Austenite-martensite Transformation Research Articles

Structural Transformations in Duplex Stainless Steel CF8 Under Intensive Cold Plastic Deformation

The austenitic–martensitic transformation in austenitic–ferritic duplex stainless steel CF8 subjected to cold plastic deformation with a deformation degree ε = 10–95% is studied here using transmission Mössbauer spectroscopy (MS), conversion electron Mössbauer spectroscopy (CEMS), and X-ray diffraction (XRD) methods. It is assumed that the α′-martensite phase appeared at ε > 10%. The CEMS results showed that the formation of α′-martensite occurred most intensively in the near-surface layers of the steel, distributing in depth with the growth of the deformation degree. The volume fraction of the α′-martensite was determined based on the results of calculations carried out via the MS and XRD methods, and a good correlation was observed. A modified Olson–Cohen model was proposed to determine the dependence of the amount of α′-martensite on the deformation degree ε. The coefficients included in the Olson–Cohen expression were found.

Impact response of pseudoelastic nitinol

The response of polycrystalline nitinol with solely austenite structure was studied in three series of planar impact tests characterized by loading of the nitinol samples of 0.5–10 mm thickness by 1 mm thick aluminum impactor accelerated up to velocities of about 387, 429, and 567 m/s. In all the tests, the velocities of the free surfaces of the samples were monitored by a laser velocity interferometer. It was found that in all three test series, the amplitude of elastic precursor wave, being initially greater than 4 GPa, rapidly decays with the propagation distance down to ∼2.5 GPa, below which the decay is hindered by atomic clusters of the nanometer size. Based on the part of the velocity histories indicating the shock-induced austenite–martensite transformation, the initial, of about 2.5 × 103 s−1, and the maximum, up to 1 × 105 s−1, rates of the transformation were determined. As well, the impact stress slightly greater than 4 GPa was determined as that required for the onset of the B2 → B19′ transformation under shock loading. The unloading parts of the same velocity histories allowed a rough estimate of the fraction of the shock-transformed martensite and the elucidation of the virtually complete reversibility of the transformation.

Simultaneous enhancement of the strength and plasticity of Fe[sbnd]12Mn steel through modulating grain morphology

The relationship between grain morphology and tensile properties of Fe-12Mn steel thermo-mechanically processed by rolling annealing and re-cold rolling processes was investigated. The results indicated that the re-cold rolling deformed the mostly austenite grain morphology from equiaxed to lamellar, and the steel exhibited a yield strength of 1295 MPa, tensile strength of 1518 MPa, and elongation of 18 %. Compared to the experimental steel without re-cold rolling processes, more than 300 MPa tensile strength was improved and elongation increased from 14 % to 18 %. The steel demonstrated remarkable enhancement in mechanical properties owing to the “multistage TRIP effect”, which referred to the sequential martensitic phase transformation of austenite with varying stability as the strain increased. The change in grain morphology reduced the rate of twin formation and increased the nucleation point of the martensitic phase transition, this also stabilized the retained austenite by increasing the hard phases surrounding the retained austenite, which had multistage stability. These factors contributed to the “multistage TRIP effect”, which could be sustained to higher strains and presented regular fluctuations in work-hardening rates

A coupled crystal inelasticity-phase field model for crack growth in polycrystalline nitinol microstructures

Abstract This paper introduces a comprehensive computational framework, comprising a finite deformation crystal inelasticity constitutive model and phase field model, for modeling crack growth in superelastic nitinol polycrystalline microstructures. The crystal inelasticity model represents crystal stretching and lattice rotation from elastic mechanisms, as well as local inelastic deformation due to austenite-martensite phase transformation. The phase field formulation decomposes the Helmholtz free energy density into stored elastic energy, phase transformation energy, and crack surface energy components. The elastic energy accounts for tension-compression asymmetry with the formation of the crack through a spectral decomposition. Kinetic Monte Carlo simulations generate equilibrium area fractions of different surface orientations, which serve as weights for the surface energy. An adaptive wavelet-enhanced hierarchical finite element (FE) model is introduced to alleviate high computational overhead in phase field crack simulations. Simulations with the coupled inelasticity phase field model are conducted under various loading conditions including Mode-I tension, a quasi-static Kalthoff experiment, and cyclic loading of polycrystalline microstructures. Crack propagation is effectively predicted by this model, providing valuable insights into the material mechanical behavior with growing cracks.

Martensite-austenite transformation during dual-stage tempering and work-hardening characteristics of Mn–Ni–Mo steel

The reactor pressure vessel (RPV) in nuclear power plants is mainly made from Mn–Ni–Mo steel. After quenching, this steel's microstructure features martensite-austenite (M-A) islands. Tempering above 600 °C poses a challenge, as these islands can transform into harmful rod-like Fe3C precipitates, adversely affecting the RPV's tensile properties and structural integrity. This study explores the effects of M-A transformation during dual-stage tempering on the tensile properties of Mn–Ni–Mo steel, focusing on two austenite grain sizes (5 μm and 47 μm). The dual-stage tempering included a 2-h pre-tempering phase at temperatures between 200 °C and 500 °C, followed by a 3-h final tempering stage at 650 °C. Results showed that M-A transformation is temperature-dependent. At 200 °C, partial transformation led to rod-like Fe3C precipitates during final tempering, similar to direct tempering at 650 °C, reducing the critical stress for micro-crack nucleation and compromising tensile properties. Pre-tempering at 350 °C produced fine, aggregated precipitates that improved tensile strength by inhibiting dislocation movement. Conversely, pre-tempering at 500 °C resulted in coarser, more dispersed spherical precipitates. The Kocks-Mecking plot indicated that the 350 °C pre-tempered sample had the highest strain hardening capacity, with the strain hardening rate curve farthest from the origin and the shallowest slope during stage IV hardening. However, the 500 °C pre-tempered samples showed the best combination of elongation and strength.

Micro- and Macroscopic Analysis of Fatigue Wear of Gear Wheel Top Layer-An Impact Analysis of Thermochemical Treatment.

Today, there are many diagnostic methods and advanced measurement techniques enabling the correct diagnosis and assessment of the type and degree of wear of cogwheels (gears, pumps, etc.). The present study presents an analysis of the surface defects of a cogwheel of an oil pump prototype (3PW-BPF-24). The test object operated for a certain number of hours under controlled operating and environmental parameters. The damage to the surface layer was caused by fatigue phenomena and previous thermo-chemical treatment. On the basis of the significant percentage share (~30%) of residual austenite in the volume of the diffusion layer, a hypothetical conclusion was drawn about the suboptimal parameters of the thermo-chemical treatment process (in relation to the chemical composition of the analyzed pinion). A large number of research studies indicate that the significant presence of residual austenite causes a decrease in tooth surface hardness, the initiation of brittle cracks, a sharp decrease in fatigue strength, an increase in brittleness and a tendency to develop surface layer cracks during operation. High-resolution 3D scans of randomly selected pitting defects were used in the detailed study of the present work. It was indicated that the analysis of the morphology of surface defects allowed some degree of verification of the quality of the heat/chemical treatment. The martensitic transformation of residual austenite under controlled (optimum) repeated heat treatment conditions could significantly improve the durability of the pinion (cogwheel). In the case analyzed, the preferred treatment was the low-temperature treatment. The paper concludes with detailed conclusions based on the microscopic and macroscopic investigations carried out.

A data-driven approach to model the martensitic transformation temperature in strain-induced metastable austenitic steels

Strain-induced metastable austenitic stainless steels form an important class of materials in metallurgical industries for their wide range of applications. These steels undergo austenite-martensite phase transformation at temperatures above martensite start temperature, Ms, at which martensite is formed on mechanical deformation, also known as the Md temperature. Md temperature depends on several factors related to the steel and is important from alloy design perspective. In the literature, there are quite a few equations based on composition of the steels for the prediction of Md temperature. However, it is well known that the transformation from austenite to martensite is dependent on the austenite grain size as well as deformation conditions i.e. strain, strain rate and temperature of deformation. In the present work, the role of those parameters has also been considered. The model is implemented using fourteen input parameters viz., composition, grain size, amount of strain, temperature of deformation, and strain rate. The architecture of the neural network model is optimized rigorously to predict the Md temperature on a par with actual value. It has been shown that grain size and strain rate have very negligible influence whereas strain and temperature of deformation have quite strong role. Md temperature is increased with increasing strain whereas the temperature of deformation shows opposite dependence on it. An empirical equation thus, has been established to calculate the Md temperature of a steel as a function of its composition, grain size, temperature of deformation and strain. The final optimized model is then deployed to predict the Md temperature of different steels and predictions are found to be in close agreement to the experimentally measured Md temperatures. The developed model is general and can be extended to include other parameters as well as various other steel alloys.

Topology Optimization of Shape Memory Alloy Actuators for Prescribed Two-Way Transforming Shapes

This paper proposes a new topology optimization formulation for obtaining shape memory alloy actuators which are designed with prescribed two-way transforming shapes. The actuation behaviors of shape memory alloy structures are governed by austenite-martensite phase transformations effected by thermal-mechanical loading processes; therefore, to realize the precise geometric shape variations of shape memory alloy actuators, traditional methods involve iteration processes including heuristic structural design, numerical predictions and experimental validation. Although advanced structural optimization methods such as topology optimization have been used to design three-dimensional (3D) shape memory alloy actuators, the maximization/minimization of quantities such as structural compliance or inaccurate stroke distances has usually been selected as the optimization objective to obtain feasible solutions. To bridge the gap between precise shape-morphing requirements and efficient shape memory alloy actuator designs, this paper formulates optimization criteria with quantitatively desired geometric shapes, and investigates the automatic designs of two-way prescribed shape morphing shape memory alloy structures based on the proposed topology optimization method. The super element method and adjoint method are used to derive the analytical sensitivities of the objective functions with respect to the design variables. Numerical examples demonstrate that the proposed method can obtain 3D actuator designs that have the desired two-way transforming shapes.

Significantly enhanced fatigue resistance and mechanisms of hypoeutectic Al-Si composite calibrated using trace in-situ nanocrystals

Fatigue resistance under extreme stress conditions is an important indicator to evaluate industrial application potential of Al-Si-Mg alloys, but their fatigue resistance is inherently weakened by large grain size, long-needle Si phases and coarse precipitates. This work reports significantly optimized microstructure configuration and fatigue resistance of hypoeutectic Al-Si composite optimized by the nanocrystallization products of a NiNbTi metallic glass. It was proved the in-situ NiTi (B2) nanocrystals can serve as the heterogeneous nucleation sites of α-Al and β-Mg2Si and the growth retarder of eutectic Si. Particularly, the optimized composite exhibited nearly 5 times and 6 times longer fatigue life than the unoptimized alloy at 120 MPa (60 Hz) and 240 MPa (20 Hz), respectively. The fatigue strength (N = 107) was increased by 21.7 % and 25.9 % at 60 Hz and 20 Hz, respectively. The α-Al refinement enhanced the resistance to fatigue crack initiation. The refinement and spheroidization of eutectic Si phases reduced stress concentration. Also, the austenite-martensite phase transformation of NiTi afforded more energy for precipitation. Refined β-Mg2Si and β'' phases were facilitated to interact with dislocations, improving the resistance to dislocation slip during cyclic strain through the dislocation shearing effect. This work provides a theoretical basis for the future development of Al-Si alloys and composites with excellent fatigue resistance for expanding their industrial application scope.

Influence of the Cooling Rate on Austenite Ordering and Martensite Transformation in a Non-Stoichiometric Alloy Based on Ni-Mn-In

The effect of the melt cooling rate on the atomic ordering of austenite and, as a consequence, on the martensitic transformation of a nonstoichiometric alloy of the Ni-Mn-In system has been studied. In situ TEM observations revealed differences in the mechanism of phase transformations of the alloy subjected to different cooling conditions. It is shown that during quenching a high density of antiphase boundaries (APB) is formed and the alloy is in the austenite–martensitic (10M and 14M) state up to a temperature of 120 K. In a slowly cooled alloy, a lower APB density is observed, and a two-stage transformation, L21/B2 → 10M → 14M, occurs in the range of 150–120 K.

Impact response of nitinol over 300–473 K temperature range

The response of plane-parallel 2 mm thick samples of 47.3Ni-52.7Ti alloy was studied in two series of planar impact tests at temperatures between 300 and 473 K and between 473 and 318 K (heating to 473 K followed by cooling). In two additional series, the samples of 0.4–4 mm thickness were tested at 300 and 338 K (after preheating up to 473 K). In all the tests, the samples were loaded by 1 mm thick copper impactors having velocities equal to 314 ± 2 m/s. The velocity of the rear sample surface was continuously monitored by a laser Doppler velocimeter. It was shown that substantial, by an order of magnitude, variation of Hugoniot elastic limit σHEL and compressive strength Y of the nitinol with temperature are caused by the martensite–austenite transformation and its reversal. The variation of the dynamic tensile (spall) strength σsp of the nitinol along the heating–cooling path was found similar to that of σHEL although the difference between σsp values of austenite and martensite, ∼20%, is much more modest than in the case of σHEL. The test series performed at constant temperatures with samples of different thicknesses allows one to conclude that the plastic deformation in shocked austenite is presumably realized by dislocation motion and multiplication controlled by phonon viscosity. In the shocked martensite, the plastic deformation mechanism at a stress lower than ∼0.3 GPa is likely a thermally activated combination of deformation twinning and slip of kinking dislocations.

Investigations on austenite stability and martensitic transformation kinetics of a medium Mn steel under different strain states

Martensitic transformation has received wide attention due to its significant role in improving mechanical properties of medium Mn steels. In this paper, three typical strain states in sheet metal forming, uniaxial tension, biaxial tension and plane strain states, were selected to investigate the effect of the strain state on martensitic transformation of a medium Mn steel at room temperature. The experimental results show that the austenite stability of the medium Mn steel is seriously strain state dependent. The sample deformed under the plane strain state exhibits the lowest austenite stability, while it progressively increases for biaxial tension and uniaxial tension states. The microstructural evolution and the strain partitioning behavior of the material are characterized. It is indicated that the strains in austenite under different deformation modes are quite different even though the overall deformation conditions are similar, which leads to different transformation rates of γ → α’ transformation. Besides, the ε-martensitic transformation that only generates under the plane strain state further decreases the austenite stability. A strain state dependent α’-martensitic transformation kinetics law is proposed that incorporates the effect of the stress triaxiality and Lode angle parameter, which provides a reasonable prediction of γ → α’ transformation in the medium Mn steel over a wide range of strain states.

Microstructure Evolution at Ni/Fe Interface in Dissimilar Metal Weld between Ferritic Steel and Austenitic Stainless Steel.

The formation and evolution of microstructures at the Ni/Fe interface in dissimilar metal weld (DMW) between ferritic steel and austenitic stainless steel were investigated. Layered martensitic structures were noted at the nickel-based weld metal/12Cr2MoWVTiB steel interface after welding and post-weld heat treatment (PWHT). The formation of the interfacial martensite layer during welding was clarified and its evolution during PWHT was discussed by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), focused ion beam (FIB), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), transmission kikuchi diffraction (TKD), phase diagrams, and theoretical analysis. In as-welded DMW, the Ni/Fe interface structures consisted of the BCC quenched martensite layer and the FCC partially mixed zone (PMZ), which was the result of inhomogeneous solid phase transformation due to the chemical composition gradient. During the PWHT process, the BCC interfacial microstructure further evolved to a double-layered structure of tempered martensite and quenched martensite newly formed by local re-austenitization and austenite-martensite transformation. These types of martensitic structures induced inhomogeneous hardness distribution near the Ni/Fe interface, aggravating the mismatch of interfacial mechanical properties, which was a potential factor contributing to the degradation and failure of DMW.

Effects of soaking temperature on the microstructure and mechanical properties of a medium Mn steel for hot/warm forming

The increasing demands for better crashworthiness of vehicles require structural components with excellent energy absorption performance and anti-intrusion resistance. Here, we explored the potential of using a medium Mn steel with a 10 wt.% Mn content for hot/warm forming with the aim to produce automotive components with improved strength–ductility combination. The soaking temperature was varied from 670 to 870 °C for tuning the microstructure and the resultant mechanical properties. It is found that a duplex microstructure consisting of ferrite with a high dislocation density and retained austenite with a volume fraction of 53.5% is formed at 720 °C, leading to an exceptional strength–ductility combination (yield strength: 1016 MPa; ultimate tensile strength: 1407 MPa; total elongation: 32.7%). The energy absorbed before fracture is 39.8 GPa·%, which is four times more than that of the widely-used 22MnB5 boron steel. On basis of the experimental results, the effects of soaking temperature on austenite reverse transformation, ferrite recrystallization and martensitic transformation are discussed in depth to provide guidance for optimizing the strength–ductility combination of medium Mn steels processed by hot/warm forming.

INFLUENCE OF THE THERMAL CONDITION OF STEEL ON THE TRANSFORMATION TEMPERATURES OF TWO CHROMIUM HOT-WORK TOOL STEELS

The influence of the thermal condition of the steel on the transformation temperatures of two chromium hot-work tool steels was investigated. The steels studied were in two different thermal states: the soft -annealed state and the hardened-and-tempered state. The soft-annealed condition, i.e., the fully annealed condition, is a thermal state of steels in which the matrix is ferritic, and the carbon is chemically bonded in spherical carbides. The hardened-and-tempered condition, on the other hand, means a fully hardened-and-tempered martensitic matrix with uniformly distributed (primary and secondary) carbides. The samples were analysed in a simultaneous thermal analyser (STA) using the differential scanning calorimetry (DSC) method to determine the transformation temperatures. We also performed calculations based on the CALPHAD method to obtain the equilibrium temperatures of the transformations. The aim of the study was to determine the influence of different thermal conditions of chromium hot-work tool steels on the transformation temperatures such as solidus/liquidus temperatures, eutectoid transformation temperatures (A1 and A3), austenite solidification temperature and martensite transformation start temperatures. Since DSC analysis also measures thermal influence, we were able to determine the energies absorbed during eutectoid transformation and melting (endothermic processes) and the energies released during the solidification of δ-ferrite and γ-austenite (exothermic processes), as well as the energies released during martensite transformation. It was found that hardening and tempering reduce both eutectoid transformation temperatures and that the solidification intervals are closer to those calculated. From an energetic point of view, hardening and tempering reduce the energies absorbed during melting.

Effects of additive manufacturing process parameters and heat treatment on texture evolution and variant selection during austenite-martensite transformation in 18%Ni-M350 maraging steel

Variant selection and texture evolution of 18%Ni M350 maraging steel produced by laser-based directed energy deposition (DED) additive manufacturing (AM) technology are investigated in this study. The effects of heat treatment and AM processing parameters, including energy area density (EAD), powder feed rate, and laser power, on variant selection and texture evolution are discussed. Theoretically, 24 martensite variants tend to be formed during a cubic-to-cubic transformation based on the Kurdjumov–Sachs orientation relationship. Identifying the preference of variants in a thermo-mechanical process can pave the way for tailoring the desired product texture. Grain graph and local neighbor voting algorithms using measured electron backscatter diffraction (EBSD) were employed to reconstruct the parent austenite grain structure in this study. Even though no evidence of global variant selection is found, the variant selection tends to take place locally in small parent grains of heat-treated samples. Strong rotated Copper 112110γ and Z 111110γ components are observed in the parent austenite phase of the low EAD sample after heat treatment due to a high degree of recrystallization and second-order twins. A Goss texture 110001α in child martensite transitioned from these strong components is also observed to be strongly derived from packet 3 of this sample. This finding indicates that some low-misorientation variants of packet 3 are more energetically favorable to develop in a heat-treated M350 alloy produced by a low EAD.

Features of the Heat Treatment of High Speed Steel

The aim of the study was to determine the optimal heat treatment for cast steel P6M5F3 to ensure an increase in impact strength, under conditions of impact loads (planing cutters), minimize carbide liquation and compare with the impact strength of powder steel P6M5F3-MP. For the study, the issue of quenching P6M5F3 steel by simultaneous tempering was considered in order to select optimal values of impact strength, since the reliability of the tool is provided along with high hardness and high impact strength, especially with intermittent turning. Intensive separation of alloying elements and carbon from the residual austenite during its recrystallization makes it possible to apply the proposed method for the efficient and rational use of high-speed steels operating under conditions of increased dynamic loads, which require increased toughness. An increase in the temperature of the martensitic transformation interval as a result of heating indicates a significant depletion of residual austenite with carbon and alloying components during the holding of samples at these temperatures. The proposed heat treatment of high-speed steel allows, unlike the known methods, to completely avoid the martensitic transformation of high-temperature austenite into lamellar martensite, which causes a noticeable decrease in the strength and viscosity of the steel.

In Situ Observation of the Grain Growth Behavior and Martensitic Transformation of Supercooled Austenite in NM500 Wear-Resistant Steel at Different Quenching Temperatures.

In situ observations of the austenite grain growth and martensite transformations in developed NM500 wear-resistant steel were conducted via confocal laser scanning high-temperature microscopy. The results indicated that the size of the austenite grains increased with the quenching temperature (37.41 μm at 860 °C → 119.46 μm at 1160 °C) and austenite grains coarsened at ~3 min at a higher quenching temperature of 1160 °C. Furthermore, a large amount of finely dispersed (Fe, Cr, Mn)3C particles redissolved and broke apart at 1160 °C, resulting in many large and visible carbonitrides. The transformation kinetics of martensite were accelerated at a higher quenching temperature (13 s at 860 °C → 2.25 s at 1160 °C). In addition, selective prenucleation dominated, which divided untransformed austenite into several regions and resulted in larger-sized fresh martensite. Martensite can not only nucleate at the parent austenite grain boundaries, but also nucleate in the preformed lath martensite and twins. Moreover, the martensitic laths presented as parallel laths (0~2°) based on the preformed laths or were distributed in triangles, parallelograms, or hexagons with angles of 60° or 120°.

The microstructure evolution and dimensional stability of TiC steel-bonded cemented carbide during stabilizing heat treatments

Stabilizing heat treatment is an ideal method to improve the performance of heat-strengthened steel-bonded cemented carbide for high-precision inertial instruments and some wear parts. In the present study, a TiC steel-bonded cemented carbide consisting of 35 wt% TiC hard phase and chromium‑molybdenum low alloy steel matrix was subjected to various stabilizing heat treatments, including annealing, quenching, tempering and thermal cooling cycling (TCC) treatments. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and electronic probe micro-analyzer (EPMA) were applied to analyze the phase characteristics and microstructure of the material. In addition, the influence of microstructure evolution on the magnetic properties and dimensional stability of the cemented carbide was also investigated, and the underlying stabilizing mechanism was elucidated. The results showed that the microstructure of matrix was spheroidal pearlite after annealing and transformed to martensite after stabilizing heat treatments. The average TiC particle size of annealed cemented carbide was 2.22 μm, which decreased to 2.09 μm after quenching and increased to 2.31 μm and 2.29 μm after tempering and TCC treatments, respectively. In addition, the TiC particles in cemented carbide had obvious fractal characteristics. The ultimate strain of cemented carbide after tempering and TCC treatment was 3.01 × 10−4 and 8.38 × 10−5, and the dimensional stability of the tempered specimen was relatively poor. Therefore, the TCC treatment not only improved the strength of cemented carbide, but also significantly improved the dimensional stability of TiC steel-bonded cemented carbide. A variety of stabilizing mechanisms, including martensitic transformation, retained austenite-martensite transformation, martensite refinement, fine carbides precipitation, and residual stress release affected the microstructure and properties of cemented carbide during the stabilizing heat treatments, hence resulting in a significantly improvement of the dimensional stability of TiC steel-bonded cemented carbide.

Influence of the Inherited Structure Induced by Al and Si Alloying on Microstructure Evolution and Mechanical Properties of 100Cr6 Steels

The fatigue lifetime of high‐strength 100Cr6 steels can be improved by an increased content of retained austenite that can be induced by Al and Si alloying. The related deformation‐induced retention of the austenite–martensite transformation during cyclic loading increases their local strain hardening capacity. However, for those 100Cr6 steels containing retained austenite, sufficient dimensional stability must be ensured. In this study, two standard 100Cr6 steels alloyed either with 1.5 wt% Al or 1.5 wt% Si (to diminish carbide formation and accordingly promote austenite retention) are laboratory melted and processed to adjust a microstructure of bainite, retained austenite, and carbides. The segregation simulation in the as‐cast condition and the corresponding microstructures in the forging and heat‐treating conditions are investigated. The inheritance of chemical heterogeneity leads to structural heterogeneity on both the nano‐ (nm) and micro (μm) scales. This heterogeneity is much more pronounced in the Al‐alloyed steel, which can be attributed to inheritance from the as‐cast state. While the results of the quasistatic tensile tests are comparable for both alloys, the cyclic load increase tests indicate a higher fatigue strength of the Si‐alloyed steel, which can be explained with the more homogenous microstructure and the finer distribution of the retained austenite.