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24 pages, 14767 KB

Open AccessArticle

The Effect of Mo Content on the Multi-Scale Martensitic Structure and Mechanical Properties of Ultra-High-Strength and -Toughness Oil Well Pipes

by Bin Shi, Shibiao Wang, Chunling Zhang and Qingfeng Wang

Metals 2026, 16(4), 365; https://doi.org/10.3390/met16040365 - 26 Mar 2026

Viewed by 373

Abstract

The study systematically investigates the effect of molybdenum (Mo) content (0.70–1.57 wt.%) on the microstructure and mechanical properties of quenched and tempered martensitic steel for ultra-high-strength and -toughness oil well pipes. The results demonstrate that increasing the Mo content substantially enhances the strength [...] Read more.

The study systematically investigates the effect of molybdenum (Mo) content (0.70–1.57 wt.%) on the microstructure and mechanical properties of quenched and tempered martensitic steel for ultra-high-strength and -toughness oil well pipes. The results demonstrate that increasing the Mo content substantially enhances the strength of the steel. The yield strength (YS) increases from 1135 MPa to 1233 MPa, the ultimate tensile strength (UTS) rises from 1176 MPa to 1285 MPa, and the elongation after fracture is marginally improved to 19%. However, the low-temperature impact energy (AKV₂) of the steel at −20 °C exhibits a pronounced decrease, from 117 J to 36 J. Mo refines the multi-scale martensitic microstructure, increases the fraction of high-angle grain boundaries (HAGBs) and dislocation density, and promotes the precipitation of three types of carbides. Quantitative analysis indicates that grain refinement strengthening is the predominant factor contributing to the enhancement of steel strength. The decline in the steel’s resistance to low temperatures is attributed to the separation of coarse, blocky M₃C-type carbides at the grain boundaries. This results in the accumulation of stress at these boundaries, leading to a transformation in the steel’s fracture mode from ductile to brittle. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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16 pages, 9419 KB

Open AccessArticle

Nitrogen Content Effects on Microstructural Evolution and Low-Temperature Impact Toughness in the Coarse-Grained Heat-Affected Zone of Welded X70 Pipeline Steel

by Jiangcheng Liu, Kai Guo, Haote Ma, Jiangli He, Junchao Wang, Chuanyou Zhang, Tiansheng Wang and Qingfeng Wang

Metals 2026, 16(3), 331; https://doi.org/10.3390/met16030331 - 16 Mar 2026

Viewed by 389

Abstract

The low-temperature toughness of a coarse-grained heat-affected zone (CGHAZ) is a critical factor governing the service safety of welded joints in X70 pipeline steel. This study systematically investigated the influence of nitrogen content (ranging from 0.0018 to 0.0120 wt%) on the microstructure and [...] Read more.

The low-temperature toughness of a coarse-grained heat-affected zone (CGHAZ) is a critical factor governing the service safety of welded joints in X70 pipeline steel. This study systematically investigated the influence of nitrogen content (ranging from 0.0018 to 0.0120 wt%) on the microstructure and low-temperature impact toughness of the CGHAZ in X70 pipeline steel using welding thermal simulation tests with a heat input of 12.5 kJ/cm. The results indicate that the CGHAZ microstructure predominantly comprises lath bainite (LB) and minor martensite–austenite (M/A) constituents. With increasing nitrogen content, the austenite-to-ferrite transformation start temperature (Ar₃) increased while the transformation finish temperature (Ar₁) decreased, resulting in coarsening of the lath bainite packet structure. The M/A volume fraction rose from 2.11% to 5.23%, the average particle size grew from 0.17 to 0.71 μm, and the high-angle grain boundary (HAGB > 15°) fraction declined from 67.5% to 52.2%. These microstructural alterations collectively caused the Charpy impact energy of the CGHAZ to decrease from 269 J to 48 J. The deterioration in toughness is primarily attributed to blocky M-A constituents lowering the resistance to crack nucleation and the reduced HAGB fraction diminishing the resistance to crack propagation. This work provides a theoretical foundation for optimizing the performance of X70 pipeline steel welded joints, and it is recommended that the nitrogen content in the base metal be strictly maintained below 0.005 wt% to ensure superior CGHAZ toughness. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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26 pages, 6836 KB

Open AccessArticle

Corrosion, Microstructural Evolution and Non-Destructive Monitoring of High-Strength Low-Alloy Steels Under Multiparametric Marine Exposure

by Polyxeni Vourna, Pinelopi P. Falara, Aphrodite Ktena, Evangelos V. Hristoforou and Nikolaos D. Papadopoulos

Metals 2026, 16(3), 270; https://doi.org/10.3390/met16030270 - 28 Feb 2026

Viewed by 592

Abstract

High-strength low-alloy (HSLA) steels in marine environments suffer from microbiologically influenced corrosion (MIC) and hydrogen-assisted degradation. This study investigates the synergistic effects of sulfate-reducing bacterial biofilms, mechanical stress, and seawater chemistry on HSLA AH36 steel using electrochemical, microstructural, and magnetic Barkhausen noise (MBN) [...] Read more.

High-strength low-alloy (HSLA) steels in marine environments suffer from microbiologically influenced corrosion (MIC) and hydrogen-assisted degradation. This study investigates the synergistic effects of sulfate-reducing bacterial biofilms, mechanical stress, and seawater chemistry on HSLA AH36 steel using electrochemical, microstructural, and magnetic Barkhausen noise (MBN) monitoring. Under multiparametric exposure (80% yield strength tensile stress, Desulfovibrio vulgaris, 28 days), biotic samples exhibited sustained 1.88× corrosion acceleration despite 86% sulfate depletion. Magnetic Barkhausen noise RMS amplitude (MBN_RMS) peaked at day 7 (612 ± 38 mV/mm) at pit depths of only 20–50 μm, detecting subsurface hydrogen damage before macroscopic failure. Quantitative correlations (R² ≥ 0.99) between MBN_RMS and cumulative mass loss revealed distinctive linear relationships in abiotic conditions and nonlinear cubic polynomials in biotic conditions, providing a non-destructive signature diagnostic of hydrogen-assisted MIC. Directional anisotropy analysis (parallel vs. perpendicular fields) showed that hydrogen-induced damage produces isotropic magnetic signatures (anisotropy ratio: 1.27 → 1.15), enabling discrimination between hydrogen embrittlement and stress-controlled degradation. The integration of portable MBN measurements with electrochemical monitoring establishes a quantitative framework for real-time structural health assessment and predictive maintenance of HSLA steels in maritime applications. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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17 pages, 6119 KB

Open AccessArticle

The Influence of Annealing on Microstructure Evolution and Mechanical Properties of 442 Ferritic Stainless Steel

by Yufeng Li, Changbo Wang, Yang Hui, Chen Chen, Xuefeng Lu, Jie Sheng and Xingchang Tang

Metals 2026, 16(2), 167; https://doi.org/10.3390/met16020167 - 30 Jan 2026

Viewed by 471

Abstract

The microstructure evolution law and the changes in mechanical properties of 442 ferritic stainless steel after annealing treatment at different temperatures are systematically investigated. The results show that, as the annealing temperature increases, the cold-rolled 442 ferritic stainless steel successively undergoes the process [...] Read more.

The microstructure evolution law and the changes in mechanical properties of 442 ferritic stainless steel after annealing treatment at different temperatures are systematically investigated. The results show that, as the annealing temperature increases, the cold-rolled 442 ferritic stainless steel successively undergoes the process of recovery, recrystallization and grain growth, with the microstructure gradually changing from a fibrous to recrystallized structure, and the secondary phases, such as the Nb(C, N) phase, σ phase and Laves phase, precipitate. In terms of mechanical properties, the tensile strength, yield strength and Vickers hardness gradually decrease, while the elongation after fracture gradually increases. When the annealing temperature reaches 800 °C, the material exhibits the optimal comprehensive mechanical properties. The yield strength, tensile strength and elongation reach 371 MPa, 534 MPa and 31%, respectively, and the hardness is 175 HV. The fracture mode of the sample is mainly ductile fracture. EBSD analysis indicates that the strong Brass {110}<112> texture existing in the cold-rolled state gradually weakens with the annealing process, and the {111}<110> texture strengthens, thereby reducing the influence of unfavorable textures. The research results provide theoretical basis and data support for microstructure regulation and performance optimization of 442 ferritic stainless steel. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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17 pages, 3251 KB

Open AccessArticle

Determination of Final Ferrite Grain Size During Multiple-Stage Controlled Cooling of Low-Carbon, Low-Alloy Steels

by Nathan Dixon, Carl Slater, Jinlong Du and Claire Davis

Metals 2025, 15(9), 956; https://doi.org/10.3390/met15090956 - 28 Aug 2025

Cited by 1 | Viewed by 1406

Abstract

Ferrite grain size strengthening makes the predominant contribution to the overall strength of ferrite–pearlite structural hollow section steel grades. A fine ferrite grain size is achieved through a two-stage controlled cooling process. First, the material is rapidly cooled with water. This provides a [...] Read more.

Ferrite grain size strengthening makes the predominant contribution to the overall strength of ferrite–pearlite structural hollow section steel grades. A fine ferrite grain size is achieved through a two-stage controlled cooling process. First, the material is rapidly cooled with water. This provides a large undercooling, which is the driving force for ferrite to form. The second stage involves slow natural (air) cooling, where the cooling rates and the transition temperature from water to air cooling are carefully controlled. This is crucial to prevent the formation of bainite or martensite. Ferrite grain sizes can be predicted for continuous cooling and isothermal transformation based on the prior austenite grain size, composition and cooling rate/isothermal transformation temperature. However, predictions for multiple-cooling-stage transformations have not been reported. In this work, EN S355-grade steel was used to study ferrite grain size development during continuous cooling, isothermal holding and complex (two-stage or multi-stage) cooling. Dilatometry and microstructure assessment was used to study the relationship between the final ferrite grain size and undercooling at which 40% of the ferrite formed. It was found that any changes in cooling rate/temperature (including a possible ‘bounce back’ in temperature due to latent heat formation) after 40% of the ferrite had formed had a negligible effect on the final ferrite grain size, assuming that re-austenitization or bainite formation was avoided. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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13 pages, 7792 KB

Open AccessArticle

Evolution of the Heterogeneous Microstructure of a 12Cr1MoV Welded Joint after Post-Weld Heat Treatment and Its Effect on Mechanical Properties

by Bin Yang, Guanghua Sun, Xiaodong Hu, Zichen Liu, Xuefang Xie, Wei Peng and Xiaoming Shao

Metals 2023, 13(12), 1998; https://doi.org/10.3390/met13121998 - 12 Dec 2023

Cited by 3 | Viewed by 2269

Abstract

The non-uniformity of microstructures and mechanical properties across a whole welded joint is a crucial factor leading to its weakening performance and premature failure. Post-weld heat treatment is a primary method for increasing the mechanical properties. However, the evolution mechanism of mechanical properties [...] Read more.

The non-uniformity of microstructures and mechanical properties across a whole welded joint is a crucial factor leading to its weakening performance and premature failure. Post-weld heat treatment is a primary method for increasing the mechanical properties. However, the evolution mechanism of mechanical properties related to heterogeneous microstructure after heat treatment remains unclear, making it challenging to design the heat treatment process and evaluate its effect comprehensively. In this study, microstructure characterization and a series of mechanical tests of 12Cr1MoV welded joint after the stress relief annealing (SRA) and tempering heat treatment (THT) were conducted. The effect of heat treatment on mechanical properties is analyzed based on the comparison between stress relief annealing and tempering heat treatment in terms of tensile properties, impact toughness, and impact fracture morphology. The results indicate that, after the tempering heat treatment, the evolution of mechanical properties in each subzone of the joint is consistent, i.e., the hardness and tensile strength decreased while the toughness increased. Notably, the most substantial enhancement in toughness is observed in the weld zone, primarily due to a significant reduction in the presence of pre-eutectoid ferrite. Furthermore, it is proved that hardness is an indicator to reflect changes in tensile strength related to the microstructure evolution, which indicates it can be employed to evaluate the effectiveness of post-weld heat treatment in practical engineering. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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14 pages, 4936 KB

Open AccessArticle

Deep Learning-Based Understanding of Defects in Continuous Casting Product

by Zeyuan Ding, Jingxiao Zhao, Raja Devesh Kuma Misra, Fujian Guo, Zhenjia Xie, Xuelin Wang, Xiucheng Li, Jingliang Wang and Chengjia Shang

Metals 2023, 13(11), 1809; https://doi.org/10.3390/met13111809 - 27 Oct 2023

Cited by 6 | Viewed by 3778

Abstract

A novel YOLOv5 network is presented in this paper to quantify the degree of defects in continuously cast billets. The proposed network addresses the challenges posed by noise or dirty spots and different defect sizes in the images of these billets. The CBAM-YOLOv5 [...] Read more.

A novel YOLOv5 network is presented in this paper to quantify the degree of defects in continuously cast billets. The proposed network addresses the challenges posed by noise or dirty spots and different defect sizes in the images of these billets. The CBAM-YOLOv5 network integrates the channel and spatial attention of the Convolutional Block Attention Module (CBAM) with the C3 layer of the YOLOv5 network structure to better fuse channel and spatial information, with focus on the defect target, and improve the network’s detection capability, particularly for different levels of segregation. As a result, the feature pyramid is improved. The feature map obtained after the fourth down-sampling of the backbone network is fed into the feature pyramid through CBAM to improve the perceptual field of the target and reduce information loss during the fusion process. Finally, a self-built dataset of continuously cast billets collected from different sources is used, and several experiments are conducted using this database. The experimental results show that the average accuracy (mAP) of the network is 93.7%, which can achieve intelligent rating. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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13 pages, 12715 KB

Open AccessArticle

The Influence of 1 wt.% Cr on the Corrosion Resistance of Low-Alloy Steel in Marine Environments

by Jianzhuo Gao, Ningxi Wang, Hui Chen and Xuexu Xu

Metals 2023, 13(6), 1050; https://doi.org/10.3390/met13061050 - 30 May 2023

Cited by 10 | Viewed by 3114

Abstract

In this study, the effects of 1 wt.% Cr addition on the corrosion behavior and mechanisms of low-alloy structural steel in a marine environment were investigated through immersion experiments, corrosion product analysis, and electrochemical experimental systems. The results demonstrate that the addition of [...] Read more.

In this study, the effects of 1 wt.% Cr addition on the corrosion behavior and mechanisms of low-alloy structural steel in a marine environment were investigated through immersion experiments, corrosion product analysis, and electrochemical experimental systems. The results demonstrate that the addition of 1 wt.% Cr significantly enhances the corrosion resistance of low-alloy steel in marine environments. The influence of Cr addition on the corrosion product layer was analyzed through rust layer morphology, cross-sectional morphology, elemental distribution, and electrochemical systems. Cr addition effectively promotes the densification of the corrosion product layer on the surface of low-alloy steel in marine environments, hindering the penetration of corrosive ions and thus improving corrosion resistance. This study’s findings can promote the optimization of corrosion resistance in low-alloy steel in marine environments and enhance its application prospects in marine environments. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels (2nd Edition))

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