.	1. Fire exposure significantly affects the stiffness and load-bearing capacity of reinforced concrete columns. 2. Strengthening techniques using CFRP (carbon fibre-reinforced polymer) significantly improve the cyclic behaviour and energy dissipation capacity of fire-damaged columns.
[96]	1. LCC samples treated at 1000 °C showed a significant increase in compression strength. 2. The pull-out deformation energy does not directly correlate with cold compression strength. 3. The mineral composition significantly impacts the joint strength.	1. The 304 stainless steel bars form a reliable bond with the refractory materials analysed. 2. There is no direct correlation between compressive strength and pull-out deformation energy. 3. Mineral transformations, such as the formation of mullite and corundum, significantly affect the bond strength.

Table 8. Main results and conclusions for stainless steel.

Ref.	Main Results	Conclusions
[81]	- Bond loss proportional to concrete strength loss - Stainless and galvanised bars performed best - Predictive model proposed	- Thermal bond degradation manageable with corrosion-resistant bars - Design model modification proposed
[82]	- Strength stable <600 °C, drops above 700 °C - Water cooling reduces ductility more - Models validated	- SCBSBs retain cladding integrity post-fire - Water cooling more damaging - Constitutive models proposed
[83]	- Strength drops above 600 °C - Slip crucial in design - Traditional methods underestimate deformation	- Design should include connector slip and SS-specific behaviour - Proposed method improves fire resistance prediction
[84]	- Strength retained to 600 °C, drops >700 °C - Water cooling increases ductility - SS more stable than carbon	- EN 1.4301 performs well post-fire - Suitable for reuse - Cooling method mainly affects ductility
[87]	- Stainless steels retain more strength than carbon - Fast cooling improves strength but reduces ductility - Retention factors proposed per steel type and temperature	- Stainless steels often reusable after fire - Safety factors should depend on fire history - Load history crucial for assessment
[88]	- EC3 is conservative for EHS - Kucukler’s method more accurate and economical - Slenderness, material, and moment diagram key parameters	- EC3 unsuitable for EHS stainless columns - New methods needed based on slenderness and steel grade
[89]	- Retention factors (Rh) defined per steel and temperature - Austenitic steels retained better properties - Ferritic steels degraded faster - Safety factors proposed based on reliability index β	- Applicable to carbon and stainless steels - Reuse more feasible with stainless - Reliability-based safety factors recommended
[90]	- Strength decreases with temp, rises with strain rate - Ductility increases at high temp - Dynamic factors proposed	- 1.4301 shows good ductility under extreme fire + blast - Predictive models suitable for design
[91]	- Properties stable to 1000 °C - Yield drops after 700 °C - Cooling method has minor effect	- Residual properties remain usable post-fire - Predictive equations developed for residual strength
[92]	- SSRC beams outperformed carbon steel beams - Higher deformation capacity and fire duration	- SSRC beams highly fire-resistant - Fire design should consider SS-specific data
[93]	Stainless steels retain higher strength and stiffness than carbon steels above 550 °C. Reduction factors proposed by steel grade.	Suitable for fire-resistant design up to 500 MPa class. Ramberg–Osgood model fits well. Limited by lack of cooling data.
[94]	1. Duplex stainless steel bars EN 1.4462 show better ductility and work hardening compared to carbon steel. 2. Columns reinforced with stainless steel exhibit better load capacity and ductility under cyclic loads.	1. The use of duplex stainless steel EN 1.4462 improves the cyclic behaviour of reinforced concrete columns compared to the use of carbon steel. 2. Stainless steel bars exhibit greater bond slip and enhance the energy dissipation capacity under cyclic loading conditions.
[95]	1. A 30 min fire exposure resulted in moderate damage, while a 90 min exposure caused extensive cracking and disintegration of the concrete layer. 2. Strengthened columns after fire exposure showed better lateral load capacity and ductility compared to columns not exposed to fire.	1. Fire exposure significantly affects the stiffness and load-bearing capacity of reinforced concrete columns. 2. Strengthening techniques using CFRP (carbon fibre-reinforced polymer) significantly improve the cyclic behaviour and energy dissipation capacity of fire-damaged columns.
[96]	1. LCC samples treated at 1000 °C showed a significant increase in compression strength. 2. The pull-out deformation energy does not directly correlate with cold compression strength. 3. The mineral composition significantly impacts the joint strength.	1. The 304 stainless steel bars form a reliable bond with the refractory materials analysed. 2. There is no direct correlation between compressive strength and pull-out deformation energy. 3. Mineral transformations, such as the formation of mullite and corundum, significantly affect the bond strength.

The analysis of the selected studies reveals a clear distinction in the mechanical behaviour of carbon steels versus stainless steels when both are subjected to high temperatures. In the case of carbon steel, the results show a progressive loss of load-bearing capacity starting at 400–500 °C, with much more pronounced degradation beyond 600 °C. This decline affects not only the modulus of elasticity but also tensile strength, ductility, and, in certain cases, bond strength with concrete. The situation worsens when the reinforcement is already corroded, combining chemical damage with thermal degradation, as pointed out in studies such as [69,72,75]. This dual effect compromises structural strength and induces microstructural changes that promote the formation of more brittle phases after heating.

Several works have also explored the impact of post-heating cooling methods. Rapid cooling with water has been shown to trigger the formation of martensite in areas where the critical temperature threshold, typically above 850 °C, has been reached or exceeded. This phenomenon, documented in studies like [73,76], negatively affects the steel ability to recover its mechanical properties, resulting in a more brittle response. Martensitic transformation is observed more frequently in exposed reinforcement or bars with damaged coatings, which mirrors real-life scenarios where concrete has lost its insulating function due to cracks or spalling [78].

In contrast, austenitic stainless steels exhibit a much more stable thermal response. Research such as [82,83,87,89] shows that these materials can retain 70–80% of their yield strength even after exposure to temperatures exceeding 700 °C. This mechanical stability is not significantly affected by the cooling method, indicating an intrinsic thermal resistance linked to their microstructure and to the presence of alloying elements such as chromium, nickel, and molybdenum. Additionally, critical properties such as ductility and energy dissipation capacity remain high, which is crucial for structures that must continue bearing loads after a severe thermal event.

Taken together, these findings reinforce the idea that, while carbon steel may perform adequately under moderate and controlled thermal conditions, its behaviour is severely compromised in scenarios involving a loss of cover, corrosion, or rapid cooling. In contrast, stainless steels, particularly EN 1.4301, demonstrate a much more robust response profile, showing lower sensitivity to thermal and mechanical degradation even under extreme conditions. This contrast highlights the importance of selecting the appropriate type of steel based on the fire exposure risk and the condition of the concrete, especially in existing structures or environments where durability against aggressive agents is a critical concern.

4. Discussion

The results of this systematic review show that the thermal and mechanical behaviour of reinforcing steel exposed to high temperatures cannot be analysed in isolation. There is a clear interaction between the chemical composition of the steel, the thermal conditions to which it has been subjected, and the type of subsequent cooling, especially in structures where the concrete was previously damaged or corroded, leaving the reinforcement unprotected.

In the case of carbon steel, numerous studies have shown that significant losses in mechanical properties, such as strength, ductility, and bearing capacity, begin to manifest themselves at 500 °C [60,69,72,75]. This degradation is aggravated when the reinforcement has undergone corrosion processes or is exposed by the deterioration of the concrete coating, which favours the formation of brittle phases such as martensite, particularly under rapid cooling conditions [79,80]. A study conducted by Kültür, Ö. F. et al. [78] confirms that, in corroded structures, the surface temperature of reinforcing bars can exceed 800 °C, and, under these conditions, the concrete loses its insulating capacity. Abrupt cooling causes localised martensitic transformations, in agreement with the results observed in experimental studies.

In contrast, stainless steels, especially austenitic and duplex stainless steels, exhibit considerably more stable thermal behaviour. Research such as that reported in [81,82,83,84,87,91,92] indicates that these materials can retain 70–80% of their yield strength even after prolonged exposure to temperatures more than 700 °C. This ability is attributed to their microstructure and to the presence of elements such as the austenitic and duplex types. This retention capability is attributed to their microstructure and the presence of elements such as chromium, nickel, and molybdenum, which help prevent the formation of brittle phases such as sigma or chi, provided that thermal cycling is properly controlled [82,87,93]. In addition, properties such as ductility and energy dissipation are maintained at high levels, making stainless steels a more reliable option for structures that must retain their integrity after a fire.

However, the literature reviewed shows a remarkable variability in the experimental protocols used, which makes direct comparison between studies difficult. Differences in heating rates, exposure times, cooling methods, and specimen geometry limit the extrapolation of results. In addition, many tests are performed under small-scale laboratory conditions, which do not accurately reflect the actual behaviour of embedded reinforcement in concrete structural elements [84,90,94]. Even so, some clear trends emerge: carbon steel shows a higher vulnerability to fire, especially where corrosion or the loss of coating is present, while stainless steels, particularly EN 1.4301, offer a more robust and consistent performance. A higher proportion of nickel and molybdenum in the chemical composition has been shown to be associated with better retention of mechanical properties after thermal exposure [87,92]. These findings reinforce the need for structural fire-resistant design to transcend the requirements set by standard codes for each steel type, considering instead the specific chemical.

This approach becomes particularly relevant when considering that real fires do not follow ideal conditions but are usually high-intensity, short-duration events, developed in environments where dynamic loads and chemically aggressive agents may coexist [99,102,103]. In such circumstances, the bond between steel and concrete can be considerably reduced—or even completely lost—due to thermal degradation and the loss of surface roughness.

In this context, the present systematic review recommends several priority actions to strengthen the scientific basis for fire-resistant structural design:

• Standardise post-fire thermal characterisation procedures, including parameters such as heating rate, hold time, and testing atmospheres.
• Scale up testing, incorporating full-size specimens and extended thermal cycles to more realistically simulate real-world service conditions in buildings.
• Incorporate advanced technologies, such as 3D volumetric scanning, to detect microstructural changes, mass loss, or surface defects after fire exposure.
• Promote an interdisciplinary approach that brings together metallurgy, material science, structural engineering, and sustainability to develop safer, more durable, and cost-effective steels.
• Improve mathematical modelling by applying statistical tools to identify patterns affecting each test condition, thereby enabling more accurate and reliable formulation of predictive equations.
• Conduct cost analysis studies to explore strategies for reducing the production and application costs of stainless steel, thus enhancing its feasibility and adoption in building construction.

Addressing these action points will contribute to the development of passive reinforcement systems with increased fire resistance, in line with modern building requirements and capable of dealing with infrequent but high impact fires. In doing so, it lays the foundation for future structural codes that incorporate more precise thermal design criteria backed by sound science.

5. Conclusions

This systematic review identified relevant patterns in the thermal and mechanical behaviour of carbon and stainless steel reinforcement subjected to high temperatures and subsequent cooling processes, in the specific context of reinforced concrete structures exposed to fire.

• Carbon steel reinforcement shows a significant degradation of its mechanical properties when exposed to temperatures above 500 °C. Their behaviour after cooling is highly dependent on the chemical composition (carbon content, manganese, silicon, etc.) and the type of cooling (fast or slow), in some cases showing brittle microstructures.
• Stainless steels, especially austenitic and duplex steels, have shown higher thermal stability and higher residual strength and ductility after being subjected to high temperatures. Elements such as chromium, nickel, and molybdenum play a decisive role in this behaviour compared to carbon steel. However, exposure to extreme thermal conditions or uncontrolled cooling cycles, either during or after a fire, can favour the formation of brittle intermetallic phases in stainless steels, which compromises their structural stability.
• Considerable methodological heterogeneity is observed among the studies analysed, both in thermal exposures and in test scales and cooling conditions. This lack of homogeneity makes it difficult to extrapolate the results directly to professional practice and underlines the need to standardise mechanical testing procedures after a fire or at high temperatures.

Finally, there is an urgent need for experimental studies on a real scale, with thermal parameters representative of building fires, which will allow a more realistic evaluation of the behaviour of reinforcement embedded in concrete when subjected to high temperatures. Based on these results, it will be possible to design new types of steel with better thermal resilience that are safer, more sustainable, and adjusted to the current needs of the building sector.