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Showing papers on "Austenite published in 2020"


Journal ArticleDOI
TL;DR: In this paper, an overview of the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications.
Abstract: Today, a large number of different steels are being processed by Additive Manufacturing (AM) methods. The different matrix microstructure components and phases (austenite, ferrite, martensite) and the various precipitation phases (intermetallic precipitates, carbides) lend a huge variability in microstructure and properties to this class of alloys. This is true for AM-produced steels just as it is for conventionally-produced steels. However, steels are subjected during AM processing to time-temperature profiles which are very different from the ones encountered in conventional process routes, and hence the resulting microstructures differ strongly as well. This includes a very fine and highly morphologically and crystallographically textured microstructure as a result of high solidification rates as well as non-equilibrium phases in the as-processed state. Such a microstructure, in turn, necessitates additional or adapted post-AM heat treatments and alloy design adjustments. In this review, we give an overview over the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications. This includes austenitic, duplex, martensitic and precipitation-hardening stainless steels, TRIP/TWIP steels, maraging and carbon-bearing tool steels and ODS steels. We identify areas with missing information in the literature and assess which properties of AM steels exceed those of conventionally-produced ones, or, conversely, which properties fall behind. We close our review with a short summary of iron-base alloys with functional properties and their application perspectives in Additive Manufacturing.

467 citations


Journal ArticleDOI
TL;DR: In this article, the transformation-induced plasticity (TRIP) in advanced high-strength steels (AHSS) is reviewed, where the main concepts and the recent progress in the processing and properties of AHSS are introduced.
Abstract: The transformation-induced plasticity (TRIP) in advanced high-strength steels (AHSS) is reviewed, where the main concepts and the recent progress in the processing and properties of AHSS are introduced. The metastable austenitic stainless and multiphase TRIP-assisted steels, as well as the more recent third generation AHSS grades, namely the medium-Mn and quenching and partitioning (Q&P) steels, are critically discussed. These steels utilize the TRIP effect and the enhanced work-hardening rate through the transformation of (retained) austenite in their microstructures to martensite during plastic deformation for the improvement of strength-ductility balance, which make them especially suitable for the automotive industry to be used in the lightweight car body for addressing the safety, fuel consumption, and air pollution issues. The kinetics of strain-induced martensitic transformation (SIMT) as well as the effects of chemical composition, grain size, deformation temperature, strain rate, and deformation mode on the austenite stability are reviewed. The effects of holding temperature and time during the isothermal bainitic transformation (IBT) in TRIP-aided steels, during the austenite-reverted-transformation (ART) annealing in medium-Mn steels, and during the quenching and partitioning steps in the Q&P steels are critically discussed towards enhancement of the amount of retained austenite and optimization of strength-ductility trade off. The alternative thermomechanical processing routes as well as the modified grades such as δ-TRIP and quenching-partitioning-tempering steels are also introduced.

254 citations


Journal ArticleDOI
TL;DR: In this paper, the microstructure and mechanical behavior of the dissimilar welded joint (DWJ) between ferritic-martensitic steel and austenitic grade steel along with its application have been summarized in Ultra Super Critical (USC) power plant.

126 citations


Journal ArticleDOI
TL;DR: In this article, the hierarchical martensitic features in ultra-high strength stainless steel (UHSSS), including the prior austenite grains, martensite packets, blocks and laths with the descending size, were refined to various extents by employing different thermomechanical processes and then carefully characterized.

115 citations


Journal ArticleDOI
TL;DR: In this article, the deformation-induced martensitic transformation, the transformation-induced plasticity (TRIP) effect, and the reversion annealing in the metastable austenitic stainless steels are reviewed.

110 citations


Journal ArticleDOI
TL;DR: In this article, the role of volumetric energy density on the microstructural evolution, texture and mechanical properties of 304L stainless steel parts additively manufactured via selective laser melting process is investigated.
Abstract: The role of volumetric energy density on the microstructural evolution, texture and mechanical properties of 304L stainless steel parts additively manufactured via selective laser melting process is investigated. 304L is chosen because it is a potential candidate to be used as a matrix in a metal matrix composite with nanoparticles dispersion for energy and high temperature applications. The highest relative density of 99 %±0.5 was achieved using a volumetric energy density of 1400 J/mm3. Both XRD analysis and Scheil simulation revealed the presence of a small trace of the delta ferrite phase, due to rapid solidification within the austenitic matrix of 304L. A fine cellular substructure ranged between 0.4–1.8 μm, was detected across different energy density values. At the highest energy density value, a strong texture in the direction of [100] was identified. At lower energy density values, multicomponent texture was found due to high nucleation rate and the existing defects. Yield strength, ultimate tensile strength, and microhardness of samples with a relative density of 99 % were measured to be 540 ± 15 MPa, 660 ± 20 MPa and 254 ± 7 HV, respectively and higher than mechanical properties of conventionally manufactured 304L stainless steel. Heat treatment of the laser melted 304L at 1200 °C for 2 h, resulted in the nucleation of recrystallized equiaxed grains followed by a decrease in microhardness value from 233 ± 3 HV to 208 ± 8 HV due to disappearance of cellular substructure.

101 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported a method to strengthen 316L stainless steel by adding 1-wt% and 3-twt% micron-sized particles using low energy ball milling for the powder feedstock preparation followed by selective laser melting (SLM).
Abstract: 316L austenitic stainless steel has a wide range of industrial applications. However, one of the major drawbacks is its low yield strength (170–300 MPa in annealed state). We report a method to strengthen 316L by adding 1 wt% and 3 wt% micron-sized TiC particles using low energy ball milling for the powder feedstock preparation followed by selective laser melting (SLM). The TiC particles were observed to be uniformly dispersed and well bonded to the 316L matrix after SLM. The 316L-TiC composites obtained were close to full density and the austenite grains were significantly refined with the addition of TiC particles. Tensile tests show that adding 1 wt% and 3 wt% TiC particles leads to a significantly increased yield strength (660 MPa and 832 MPa) and UTS (856 MPa and 1032 MPa) and maintains the good ductility (55% and 29% elongation). These findings offer a new perspective on the strengthening of 316L stainless steel

96 citations


Journal ArticleDOI
TL;DR: In this paper, a short overview of the opportunities that the conventional and innovative processing routes can offer for grain refinement of steels is presented, including thermal cycling, martensite process, and static recrystallization (SRX).
Abstract: Thermal mechanisms of microstructural refinement in steels were reviewed. These include thermal cycling, martensite process, and static recrystallization (SRX), in which the dominant stage of microstructural refinement is governed by an annealing treatment of a deformed or an undeformed material. Recent progress in grain refinement by thermal cycling for the body-centered cubic, face-centered cubic, and dual phase (DP) steels was introduced. The application of the cold rolling and subsequent annealing of a martensite starting structure (martensite process) for grain refinement of low-carbon and DP steels was reviewed. The formation and reversion of strain-induced martensite in metastable austenitic stainless steels and their effects on the microstructural evolutions were critically discussed. Moreover, the repetition of the martensite process and its limitations were explained. Important findings on the SRX of ferrite and austenite for grain refinement as well as the recrystallization kinetics were presented. Finally, the concepts of controlled rolling for grain refinement and the interaction of austenite recrystallization and strain-induced precipitation in microalloyed steels during thermomechanical processing were also reviewed. This short overview presents the opportunities that the conventional and innovative processing routes can offer for grain refinement of steels.

88 citations


Journal ArticleDOI
TL;DR: In this paper, the authors observed an abnormal transformation-induced plasticity (TRIP) effect in a 1500MPa Q&P steel and found that the dislocation density in the martensite matrix is suppressed at 1000 s−−1, resulting in a lower work hardening.

86 citations


Journal ArticleDOI
14 Feb 2020
TL;DR: In this paper, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the micro-structures, are reviewed.
Abstract: Martensitic stainless steels are widely used in industries due to their high strength and good corrosion resistance performance. Precipitation-hardened (PH) martensitic stainless steels feature very high strength compared with other stainless steels, around 3-4 times the strength of austenitic stainless steels such as 304 and 316. However, the poor workability due to the high strength and hardness induced by precipitation hardening limits the extensive utilization of PH stainless steels as structural components of complex shapes. Laser powder bed fusion (L-PBF) is an attractive additive manufacturing technology, which not only exhibits the advantages of producing complex and precise parts with a short lead time, but also avoids or reduces the subsequent machining process. In this review, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the microstructures, are reviewed. Then, the characteristics of defects in the as-built state and the causes are specifically analyzed. Afterward, the effect of process parameters and heat treatment conditions on mechanical properties are summarized and reviewed. Finally, the remaining issues and suggestions on future research on L-PBF of martensitic precipitation-hardened stainless steels are put forward.

77 citations


Journal ArticleDOI
Binhan Sun1, Waldemar Krieger1, Michael Rohwerder1, Dirk Ponge1, Dierk Raabe1 
TL;DR: In this article, the authors investigate two austenite-ferrite medium Mn steel samples with very different phase characteristics and observe that the two types of microstructures show very different response to HE, due to fundamental differences between the HE micromechanisms acting in them.

Journal ArticleDOI
TL;DR: In this article, the microstructure evolution and tensile properties of a newly designed Fe-21Mn-10Al-1C-5Ni (wt.%) lightweight steel subjected to two annealing conditions (inducing partial recrystallization and full re-stallization) and subsequent aging treatment have been investigated.

Journal ArticleDOI
TL;DR: In this paper, the effect of hydrogen charging on the microstructure and durability of traditional wrought and selective laser melted 316L stainless steels (SLMed 316L SSs) in a proton exchange membrane fuel cell was studied.

Journal ArticleDOI
TL;DR: In this article, the authors describe the distinct high cycle fatigue properties of advanced bainitic steels to elucidate the significant role of retained austenite with different morphologies on sub-surface fatigue crack initiation process.

Journal ArticleDOI
TL;DR: In this article, a novel austenite-martensite dual-phase steel with a ductility of 30% and tensile strength over 1.4 GPa was developed.

Journal ArticleDOI
21 Feb 2020
TL;DR: The reversion of deformation induced martensite to fine-grained austenite has been found to be an efficient method to increase significantly the yield strength of metastable austenitic stainless steels without impairing much their ductility.
Abstract: Strength properties of annealed austenitic stainless steels are relatively low and therefore improvements are desired for constructional applications. The reversion of deformation induced martensite to fine-grained austenite has been found to be an efficient method to increase significantly the yield strength of metastable austenitic stainless steels without impairing much their ductility. Research has been conducted during thirty years in many research groups so that the features of the reversion process and enhanced properties are reported in numerous papers. This review covers the main variables and phenomena during the reversion processing and lists the static and dynamic mechanical properties obtained in laboratory experiments, highlighting them to exceed those of temper rolled sheets. Moreover, formability, weldability and corrosion resistant aspects are discussed and finally the advantage of refined grain structure for medical applications is stated. The reversion process has been utilized industrially in a very limited extent, but apparently, it could provide a feasible processing route for strengthened austenitic stainless steels.

Journal ArticleDOI
TL;DR: In this paper, an austenitic stainless steel 316L part was fabricated by cold metal transfer wire and arc additive manufacturing (CMT-WAAM), and its microstructure, microhardness and tensile properties were investigated.
Abstract: An austenitic stainless steel 316L part was fabricated by cold metal transfer wire and arc additive manufacturing (CMT-WAAM), and its microstructure, microhardness and tensile properties were investigated. Results showed that the as-built 316L part exhibited a multilayered structure along the building direction. In the transverse direction (perpendicular to scanning direction) of each layer, there was also a multilayered structure of alternating overlapping zone (OA) and re-melting zone (RA). Compared with the OA, the RA had higher ferrite content, smaller austenite dendrite size, more dispersed orientation and lower residual stress. The overall multilayered structure and the intra-layer non-equilibrium microstructure exhibit a great influence on the mechanical properties of as-built 316L part. Along the building and transverse direction, the microhardness distribution in the OA was uniform, while the RA showed a trend of lower hardness in the middle and higher hardness on both sides of the RA layer. The effect of multilayered structure on tensile properties was stronger in the transverse direction than that in the building direction. The deformation feature was obviously inconsistent between the OA and RA. Local necking and fracture always occurred in the OA. Microvoids trended to initiate at silicate impurity particles, grow into large cracks, and finally lead to material failure during tension.

Journal ArticleDOI
TL;DR: In this article, the effect of different heat treatment cycles on the hardness and microstructure of a low carbon Fe-Cr-Ni-Al maraging stainless steel (with the brand name CX) was studied.
Abstract: Additive manufacturing of a low carbon Fe–Cr–Ni–Al maraging stainless steel (with the brand name CX) through the laser-powder bed fusion (LPBF) process is studied. Since the strength of this material is enhanced through precipitation hardening, the effect of different heat treatment cycles on the hardness and microstructure is assessed. The LPBF-CX is heat treated through a standard heat treatment procedure consisted of austenitization at 900 °C for 1 h followed by air cooling and aging at 530 °C for 3 h. Moreover, the effect of aging treatment (with no austenitization) on the as-built sample is studied. The microstructure of the as-built, austenitized-aged, and aged samples is studied using multiscale electron microscopy techniques. The as-built LPBF-CX consists of the typical lath martensitic structure and minor retained austenite. The martensite laths are featured by high dislocation density, with no evidence of precipitates. Austenitization-aging treatment shows a detrimental effect on the strength of LPBF-CX, due to martensite laths growth and retardation of precipitates evolution. Aging of the as-built LPBF-CX results in strength enhancement due to the evolution of nanometric and coherent β-NiAl precipitates, and martensite laths refinement. Moreover, the pre-existing dislocation networks play a key role in the strength of the aged material. The strength enhancement of the aged LPBF-CX is investigated through the fundamentals of alloy hardening.

Journal ArticleDOI
Zhiyuan Yu1, Yi Zheng1, Junmei Chen1, Chuanfeng Wu1, Jijin Xu1, Hao Lu1, Chun Yu1 
TL;DR: In this article, it was shown that the thermal history, porosity and microstructural evolution are dependent on the laser energy density and the roughness of top surface of the deposited layer and intralayer porosity decrease with increase of the laser remelting energy density.

Journal ArticleDOI
TL;DR: In this paper, a phase diagram including martensitic transition temperatures and austenite Curie temperatures is presented for Ni-Co-Mn-Ti all-d-metal Heusler alloys.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the mechanical and microstructural responses of a high manganese twinning induced plasticity (TWIP) steel at a low-temperature range (from 373 to 77 K) via in situ neutron diffraction qualification and correlative microscopy characterization.

Journal ArticleDOI
28 Jan 2020
TL;DR: A review of the formation and characteristics of the expanded austenite phase is presented in this paper, together with mechanical, fatigue, tribological and corrosion resistance properties of this phase, electric and magnetic properties, wettability and biocompatibility.
Abstract: Austenitic stainless steels are employed in many industrial fields, due to their excellent corrosion resistance, easy formability and weldability. However, their low hardness, poor tribological properties and the possibility of localized corrosion in specific environments may limit their use. Conventional thermochemical surface treatments, such as nitriding or carburizing, are able to enhance surface hardness, but at the expense of corrosion resistance, owing to the formation of chromium-containing precipitates. An effective alternative is the so called low temperature treatments, which are performed with nitrogen- and/or carbon-containing media at temperatures, at which chromium mobility is low and the formation of precipitates is hindered. As a consequence, interstitial atoms are retained in solid solution in austenite, and a metastable supersaturated phase forms, named expanded austenite or S phase. Since the first studies, dating 1980s, the S phase has demonstrated to have high hardness and good corrosion resistance, but also other interesting properties and an elusive structure. In this review the main studies on the formation and characteristics of S phase are summarized and the results of the more recent research are also discussed. Together with mechanical, fatigue, tribological and corrosion resistance properties of this phase, electric and magnetic properties, wettability and biocompatibility are overviewed.

Journal ArticleDOI
26 Apr 2020
TL;DR: In this article, the mechanical properties and microstructure of 304L austenitic stainless steel/Incoloy 800HT nickel alloy dissimilar welded joints are investigated and the joints were made of 21.3 mm × 7.47 mm tubes using the TIG process with the use of S Ni 6082 nickel filler metal.
Abstract: In this article, the mechanical properties and microstructure of 304L austenitic stainless steel/Incoloy 800HT nickel alloy dissimilar welded joints are investigated. The joints were made of 21.3 mm × 7.47 mm tubes using the TIG process with the use of S Ni 6082 nickel filler metal. No welding imperfections were found and high strength properties of joints were obtained, meeting the assumed acceptance criteria of the product’s standards. The tensile strength of the welded joints was higher than for the joined materials (Incoloy 800HT). Macro- and microscopic metallographic tests revealed the correct morphology of the joints and the appropriate structures in their critical zones. However, differences were found in the morphologies of the zones between the weld and the base materials. In fusion boundary from the side of the Incoloy 800HT alloy, no clear outline of the fusion line was observed (type A fusion boundary), while increased grain size and an epitaxial structure were observed. In turn, in the zone: weld–304L steel, a distinct fusion line was observed with areas with an increased amount of high-temperature δ ferrite (type B fusion boundary). No precipitates were found that could reduce the resistance of the joints to intergranular corrosion. A hardness decrease (approximately 30 HV0.1) in the transition zone: austenitic steel–weld and an increase of hardness (approximately 10 HV0.1) on the opposite side of the welded joint were observed.

Journal ArticleDOI
TL;DR: In this paper, a new precipitation hardening stainless steel (PHSS), C-X stainless steel, was manufactured using selective laser melting (SLM) technology, and a series of heat treatments were applied to improve the mechanical properties of the as-built samples.
Abstract: In this study, a new precipitation hardening stainless steel (PHSS), C-X stainless steel, was manufactured using selective laser melting (SLM) technology. Following SLM fabrication, a series of heat treatments were applied to improve the mechanical properties of the as-built samples. The microstructure precipitates distribution and evolution, and mechanical properties of SLM C-X stainless steels in the as-built and heat-treated conditions were systematically studied using scanning electron microscope (SEM), X-ray diffraction (XRD), and transmission electron microscope (TEM). The XRD spectrum revealed that solution treatment resulted in the formation of a complete martensite phase, and a reverted austenite (γ’) phase formed after aging treatment. The TEM analysis indicated that numerous dislocations and nanoprecipitates were dispersed within the martensite matrix for both the as-built and aged samples. The rod-like NiAl precipitates with a size range of 3–25 nm for the as-built samples and 7–30 nm for the solution-aged samples were determined through high-resolution TEM (HRTEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDS). Furthermore, the microhardness of the SLM C-X stainless steel parts was found to significantly improve from 350 HV0.2 in the as-built state to 510 HV0.2 in the solution-aged state. The ultimate tensile strength (UTS) of the SLM C-X stainless steel parts also increased from 1043 MPa in the as-built state to 1601 MPa after solution-aging heat treatment.

Journal ArticleDOI
TL;DR: In this article, the microstructural characteristics and mechanical properties of precipitation hardening (PH) stainless steel 15-5PH via Selective Laser Melting (SLM) were investigated.

Journal ArticleDOI
TL;DR: In this paper, the effect of heat treatment on mechanical and corrosion properties of SLM 15-5 Precipitation Hardening (PH) stainless steel was investigated to widen the application of additive manufacturing parts for industrial usages.

Journal ArticleDOI
TL;DR: In this paper, the microstructure and mechanical properties of 304 L stainless steel fabricated by selective laser melting are investigated, and a relative density of 99.9% is achieved with fine austenite grains and nanoscale cellular subgrains in size of approximately 0.5 µm.

Journal ArticleDOI
TL;DR: In this paper, powder-fed laser additive manufacturing (LAM) based on directed energy deposition (DED) technology is used to produce S316-L austenitic, and S410-L martensitic stainless steel structures by 3D-printing through a layer-upon-layer fashion.
Abstract: Powder-fed laser additive manufacturing (LAM) based on directed energy deposition (DED) technology is used to produce S316-L austenitic, and S410-L martensitic stainless steel structures by 3D-printing through a layer-upon-layer fashion. The microstructural features and crystallographic textural components are studied via electron backscattering diffraction (EBSD) analysis, hardness indentation and tensile testing. The results are compared with commercial rolled sheets of austenitic and martensitic stainless steels. A well-developed 200 > direction solidification texture (with a J-index of ∼11.5) is observed for the austenitic structure produced by the LAM process, compared to a J-index of ∼2.0 for the commercial austenitic rolled sheet. Such a texture in the LAM process is caused by equiaxed grain formation in the middle of each layer followed by columnar growth during layer-upon-layer deposition. A quite strong preferred orientation (J-index of 17.5) is noticed for martensitic steel developed by LAM. Large laths of martensite exhibit a dominant textural component of { 011 } 111 > in the α-phase, which is mainly controlled by transformation during layer-by-layer deposition. On the other hand, the martensitic commercial sheet consists of equiaxed grains without any preferred orientation or completely random orientations. In the case of the austenitic steel, mechanical properties such as tensile strength, hardness and ductility were severely deteriorated during the LAM deposition. A ductility loss of about 50% is recorded compared to the commercially rolled sheets that is attributed to the cast/solidified structure. However, LAM manufacturing of martensitic stainless steel structures leads to a considerably enhanced mechanical strength (more than double) at the expense of reduced ductility, because of martensitic phase transformations under higher cooling rates.

Journal ArticleDOI
TL;DR: In this article, a comprehensive study on the microstructure and mechanical properties of an additively manufactured 18Ni-300 maraging steel (with the brand name MS1), fabricated through the laser-powder bed fusion (LPBF) technique is presented.
Abstract: In this paper, a comprehensive study on the microstructure and mechanical properties of an additively manufactured 18Ni-300 maraging steel (with the brand name MS1), fabricated through the laser-powder bed fusion (LPBF) technique is presented. The influence of powder layer thickness and the characteristics of feedstock powder as the input in the LPBF process is investigated on the microstructure and mechanical properties of solid cubes and cylindrical rods. Relative density and hardness are measured through the depth of the manufactured cubes. The study of porosity and hardness through the depth of LPBF-MS1 cubes proves homogeneous properties in the core of the material in comparison with more heterogeneous properties closer to the subsurface layers. X-ray diffraction techniques both on the powder and the as-built samples are then performed to identify phases in the fabricated samples. A correlation between lower austenite content and higher strength is observed for the tensile samples manufactured with lower powder layer thickness. Texture analysis shows a directional grain growth along the building direction resulting in a weak texture, while the material induces a stronger texture with an increased amount of austenite after the deformation. Studying the effects of powder layer thickness shows slightly lower strength and ductility for the samples manufactured with higher powder layer thickness, while the energy consumption, as well as the manufacturing time, are reduced.

Journal ArticleDOI
TL;DR: In this article, the influence of rare earth (RE) contents on microstructure evolution and mechanical properties of pre-hardened mold steels was investigated through a series of experiments and theoretical analysis.