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Phase Transformation and Microstructure Evolution in Stainless Steels

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Metals and Alloys".

Deadline for manuscript submissions: closed (10 December 2022) | Viewed by 28199

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Dr. Javad Mola

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Materials Design and Structural Integrity Laboratory, Faculty of Engineering and Computer Sciences, Osnabrück University of Applied Sciences, 49076 Osnabrück, Germany
Interests: metallic materials; phase transformations; mechanical properties; microstructure characterization; segregation and partitioning phenomena

Special Issue Information

Dear Colleagues,

Although all stainless steels can be classified as either ferritic or austenitic depending on their solidification mode, they undergo a variety of phase transformations in the solid state leading to the major classes of austenitic, ferritic, duplex, and martensitic stainless steels with a wide variety of properties.

The current Special Issue is focused on research results involving an analysis of phase transformations and/or mechanical properties in stainless steels. Phase transformations may have been induced either by thermal or mechanical treatment. Of particular interest is the deformation-induced microstructure evolution of the austenite constituent in fully or partially austenitic stainless steels. The microstructure evolution may have occurred under laboratory conditions or during industrial production and/or service. Ideally, the microstructural evolution is correlated with the properties and performance. Submissions making use of theoretical approaches and simulation tools, for instance, thermodynamic and kinetic calculations, or those contributing to the critical assessment of such databases also fit within the scope of this Special Issue.

With your contributions, this Special Issue will offer solutions to some of the existing problems with stainless steels and promote the state-of-the-art on stainless steels.

Dr. Javad Mola
Guest Editor

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Keywords

stainless steels
phase transformations
properties
deformation-induced processes
precipitates
microstructure characterization
microstructure modeling

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Published Papers (9 papers)

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Research

20 pages, 8403 KiB

Open AccessArticle

Microstructural Constituents and Mechanical Properties of Low-Density Fe-Cr-Ni-Mn-Al-C Stainless Steels

by Steffen Scherbring, Guanghui Chen, Bastian Veltel, Gert Bartzsch, Julia Richter, Malte Vollmer, Malte Blankenburg, Saikat Shyamal, Olena Volkova, Thomas Niendorf, Ulrich Lienert, Puspendu Sahu and Javad Mola

Materials 2022, 15(15), 5121; https://doi.org/10.3390/ma15155121 - 23 Jul 2022

Cited by 7 | Viewed by 2515

Abstract

Metallic material concepts associated with the sustainable and efficient use of resources are currently the subject of intensive research. Al addition to steel offers advantages in view of lightweight, durability, and efficient use of high-Fe scrap from the Al industry. In the present work, Al was added to Fe-12Cr-(9,12)Ni-3Mn-0.3C-xAl (x = 0.1–6) (wt.%) stainless steels to assess its influence on microstructure and mechanical properties. According to density measurements based on Archimedes’ principle, densities were between 7.70 and 7.08 g/cm³. High-energy X-ray diffraction estimations of the lattice parameter indicated that nearly 31% of density reduction was caused by the lattice expansion associated with Al addition. Depending on Al concentration, austenitic and duplex matrix microstructures were obtained at room temperature. In the presence of up to 3 wt.% Al, the microstructure remained austenitic. At the same time, strength and hardness were slightly enhanced. Al addition in higher quantities resulted in the formation of duplex matrix microstructures with enhanced yield strength but reduced ductility compared to the austenitic alloys. Due to the ready formation of B2-(Ni,Fe)Al intermetallics in the ferrite phase of the present alloy system, the increase in strength due to the presence of ferrite was more pronounced compared to standard duplex stainless steels. The occurrence of B2 intermetallics was implied by dilatometry measurements and confirmed by electron microscopy examinations and high-energy X-ray diffraction measurements. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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13 pages, 1529 KiB

Open AccessArticle

The Effect of Severe Shot Peening on Fatigue Life of Laser Powder Bed Fusion Manufactured 316L Stainless Steel

by Timo Rautio, Matias Jaskari, Tejas Gundgire, Terho Iso-Junno, Minnamari Vippola and Antti Järvenpää

Materials 2022, 15(10), 3517; https://doi.org/10.3390/ma15103517 - 13 May 2022

Cited by 28 | Viewed by 3403

Abstract

Severe shot peening (SSP) was used on additive manufactured 316L by laser powder bed fusion. The effect of the post processing on the surface features of the material was analyzed through residual stress measurements, tensile testing, hardness-depth profiles, and fatigue testing by flexural bending. The results showed that SSP can be utilized to form residual stresses up to −400 MPa 200 μm below the surface. At the same time, a clear improvement on the surface hardness was achieved from 275 HV to near 650 HV. These together resulted in a clear improvement on material strength which was recorded at 10% improvement in ultimate tensile strength. Most significantly, the fatigue limit of the material was tripled from 200 MPa to over 600 MPa and the overall fatigue strength raised similarly from a low to high cycle regime. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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18 pages, 5918 KiB

Open AccessArticle

Influence of C and N on Strain-Induced Martensite Formation in Fe-15Cr-7Mn-4Ni-0.5Si Austenitic Steel

by Caroline Quitzke, Qiuliang Huang, Horst Biermann, Olena Volkova and Marco Wendler

Materials 2021, 14(21), 6502; https://doi.org/10.3390/ma14216502 - 29 Oct 2021

Cited by 13 | Viewed by 2278

Abstract

In this study, the effect of interstitial contents on the mechanical properties and strain-induced martensite formation in an austenitic stainless steel was investigated. The mechanical properties of solution annealed Fe-15Cr-7Mn-4Ni-0.5Si-(0.01-0.2)N-(0.01-0.2)C concentrations in weight percent stainless steels were studied using room temperature tensile tests. All three alloys used in the present study have a sum content of C + N of about 0.2 wt.%. To verify the influence of C and N on deformation behavior, microstructural investigations are performed using light optical microscopy, scanning electron microscopy, and magnetic and hardness measurements. Moreover, strain-induced α′-martensite nucleation was characterized by scanning electron microscope using EBSD. In the present alloy system, carbon provides a stronger austenite stabilizing effect than nitrogen. Hence, the smallest amount of strain-induced α′-martensite was formed in the steel alloyed with 0.2 wt.% C. It also exhibited the optimal mechanical properties, including the highest ultimate tensile strength (1114 MPa), uniform elongation (63%), and total elongation (68%). Moreover, the interstitial content influences the occurrence of dynamic strain aging (DSA), which was only observed in the steel alloyed with carbon. With increasing C content, the triggering strain for DSA decreases, which can be confirmed by in situ magnetic measurements during tensile testing. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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15 pages, 5997 KiB

Open AccessArticle

Tensile Properties and Deformation of AISI 316L Additively Manufactured with Various Energy Densities

by Matias Jaskari, Sumit Ghosh, Ilkka Miettunen, Pentti Karjalainen and Antti Järvenpää

Materials 2021, 14(19), 5809; https://doi.org/10.3390/ma14195809 - 4 Oct 2021

Cited by 20 | Viewed by 3247

Abstract

Additive manufacturing (AM) is an emerging fabrication technology that offers unprecedented potential for manufacturing end-to-end complex shape customized products. However, building products with high performance by AM presents a technological challenge. Inadequate processing parameters, fabrication environment or changes in powder properties may lead to high defect density in the part and poor mechanical properties. Microstructure, defect structure, and mechanical properties of AISI 316L stainless steel pieces, additively manufactured by the laser powder bed fusion method using three different volume energy densities (VEDs), were investigated and compared with those of a commercial wrought AISI 316L sheet. Scanning and transmission electron microscopies were employed for characterization of grain and defect structures, and mechanical properties were determined by tensile testing. It was found that the number of defects such as pores and lack of fusion in AM specimens did not affect the strength, but they impaired the post-uniform elongation, more significantly when processed with the low VED. Twinning was found to be an active deformation mechanism in the medium and high VED specimens and in the commercially wrought material in the later stage of straining, but it was suppressed in the low VED specimens presumably because the presence of large voids limited the strain attained in the matrix. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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15 pages, 7928 KiB

Open AccessArticle

by Mikko Hietala, Matias Jaskari, Mohammed Ali, Antti Järvenpää and Atef Hamada

Materials 2021, 14(19), 5580; https://doi.org/10.3390/ma14195580 - 26 Sep 2021

Cited by 17 | Viewed by 2906

Abstract

In this study, ultra-high-strength steels, namely, cold-hardened austenitic stainless steel AISI 301 and martensitic abrasion-resistant steel AR600, as base metals (BMs) were butt-welded using a disk laser to evaluate the microstructure, mechanical properties, and effect of post-weld heat treatment (PWHT) at 250 °C of the dissimilar joints. The welding processes were conducted at different energy inputs (EIs; 50–320 J/mm). The microstructural evolution of the fusion zones (FZ) in the welded joints was examined using electron backscattering diffraction (EBSD) and laser scanning confocal microscopy. The hardness profiles across the weldments and tensile properties of the as-welded joints and the corresponding PWHT joints were measured using a microhardness tester and universal material testing equipment. The EBSD results showed that the microstructures of the welded joints were relatively similar since the microstructure of the FZ was composed of a lath martensite matrix with a small fraction of austenite. The welded structure exhibited significantly higher microhardness at the lower EIs of 50 and 100 J/mm (640 HV). However, tempered martensite was promoted at the high EI of 320 J/mm, significantly reducing the hardness of the FZ to 520 HV. The mechanical tensile properties were considerably affected by the EI of the as-welded joints. Moreover, the PWHT enhanced the tensile properties by increasing the deformation capacity due to promoting the tempered martensite in the FZ. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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22 pages, 8841 KiB

Open AccessArticle

Microstructure Evolution and Mechanical Properties of X6CrNiMoVNb11-2 Stainless Steel after Heat Treatment

by Jia Fu and Chaoqi Xia

Materials 2021, 14(18), 5243; https://doi.org/10.3390/ma14185243 - 12 Sep 2021

Cited by 5 | Viewed by 3456

Abstract

X6CrNiMoVNb11-2 supermartensitic stainless steel, a special type of stainless steel, is commonly used in the production of gas turbine discs in liquid rocket engines and compressor disks in aero engines. By optimizing the parameters of the heat-treatment process, its mechanical properties are specially adjusted to meet the performance requirement in that particular practical application during the advanced composite casting-rolling forming process. The relationship between the microstructure and mechanical properties after quenching from 1040 °C and tempering at 300–670 °C was studied, where the yield strength, tensile strength, elongation and impact toughness under different cooling conditions are obtained by means of mechanical property tests. A certain amount of high-density nanophase precipitation is found in the martensite phase transformation through the heat treatment involved in the quenching and tempering processes, where M₂₃C₆ carbides are dispersed in lamellar martensite, with the close-packed Ni₃Mo and Ni₃Nb phases of high-density co-lattice nanocrystalline precipitation created during the tempering process. The ideal process parameters are to quench at 1040 °C in an oil-cooling medium and to temper at 650 °C by air-cooling; final hardness is averaged about 313 HV, with an elongation of 17.9%, the cross-area reduction ratio is 52%, and the impact toughness is about 65 J, respectively. Moreover, the tempered hardness equation, considering various tempering temperatures, is precisely fitted. This investigation helps us to better understand the strengthening mechanism and performance controlling scheme of martensite stainless steel during the cast-rolling forming process in future applications. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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24 pages, 7423 KiB

Open AccessArticle

Influence of Carbon on the Microstructure Evolution and Hardness of Fe–13Cr–xC (x = 0–0.7 wt.%) Stainless Steel

by Michael Harwarth, Adam Brauer, Qiuliang Huang, Mehdi Pourabdoli and Javad Mola

Materials 2021, 14(17), 5063; https://doi.org/10.3390/ma14175063 - 4 Sep 2021

Cited by 8 | Viewed by 2689

Abstract

The influence of carbon on the phase transformation behavior of stainless steels with the base chemical composition Fe–13Cr (wt.%), and carbon concentrations in the range of 0–0.7 wt.%, was studied at temperatures between −196 °C and liquidus temperature. Based on differential scanning calorimetry (DSC) measurements, the solidification mode changed from ferritic to ferritic–austenitic as the carbon concentration increased. The DSC results were in fair agreement with the thermodynamic equilibrium calculation results. In contrast to alloys containing nearly 0% C and 0.1% C, alloys containing 0.2–0.7% C exhibited a fully austenitic phase stability range without delta ferrite at high temperatures. Quenching to room temperature (RT) after heat treatment in the austenite range resulted in the partial transformation to martensite. Due to the decrease in the martensite start temperature, the fraction of retained austenite increased with the carbon concentration. The austenite fraction was reduced by cooling to −196 °C. The variation in hardness with carbon concentration for as-quenched steels with martensitic–austenitic microstructures indicated a maximum at intermediate carbon concentrations. Given the steady increase in the tetragonality of martensite at higher carbon concentrations, as confirmed by X-ray diffraction measurements, the variation in hardness with carbon concentration is governed by the amount and stability of austenite. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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26 pages, 42000 KiB

Open AccessArticle

Constitutive Descriptions and Restoration Mechanisms of a Fe-17Cr Alloy during Deformation at Temperatures of 700–1000 °C

by Fei Gao, Zilong Gao, Qiyong Zhu and Zhenyu Liu

Materials 2021, 14(17), 5022; https://doi.org/10.3390/ma14175022 - 3 Sep 2021

Cited by 3 | Viewed by 2095

Abstract

The deformation behavior for highly purified Fe-17Cr alloy was investigated at 700~1000 °C and 0.5~10 s⁻¹. The microstructure evolution and corresponding mechanism during deformation were studied in-depth, using electron backscattering diffraction, transmission electron microscopy and precession electron diffraction. During deformation, dynamic recrystallization (DRX) occurred, along with extensive dynamic recovery, and the active DRX mechanism depended on deformation conditions. At higher Zener-Hollomon parameter (Z ≥ 5.93 × 10²⁷ s⁻¹), the development of the shear band was promoted, and then continuous DRX was induced by the formation and intersection shear band. At lower Zener-Hollomon parameter (Z ≤ 3.10 × 10²⁵ s⁻¹), the nucleation of the new grain was attributed to the combination of continuous DRX by uniform increase in misorientation between subgrains and discontinuous DRX by grain boundary bulging, and with increasing temperature, the effect of the former became weaker, whereas the effect of the latter became stronger. The DRX grain size increased with the temperature. For alleviating ridging, it seems advantageous to activate the continuous DRX induced by shear band through hot deformation with higher Z. In addition, the modified Johnson-Cook and Arrhenius-type models by conventional way were developed, and the modified Johnson-Cook model was developed, using the proposed way, by considering strain dependency of the material parameters. The Arrhenius-type model was also modified by using the proposed way, through distinguishing stress levels for acquiring partial parameter and through employing peak stress to determine the activation energy and considering strain dependency of only other parameters for compensating strain. According to our comparative analyses, the modified Arrhenius-type model by the proposed approach, which is suggested to model hot-deformation behavior for metals having only ferrite, could offer a more accurate prediction of flow behavior as compared to other developed models. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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27 pages, 18551 KiB

Open AccessArticle

Phase Transformation in 316L Austenitic Steel Induced by Fracture at Cryogenic Temperatures: Experiment and Modelling

by Kinga Nalepka, Błażej Skoczeń, Marlena Ciepielowska, Rafał Schmidt, Jakub Tabin, Elwira Schmidt, Weronika Zwolińska-Faryj and Robert Chulist

Materials 2021, 14(1), 127; https://doi.org/10.3390/ma14010127 - 30 Dec 2020

Cited by 16 | Viewed by 3617

Abstract

Investigations by electron backscatter diffraction (EBSD) and X-ray diffraction with the use of synchrotron radiation, as well as parallel extended finite element (XFEM) simulations, reveal the evolution of the 316L stainless steel microstructure in the vicinity of a macro-crack developing at the temperature of liquid helium (4.2 K). The fracture propagation induces a dynamic, highly localized phase transformation of face-centred cubic austenite into α’ martensite with a body-centred cubic structure. Synchrotron studies show that the texture of the primary phase controls the transition process. The austenite grains, tending to the stable Brass orientation, generate three mechanisms of the phase transformation. EBSD studies reveal that the secondary phase particles match the ordered austenitic matrix. Hence, interphase boundaries with the Pitsch disorientation are most often formed and α’ martensite undergoes intensive twinning. The XFEM simulations, based on the experimentally determined kinetics of the phase transformation and on the relevant constitutive relationships, reveal that the macro-crack propagates mainly in the martensitic phase. Synchrotron and EBSD studies confirm the almost 100% content of the secondary phase at the fracture surface. Moreover, they indicate that the boundaries formed then are largely random. As a result, the primary beneficial role of martensite as reinforcing particles is eliminated. Full article

(This article belongs to the Special Issue Phase Transformation and Microstructure Evolution in Stainless Steels)

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