Search Results (3,039)

In this work, the effect of partial to complete Al substitution of Si on the microstructure, retained austenite (RA) stability, and mechanical properties of cold-rolled TRIP-aided steels was investigated. Four experimental TRIP-aided steels (Fe-0.2C-1.5Mn-1.5/1.0/0.5/0Si-0/0.5/1.0/1.5Al-0.025Nb, wt.%) were designed. The results indicate that replacing Si with Al significantly increases the volume fraction of soft polygonal ferrite (from 52% to 73%) and decreases that of bainite. Although the volume fraction of RA decreases (from 15.6% to 12.4%), its average carbon content and, consequently, its mechanical stability are enhanced, which suppresses the strain-induced martensitic transformation. In terms of mechanical properties, the substitution leads to a monotonic decrease in both yield strength (from 573 MPa to 536 MPa) and ultimate tensile strength (UTS) (from 839 MPa to 648 MPa), primarily due to reduced solid-solution strengthening, coarsened ferrite grains, and a weakened TRIP effect. Conversely, the total elongation (TEL) increases from 28.3% to 32.4%, attributed to the higher fraction of ductile ferrite. Consequently, the product of tensile strength and total elongation (PSE) exhibits a slight decline. The 1.5Si-TRIP steel exhibited the most balanced mechanical properties, achieving the highest PSE of 23.7 GPa·%. Full article

By adding Ce to high-strength low-alloy steel, the effects of heating parameters and Ce on grain growth were examined through in situ observation and dynamic analysis of grain growth behavior during heating, combined with precipitated phase analysis and pinning force calculations. In situ observation of the heating process revealed the behavior of grain growth and grain boundary migration in real time, providing an intuitive and accurate illustration of the effect of Ce on grain growth behavior. The mechanism of Ce’s role in refining austenite grains was clarified. The results revealed that at 1050 °C, Ce had little effect on grain growth. Ce delayed the grain coarsening temperature from 1050–1150 °C to 1150–1250 °C, resulting in grain refinement. The predicted results from the established dynamic model were consistent with the grain growth process, demonstrating high predictive accuracy. After Ce treatment, the activation energy for grain growth increased from 172.058 to 193.703 kJ/mol, representing a 12.58% rise, rendering grain growth more difficult. Within the holding temperature range, small spherical Nb-rich (Nb, Ti)(C, N) and large rectangular Ti-rich (Nb, Ti)(C, N) existed. The addition of 0.0070% Ce delayed the dissolution of Nb-rich carbonitrides. Finer precipitated phases and high-melting-point, fine Ce₂O₂S and CeAlO₃ inclusions at grain boundaries provided greater pinning force, inhibiting grain growth. Full article

A microalloyed high-carbon low-alloy steel was designed to clarify the combined effects of austenitizing temperature and deep cryogenic treatment (DCT) on microstructural evolution and mechanical performance. Specimens were austenitized at 770–900 °C, water-quenched, subjected to DCT at −196 °C, and subsequently tempered at 180 °C. Microstructural characterization by XRD, EBSD, and TEM indicates that the quenched microstructure is dominated by martensite and cementite, with retained austenite below 1% at moderate austenitizing temperatures. DCT does not fundamentally alter the martensitic morphology but promotes the transformation of retained austenite and induces substructure fragmentation, dislocation reorganization, and a more homogeneous lattice strain distribution. Concurrently, carbon redistribution during cryogenic exposure facilitates the formation of finely dispersed carbides. After tempering, partial recovery and stabilization of the martensitic substructure lead to reduced lattice distortion while maintaining a high density of effective strengthening features. Mechanical testing shows that DCT combined with appropriate austenitizing (770–790 °C) improves hardness and ultimate tensile strength with acceptable ductility, whereas excessive austenitizing at 900 °C results in severe grain coarsening and intergranular brittle fracture. The results demonstrate that optimized integration of microalloying and DCT enables a favorable strength–toughness balance in high-carbon tool steels. Full article

The current study explored the martensite structures of Fe₃Pt alloys, specifically $Cmmm$-Fe₃Pt, $P{6}_3/mmc$-Fe₃Pt, $P4/mmm$-Fe₃Pt, and $R\overline{3}m$-Fe₃Pt, aiming to provide a comprehensive understanding of the mechanisms that govern their physical and chemical properties. We have focused on their structural, thermodynamical, magnetic, electronic, mechanical, and dynamical characteristics, utilizing the density functional theory (DFT) technique. Our study revealed that in addition to the previously reported austenitic cubic $Pm\overline{3}m$-Fe₃Pt and martensite tetragonal $I4/mmm$-Fe₃Pt with L1₂ structure, there exist additional Fe₃Pt phases that exhibit excellent structural, thermodynamic, magnetic, and mechanical properties. The calculated enthalpies of formation were found to be negative and less than −0.39 eV in all the structures considered, indicating thermodynamic stability and formation under experimental synthetic conditions. Moreover, the computed magnetic moments are in the range 2.94 to 3.04 ${\mathsf{\mu }}_{\mathrm{B}}$, which is relatively comparable to 3.24 ${\mathsf{\mu }}_{\mathrm{B}}$ of the widely reported $Pm\overline{3}m$-Fe₃Pt alloy. The analysis of the electronic structure also revealed strong magnetism due to the presence of asymmetry in the spin-up and -down states of the density of states (DOS) plots. To determine the mechanical response of Fe₃Pt structures under loading conditions, we computed the independent elastic constants, macroscopic properties, and stress–strain relationship under hydrostatic stress. All four phases were studied, but the hypothetical $P{6}_3/mmc$-Fe₃Pt showed excellent mechanical stability at ambient conditions and exceptional hardness and resistance to compression in the elastic region 0% ≤ strain ≤ 10%. This evidence is provided by satisfying the Born necessary stability conditions, large bulk modulus, and a strong linear relationship fit ($R^2$) of greater than 0.94. Moreover, the phonon dispersion curves revealed dynamical stability for $Cmmm$-Fe₃Pt and $R\overline{3}m$-Fe₃Pt, and metastability for $P4/mmm$-Fe₃Pt, while the hypothetical $P{6}_3/mmc$-Fe₃Pt is unstable. Full article

This study investigates the effect of microstructure on water-induced embrittlement of dual-phase austempered ductile iron (ADI). Dual-phase ADI materials were produced by austenitization at 780, 800, 820, and 840 °C followed by austempering at 400 °C/1 h, resulting in microstructures composed of varying fractions of free ferrite and ausferrite. Tensile properties were evaluated under dry conditions and in distilled water. The embrittlement zones were observed in all samples investigated; however, they were not critical in all cases. The results indicate that free ferrite is less sensitive to water-induced embrittlement, whereas increasing ausferrite content promotes the formation and growth of the embrittlement zone. Elongation was identified as the most sensitive mechanical parameter, showing statistically significant reductions of up to ~80% for microstructures containing more than ~65% ausferrite, while proof strength remained largely unaffected. Fracture surface analysis revealed fatigue-like striation features within the embrittlement zone, indicating cyclic crack initiation and propagation. Based on correlations between tensile behavior, fracture morphology, and microstructural features, a water-induced embrittlement mechanism involving cyclic local chemisorption and surface-initiated crack growth is proposed. These findings highlight the critical roles of phase type, volume fraction, and spatial distribution in controlling the resistance of dual-phase ADI to embrittlement in aqueous environments. Full article

High nitrogen austenitic stainless steels are an important engineering structural material. Under annealing conditions, the addition of interstitial solid solution element nitrogen can improve the yield strength and tensile strength of the alloy without reducing its plasticity. In addition, nitrogen can partly or completely replace the more expensive nickel element at a relatively cheap element cost to improve economic benefits, while maintaining or even enhancing the excellent corrosion resistance of stainless steels. However, the cracks and defects caused by high nitrogen austenitic stainless steels during hot working in high temperature ranges have always been the pain points in the engineering field. High nitrogen elements bring high temperature strength, but also narrow the hot working temperature range, the possibility of nitride precipitation and the tendency of heat induced cracking, which limit the further engineering application of high nitrogen austenitic stainless steels. It is urgent to analyze and study the hot deformation law of high nitrogen austenitic stainless steels in engineering. This article commences with an examination of the developmental trajectory of high nitrogen austenitic stainless steel, elucidates the role and strengthening mechanism of nitrogen, and delineates the factors influencing the mechanical behavior of high nitrogen austenitic stainless steel during hot working. These factors include the impact of nitrogen content and manufacturing processes, hot-working parameters, grain size distribution, and the presence of precipitated phases. This article synthesizes various studies, analyzes the causes of thermal cracking, and proposes potential solutions. Ultimately, it summarizes the practical applications and future prospects of high nitrogen austenitic stainless steel, highlighting its substantial potential. Full article

Analyses of the oxidation characteristics of HR3C austenitic steel exposed to supercritical carbon dioxide were carried out at temperatures ranging from 600 to 650 °C under 25 MPa. It was observed that the weight gain increased with increases in temperature and time. The oxide morphology and phase were characterized using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Furthermore, the three-dimensional morphology and chemical composition of the surface oxide were inspected using a secondary ion mass spectrometer (SIMS). The majority of the oxide formed on HR3C at 600–650 °C was Cr₂O₃. Carbon enrichment occurs on the surface of the oxide scale and the oxide–substrate interface due to a carbonization reaction. The corrosion mechanism is also discussed in this paper. Full article

Decarburization during austenitization degrades the surface integrity and mechanical performance of tool steels, yet the quantitative influence of process pressure remains unclear. In this study, the effect of process pressure on the decarburization behavior of H13 tool steel was investigated. Specimens were austenitized at 920–1020 °C for 60 min under pressures ranging from 0.01 to 760 Torr. Carbon concentration profiles were measured by electron probe microanalysis, and hardness degradation and mass loss were evaluated. A one-dimensional diffusion model with a Robin boundary condition was applied to describe the coupled effects of carbon diffusion and surface reaction. High-vacuum conditions suppressed decarburization, whereas increasing pressure accelerated carbon loss, leading to deeper decarburized layers and pronounced hardness reduction. The model reproduced the experimental results and revealed a pressure-dependent transition in the dominant decarburization mechanism. Full article

The relaxation calorimeter option in the commercial Physical Property Measurement System (PPMS) has become widely used. Since its introduction, the capabilities of this technique for specific heat measurements have been critically discussed, particularly to avoid misinterpretation of data near phase transitions. Traditional methods rely on cooling curves after sample excitation, where sharp latent heat contributions during heating lead to clear deviations from the fitting model. However, subtle but extended enthalpy contributions (e.g., strain release) may mask these effects, allowing both heating and cooling curves to be well fitted using the standard PPMS protocol. In this work, we develop a procedure that assumes a constant extra power supplied due to subtle enthalpy contributions, enabling consistent interpretation of both heating and cooling curves. This procedure allows: (1) correction of specific heat measurements; and (2) quantification of the enthalpy involved in the transition. The procedure is applied to a magnetic-field-induced transformation in MnCo(Fe)Ge(Si) alloys. Two samples were studied: a single-phase austenite without any field-induced transition, used as a reference, and a mixed austenite-martensite sample, in which apparent deviations in the conductance of the wires evidence the presence of the anomaly. Full article

High-temperature carburization (HTC, 950–1050 °C) has emerged as a pivotal low-carbon, energy-efficient manufacturing technology for gear steels, accelerating carbon diffusion for reducing processing cycles by over 60% while achieving significant energy savings and emission reductions. However, the inherent contradiction between HTC efficiency and microstructural stability, specifically austenite grain coarsening, severely degrades mechanical properties (e.g., strength, toughness, fatigue resistance) and limits widespread application. This review systematically synthesizes recent advances in austenite grain size regulation during HTC of gear steels, focusing on the core scientific framework of “grain coarsening mechanism—regulation strategy—performance enhancement”. It elaborates on thermodynamic and kinetic mechanisms of austenite grain growth, ripening behavior of microalloying precipitates (Nb(C,N), Ti(C,N), AlN, etc.), and their synergistic grain-refining effects. Comprehensive coverage of regulatory strategies (microalloying design, pretreatment technologies, process optimization, and integrated regulation) and characterization techniques is provided, along with a quantitative correlation between grain size, microstructure, and surface performance (wear resistance, corrosion resistance, and fatigue life). Numerical simulation and predictive models (empirical, theoretical, multiphysics coupling, machine learning-based) are critically analyzed, and current challenges (temperature-grain stability trade-off, multifactor synergy understanding, industrial scalability) and future research directions (advanced microalloying systems, intelligent process optimization, cross-scale modeling, green technology integration) are proposed. This review aims to provide theoretical guidance and technical support for optimizing the HTC performance of gear steels, catering to the demands of high-power-density transmission systems in automotive, aerospace, and heavy machinery industries. Full article

In this study, hardfacing and a flux-cored/self-shielded powder wire of the FCAW-S-90G13N4 type was employed to produce and investigate the deposits of high-manganese steel. The effects of high-frequency mechanical impact (HFMI) treatment on the microstructure, hardening, and scratch resistance of the deposits were studied to evaluate and predict the impact wear resistance of the hardfacing deposits under controlled impact load conditions. As observed by XRD, SEM, and nanoindentation, the microstructure of deposited metal comprised a soft austenite matrix, dispersed hard carbides, and an ε phase (~26 vol.%). The wear resistance is thus not controlled by carbides alone but arises from the synergistic action of a hard carbide network within a ductile matrix. HFMI resulted in twinning, an increase in dislocation density, a grown volume fraction of ε (>60%) and α′-martensite. The interaction between twins, martensites, and dislocations provides a double/triple increase in microhardness (from HV_0.2 = 2.78 GPa to HV_0.2 = 6–7.69 GPa). After HFMI, scratch tests showed lower restored depths of scratch tracks and a 36–68% deceleration in the wear rate regarding those of the initial deposit. The underlying wear mechanisms were assessed accounting for the SEM observations of the scratch track morphologies and a ‘counterbody penetration vs. shear stresses ratio’ map. The initial plastic deformation-related mechanism (wedge/pile-up formation) changed by HFMI to ploughing. The obtained results allow one to evaluate and predict the impact wear resistance of the hardfacing deposits under controlled impact load conditions. Full article

The objective of this article is to optimise the deposition modes and the content of exothermic additions (EAs) in the core filler in Fe-C-Cr-Ti with Cu additions hardfacing. To achieve this, JMatPro Release 7.0, Sente Software Ltd., 2016 material characterisation software was used to simulate and calculate the equilibrium phase structure and composition of the Fe-C-Cr-Ti-Cu alloy during the welding thermal cycle. A synergistic approach combining the Taguchi–Analysis of Variance (ANOVA)–Factorial design (FD) method with the standard hybrid Taguchi–ANOVA–Principal Component Analysis (PCA)–Grey Relational Analysis (GRA) is used and justified to optimise factors and develop mathematical models for parameters in the L9 orthogonal experimental design. The study examines how the transfers of deoxidisers depend on the content of exothermic additions in the cored wire filler (EA) and the contact tip-to-work distance (CTWD), while the behaviour of carbide formers is influenced by wire feed speed (WFS) and present arc voltage at the power source (U_set). The research specifically investigates the Fe-C-Cr-Ti-Cu system and the role of copper in stabilising austenite. Findings show that high Cu concentrations (7 wt.%) enhance hardenability by 13%, effectively suppressing pearlite transformation and expanding the bainite region. The desired chemical composition of the deposited metal is determined by the distribution of selected factors, as measured by the transfer coefficients of each element. Full article

This study systematically investigates the effect of trace Ti addition on the impact toughness and underlying deformation mechanisms of high-Mn austenitic steel from 298 K to 4.2 K through instrumented Charpy impact testing, dynamic J-R curve analysis, and multi-scale microstructural characterization (SEM, TEM). The results show that Ti addition leads to the formation of Ti(C,N) precipitations, which act as microcrack initiation sites and significantly reduce the impact-absorbed energy at room temperature (298 K) from 249 J to 189 J. However, as the temperature decreases to liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures, the impact toughness of the Ti-added steel does not deteriorate further and remains comparable to that of the Base steel. This temperature-dependent behavior originates from a transition in the dominant deformation mode. At room and moderately low temperatures, deformation is primarily governed by dislocation slip, whose strong interaction with coarse precipitates leads to premature cracking. At cryogenic temperatures, the significantly reduced stacking fault energy (SFE) shifts the deformation mechanism to the predominant formation of high-density nano-twins. These dense deformation twins enhance the matrix via the dynamic Hall–Petch effect and mitigate the detrimental effect of precipitates by alleviating interactions between dislocations and precipitates. Full article

To solve the copper brittleness problem of copper-bearing steel, support the ferritic rolling process, and ensure the continuity of rolling across different phase regions, this study focused on copper-bearing steel with w(Cu) = 1.56%. Gleeble thermal simulation tests were conducted to investigate the deformation behavior of Cu-bearing steel, and a corresponding deformation resistance model was established; meanwhile, the precipitation characteristics of the second phase were characterized by high-resolution transmission electron microscopy (HRTEM). The results show that the deformation resistance of copper-bearing steel increases with decreasing temperature and increasing strain rate, and its deformation resistance–temperature curve shows a unique bimodal trend, where the inflection point at 840 °C is attributed to the austenite–ferrite phase transformation, and the inflection point at 920 °C is caused by the precipitation of B2-FeCu ordered nanoclusters. HRTEM observations confirm that these nanoclusters are metastable phases with a size of less than 5 nm, and their orientation relationship with the matrix is (011)_B2//(011)_α-Fe and [001]_B2//[001]_α-Fe. The area fraction of B2-FeCu ordered nano-precipitates is in the range of 4.27% to 5.32%, which can reduce the lattice distortion of the matrix and thus decrease dislocation slip resistance. The segmented modified Zhou-Guan model has a coefficient of determination (R²) greater than 0.96 between the predicted and experimental values, which can accurately guide the optimization of low-temperature rolling process parameters for copper-bearing steel. Full article

Developing stable alumina-based scales is critical for alumina-forming austenitic (AFA) alloys exposed to highly basic molten carbonates. However, the inherently sluggish diffusion of Al in austenite often limits the establishment of continuous protective layers. Herein, a thermomechanical treatment (TMT) strategy is proposed to enhance short-circuit diffusion pathways and promote selective Al oxidation in a Li–Na–K carbonate melt at 700 °C. After 90% cold rolling, annealing at 800 °C and 1000 °C generated two distinct microstructural states characterized by different grain boundary types, dislocation densities, and NiAl precipitate populations. The 800 °C-annealed alloy exhibits a significantly lower steady-state corrosion rate (~62 μm/yr) compared with the coarse-grained 1000 °C counterpart. EBSD and TEM analyses reveal that ultrafine grains, abundant low-angle boundaries, and finely dispersed NiAl precipitates provide efficient fast-diffusion channels and local Al reservoirs, enabling rapid formation of a continuous LiAlO₂/Al₂O₃ inner layer. In contrast, insufficient Al flux in the 1000 °C microstructure results in extensive internal oxidation and growth of a thick, non-protective LiFeO₂/NiO scale. These findings demonstrate that controlling the defect and grain-boundary structure via TMT is an effective route to overcome Al diffusion limitations and improve the molten-carbonate corrosion resistance of AFA alloys. Full article