The hot compression experiments were performed to thoroughly explore the effect of the cooling rate on the microstructural characteristics and mechanical properties of hypereutectoid pearlite steel. The results showed that the lamellar spacing of pearlite was refined by 15

High-strength martensitic steels are extensively used in aerospace, automotive manufacturing, marine engineering, and other demanding applications due to their exceptional mechanical properties. In this work, an active learning strategy integrated with a genetic algorithm is proposed to accelerate the efficient design of ultra-high-strength steels (UHSS) with enhanced resistance to hydrogen embrittlement (HE). After three iterative optimization cycles, alloy compositions meeting the targeted performance metrics are successfully identified. Mechanical properties of selected alloys are subsequently validated through hydrogen-charged slow strain rate tensile (SSRT) testing. Concurrently, high-resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT) are employed to elucidate key microstructural features. According to HRTEM statistical results, volume fraction of VC precipitates is about 0.623%, which acts as a hydrogen capture site and can effectively reduce sensitivity to HE. This methodology not only streamlines design process for UHSS and markedly enhances research and development efficiency, but also provides a solid theoretical foundation for performance optimization and practical application of high-strength steels.

Conventional high-Mn steels rely on high Mn content to achieve excellent mechanical properties through the TWIP (twinning induced plasticity) effect; however, the elevated Mn content increases cost and leads to multiple processing challenges (e.g., welding, galvanizing, etc.). Reducing the Mn content to the medium-Mn range tends to shift the deformation mechanism from TWIP to TRIP (transformation induced plasticity) due to the reduced austenite stability and stacking fault energy (SFE), which usually causes quasi-cleavage fracture. In this study, a medium-Mn austenitic steel with 12 wt% Mn was developed, in which coherent disordered nanoprecipitates refined the grain size to 0.9 mu m, thereby increasing the SFE by 7.2-9.9 mJ m-2 and enhanced austenite stability. In addition, the high density of coherent disordered nanoprecipitates effectively refined nanotwins and epsilon-martensite, enabling a transition in deformation mechanisms from coarse epsilon- and alpha '-martensitic transformations to sequential activation of stacking faults (SFs), nanotwinning and nanoscale epsilon-martensitic transformation. As a result, the ultrafine-grained medium-Mn austenitic steel exhibited significantly improved tensile properties, with a yield strength of 578 MPa, an ultimate tensile strength of 1148 MPa and an elongation of 76 %. These findings overcome the limitations in plasticity and work hardening capability caused by low Mn content in medium-/ high-Mn austenitic steels, and provide valuable insights into balancing Mn content and deformation mechanisms of high Mn steels for their widespread application.

To clarify whether fast cooling inhibits Sn grain boundary segregation, an artificially contaminated steel (Sn 0.05 wt.%) was resistance spot welded. The chemical compositions of prior austenite grain boundaries were examined by three-dimensional atom probe. Results show that Sn segregation persisted even under fast cooling via resistance spot welding. The measured segregation level substantially exceeds predictions from equilibrium models, indicating a deviation from classical equilibrium behaviour. Cross-tensile tests of welded joints revealed intergranular fracture along prior austenite grain boundaries, which is direct evidence of the deteriorating effect of Sn grain boundary segregation. This study reveals that fast cooling fails to inhibit Sn grain boundary segregation, and Sn segregation cannot be ignored, especially when employing processing techniques with fast cooling.

Achieving a favorable strength–toughness balance in thick-section low-alloy steels remains a critical challenge for structural applications. The effects of lamellarization annealing (L) and subsequent tempering (T) temperatures on microstructural evolution and mechanical performance were systematically examined in a 30-mm-thick thermo-mechanical controlled processing plate. The L temperature was varied from 800 to 860 °C, followed by T at 400–550 °C. Microstructural evolution was characterized using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and X-ray diffraction (XRD), while tensile and Charpy V-notch impact tests were conducted to evaluate mechanical performance. Lower L temperatures (800 and 820 °C) promoted the formation of heterogeneous lamellar structures composed of martensite/bainite and intercritical ferrite. This microstructural heterogeneity enhanced plastic deformation capability and low-temperature impact toughness by increasing the density of high-angle grain boundaries and promoting favorable dislocation configurations. In contrast, higher L temperatures (840 and 860 °C) led to microstructural homogenization and dislocation accumulation, which improved strength but significantly deteriorated toughness. T at 400 °C resulted in insufficient recovery and limited toughness improvement. An optimal strength–toughness balance was achieved at 500 °C, whereas T at 550 °C caused over-recovery, leading to a slight reduction in toughness despite enhanced ductility. XRD analysis revealed that a high fraction of screw dislocations combined with a moderate dislocation density enhanced crack-tip plasticity and ductile fracture behavior. The L810T500 condition (810 °C represents an intermediate L temperature within the optimal range of 800–820 °C) achieved the best synergy: tensile strength 900 MPa, elongation of more than 17

Zn-coated hot-stamping steels are attractive for corrosion-resistant, lightweight automotive structures, but their application is limited by liquid metal embrittlement (LME) caused by liquid Zn penetration during hot stamping. In this study, coating microstructure evolution and associated LME behaviour were systematically investigated. This was achieved by directly comparing short-process hot-rolled galvanizing with conventional cold-rolled continuous-annealing galvanizing on compositionally matched steels. The short-process route produced an oxide-lean substrate surface with a denser inhibition layer, whereas the conventional route generated pronounced selective oxidation of Mn, Si, and Cr at the coating/substrate interface. During austenitization at 900 °C, the oxide-lean interface promoted Fe dissolution and FeZn interdiffusion, producing a thicker and more uniform alloy layer after hot stamping (31.8 ± 2.6 μm for the HR-coated sample versus 21.1 ± 1.8 μm for the CR-coated sample) which was rich in α-Fe(Zn) and Γ-Fe3Zn10. By contrast, the oxide-contaminated interface in the CR-coated sample delayed the alloying reaction and prolonged the presence of liquid Zn during austenitization. During stamping, this residual Zn penetrated grain boundaries and subsequently transformed into a Zn-rich FeZn phase upon cooling, producing a crack-path Zn signal more than twice that of the HR-coated sample. These findings show that process-route-induced interfacial conditions strongly affect FeZn alloying kinetics and the extent of Zn penetration along crack paths. By creating an oxide-lean interface, hot-dip galvanizing of short-process hot-rolled substrates accelerates alloying and limits residual liquid Zn, providing a practical processing strategy for developing corrosion-resistant galvanized advanced high-strength steels with reduced LME susceptibility during hot stamping.

A heat treatment regime integrating solution treatment, deep cryogenic treatment and double aging was applied to commercial 17-4 PH martensitic stainless steel to achieve synergistic optimization of mechanical properties through precise microstructural control. The effectiveness of this double aging strategy lies in its tailored microstructural evolution: the initial low-temperature aging step promotes a B2-*BCC-*9R structural transition in Cu-rich precipitates while ensuring their fine and uniform distribution. The subsequent short-term hightemperature aging step leads to no structural transformation of Cu-rich precipitates, which only undergo slight coarsening, while effectively facilitating the formation of a significant fraction of film-like reversed austenite with superior thermodynamic and mechanical stability. Distributed along martensite lath boundaries, this filmlike austenite continuously provides the transformation-induced plasticity (TRIP) effect during deformation, effectively deflecting crack propagation paths and accommodating greater plastic deformation, thereby serving as the key contributor to toughness enhancement. Quantitative analysis of strengthening mechanisms reveals that dislocation strengthening and precipitation strengthening are the dominant contributors to the overall yield strength. This double aging approach successfully achieves simultaneous and substantial improvements in strength, ductility, and toughness, with yield strength reaching 1080 MPa, total elongation of 17.2%, and roomtemperature impact toughness exceeding 240 J/cm2.

Castrip employs continuous casting strips typically under 2 mm in thickness, representing near-net-shape manufacturing technology. However, its inherent process constraints, including low-temperature rolling and single-pass reduction, collectively inhibit dynamic recrystallization, yielding coarse prior austenite grain size of about 386 μm. Therefore, refining the transformed microstructures during medium-/high-temperature coiling under such constraints presents a critical challenge. A novel approach leveraging solute-segregated chemical interfaces as the nucleation sites to trigger the intragranular ferrite transformation was introduced for industrial Castrip low-alloyed high-strength steel. The solute-segregated chemical gradients (0.85–4.0 wt.

A new 1300 MPa ultrahigh-strength strip casting steel with high ductility was developed in this work. The effects of silicon (Si) content on the microstructure, mechanical properties, and deformation mechanisms of the steels were investigated and discussed in detail. Our results suggest that Si can effectively retard bainitic transformation kinetics, thereby inhibiting the coarsening of the bainite laths and contributing to the increase in retained austenite (RA) volume fraction. Meanwhile, the precipitation of cementite is markedly suppressed with increasing Si content, which renders more carbon partitioned into the untransformed austenite during the bainitic transformation, thereby further increasing the volume fraction and stability of RA. Mechanical tests indicate that increasing the Si content from 0.5 wt% to 1.5 wt% significantly improves yield strength and tensile strength from 919 MPa and 1104 MPa to 1055 MPa and 1331 MPa, while the ductility rises from 12.2% to 17.8%. This can be attributed to the refined bainitic microstructure, which markedly enhances the strength and provides a greater capacity for dislocation multiplication and storage, thereby contributing to the enhanced work-hardening capability and ductility. Meanwhile, the higher volume fraction and enhanced stability of RA in the high Si steels also favors sustained high work-hardening capacity via sequential activations of stacking faults, nanotwinning, and epsilon-martensite transformation with increasing strain. These findings provide valuable insights into the design of high-performance strip casting steels.

The warm compression behavior and microstructural evolution of GCr15 bearing steel were investigated by single-pass isothermal compression at 650-720°C and strain rates of 0.01-10 s−1. The flow curves showed strong temperature and strain-rate dependence: at 10 s−1, the peak stress decreased from 370 MPa at 650°C to 293 MPa at 720°C, reflecting enhanced thermally activated softening. A peak-stress-based Arrhenius constitutive model was established with an apparent activation energy of 278.17 kJ mol−1 and a stress exponent of 6.34. The model accuracy was evaluated using AARE and RMSE, giving 7.53% and 18.13 MPa, respectively. A strain-compensated constitutive model was further developed by introducing strain-dependent material constants. Processing maps constructed at true strains of 0.1, 0.5, and 0.9 showed that the stable high-efficiency domain gradually evolved toward the intermediate-temperature and low-strain-rate region. SEM, EBSD, carbide morphology statistics, and hardness measurements revealed that low-temperature/high-strain-rate deformation produced elongated deformation bands, high local misorientation, and incomplete carbide spheroidization, whereas low-strain-rate deformation promoted dynamic recovery, recrystallization-like low-strain regions, and carbide spheroidization. The 680°C/0.01 s−1 condition exhibited the highest spheroidization index and a relatively low aspect ratio while maintaining moderate hardness. Although 720°C/0.01 s−1 showed the highest GOS <2° area fraction, it caused carbide coarsening and significant hardness reduction. Unlike previous studies focusing mainly on constitutive behavior or microstructural observation alone, this work directly correlates strain-dependent constitutive response, processing-map stability, carbide spheroidization, EBSD-derived GOS/KAM indicators, and hardness. The optimum warm-compression window was identified as 665-685°C and 0.01-0.02 s−1.

This study bridges the macroscopic thermomechanical response and microscopic phase transformation kinetics of a low-carbon gear steel during hot deformation across a wide temperature range (650-1000 °C). By developing a friction-corrected constitutive model and processing maps, the macroscopic flow instability and power dissipation mechanisms were systematically delineated, identifying an optimal dynamic recrystallization (DRX) window at 800-950 °C. The hot deformation activation energy was determined to be 374.3 kJ/mol. Beyond the conventional high-temperature DRX, we explicitly reveal the complex multiphase evolution during warm deformation in the two-phase region. In this regime, the stored defect energy within the unrecrystallized austenite strongly triggers the deformation-induced ferrite transformation (DIFT), the abnormal kinetics of which are elucidated through the competition between early nucleation site saturation and carbon diffusion-controlled growth. Furthermore, crystallographic reconstruction uncovers that the parent austenite, DIFT ferrite, and subsequent martensite strictly conform to the Kurdjumov-Sachs (K–S) orientation relationship. This specific interfacial conformity strategically minimizes interfacial energy, fundamentally facilitating the rapid phase transitions observed during deformation. These findings provide practical guidance for microstructure control in low-carbon gear steel by clarifying that deformation in the fully austenitic region favors prior-austenite refinement through dynamic recrystallization, whereas warm deformation in the two-phase region enables the tailoring of ferrite/martensite dual-phase microstructures through deformation-induced ferrite transformation.

The oxidation behavior of press hardening steel (PHS) during hot forming significantly influences dimensional accuracy of the final component. While co-alloying with high concentrations of Cr and Si effectively enhances oxidation resistance, it considerably increases material costs due to the expense of chromium. In this study, we propose a cost-effective alternative by employing individual Si alloying to address the oxidation resistance challenge in PHS. The high-temperature oxidation behaviors of Fe-0.2C-1.0Mn-xSi alloys (x = 0%, 0.5%, 1.5 wt %, simplified as 0Si, 0.5Si and 1.5Si) was systematically investigated in the 880-950 degrees C range. The results show that 1.5Si sample exhibits the optimal oxidation resistance, comparable to that of high-cost Cr-alloyed sample. This performance is attributed to the formation of a continuous Si-rich oxide layer at the iron oxide scale/matrix interface. In addition, unique Mn-rich oxides present at the gaps of iron oxide scales on the 1.5Si sample, which enhances the compactness and resistance to spallation. These Mn-rich oxides grow by consuming the (Mnx, Fe2-x) O3 oxides within the Si-rich oxide scale, leading to the absence of Mn-rich oxides in the iron oxide scales of the low-Si samples. The synergistic protective effect of Si-rich oxide scale and Mn-rich oxides occurs in the high-Si sample, effectively inhibiting diffusion of oxygen anions or metal cations, significantly improving the oxidation resistance. Our work not only presents a cost-effective alloy design for PHS, but also elucidates a novel synergistic mechanism for enhancing oxidation resistance.

The utilization of recycled steel is essential for achieving carbon neutrality and sustainable engineering, yet repeated recycling inevitably leads to the accumulation of residual elements that are difficult to remove during conventional refining. Among them, copper (Cu) readily enriches in scrap-based steels and is a primary cause of surface hot shortness during high-temperature processing due to its segregation at the oxide/steel interface. While the compositional effects of Cu have been extensively studied, the influence of thermo-history associated with different industrial processing routes remains poorly understood. In this work, Cu enrichment during high-temperature oxidation was systematically investigated under thermo-histories representative of conventional hot rolling, thin slab continuous casting and rolling (TSCR), and strip casting. Plain carbon steels containing 0.05-0.30 wt.% Cu were oxidized at 1000-1200 °C, and interfacial microstructures were characterized using SEM-EDS. The results show that Cu enrichment is highly sensitive to both temperature and thermal exposure time, with a critical temperature range of 1100-1150 °C promoting the formation of continuous Cu-rich liquid films. Prolonged thermo-history in conventional hot rolling markedly enhances Cu enrichment, TSCR partially suppresses interfacial segregation, whereas strip casting effectively inhibits Cu enrichment even at elevated Cu contents. These findings highlight thermo-history as a dominant factor controlling Cu-induced surface hot shortness and provide guidance for process optimization in recycled steels.

To address the high-salinity and hyper-humid thermal environment of tropical oceans and meet industrial demands for high strength and lightweight, austenitic low-density steel was developed as a novel corrosion-resistant steel. A 3.5 wt.% NaCl solution was used to simulate the marine environment to study the effect of Si on the corrosion behavior of this steel. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and electron probe microanalysis (EPMA) were employed to characterize the microstructures and corrosion behaviors of two test steels, as well as the phase compositions and element distributions of corrosion products after polarization and cyclic immersion accelerated corrosion tests. The results show that a dense oxide film initially forms on the steel surface in 3.5 wt.% NaCl solution at the early corrosion stage. Si addition induces SiO2 formation and promotes Al conversion to Al2O3, enhancing oxide film compactness and inhibiting matrix atom outward diffusion and Cl- inward penetration. With prolonged corrosion, the oxide film is dissolved or broken, forming a dense rust layer dominated by Fe3O4, Fe2O3 and FeOOH. Si enriches in the inner rust layer adjacent to the matrix and pitting cavities, inhibiting pitting deepening and promoting γ-FeOOH to α-FeOOH transformation, thus improving the steel's corrosion resistance.

The segregation of tin (Sn) at prior austenite grain boundaries (PAGBs) in steel significantly deteriorates the hot workability and mechanical properties. However, the segregation mechanisms of Sn during thermomechanical processing are still unclear. In this study, atom probe tomography (APT) analysis of the compositions of PAGBs in martensitic steels suggests that the extent of Sn enrichment at PAGBs is closely related to thermomechanical processing conditions. Thermal deformation in the non-recrystallization region introduces a high density of dislocations, which kinetically facilitates Sn segregation at PAGBs. By contrast, no significant Sn enrichment at PAGBs is observed in recrystallized conditions, which is attributed to the rapid annihilation of dislocations. These findings provide valuable insights into the design of thermomechanical processing conditions for steels that contain elements having strong segregation tendencies, e.g., Sn, As, Sb, etc.

Driven by efforts toward carbon-neutral steelmaking, increased scrap usage elevates Sn content in steels. While the general effects of Sn on steel have been studied, its specific influence on resistance spot welding (RSW) remains unclear. This study investigates Sn’s impact on the mechanical properties of RSW joint of 460 MPa HSLA steel. Cross-tension tests reveal that both the RSW joint without Sn and the RSW joint·containing 0.09wt

The steel industry’s shift towards scrap-based, low-carbon steelmaking introduces residual Sn, which compromises the resistance spot weldability of advanced hot-stamping steels essential for automotive lightweighting. This study investigates the impact of Sn on the mechanical properties of such welds and evaluates a shim-assisted RSW (SA-RSW) process using an interstitial-free steel shim for mitigation. Increasing Sn content degraded the cross-tension performance, with a critical content of 0.05% causing a transition from the desirable pull-out fracture to partial interface fracture and a 20% reduction in peak load, primarily due to Sn segregation. The SA-RSW process effectively diluted Sn concentration in the fusion zone by ∼66%, restoring the pull-out fracture mode. However, it concentrated residual stress near the fusion line, leading to cleavage brittle fracture and reduced displacement, which diminished energy absorption despite Sn-induced strengthening increasing the peak load. Based on these results, a practical selection strategy is proposed. Using conventional RSW for Sn content below 0.05%, and adopting the SA-RSW process for Sn content at or above 0.05%. This work provides insights into Sn-induced embrittlement and a viable joining strategy for sustainable manufacturing

To alleviate the pronounced strength degradation of axle housing steels after hot stamping, a newly designed 500 MPa grade V-N microalloyed steel was developed. The individual and synergistic effects of vanadium and nitrogen contents on the microstructure evolution and mechanical properties, both before and after hot stamping, were systematically investigated via optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results demonstrate that V-N microalloying fundamentally alters the phase transformation behavior compared to a plain C-Mn steel. Increasing V and N contents remarkably improved the yield strength (YS) and tensile strength (TS) of both hot-rolled plates and hot-stamped components. However, the hot stamping process led to a substantial strength loss, whose magnitude correlated positively with the V and N levels. While the plain C-Mn steel exhibited the lowest strength loss rate, its initial hot-rolled strength was insufficient, resulting in poor final performance. An optimal combination of high initial strength and acceptable post-stamping strength retention was identified in the steel with 0.05% V and 0.02% N (V5N20), exhibiting post-stamping properties of YS = 420 MPa, TS = 548 MPa, and elongation = 36.0%. Nitrogen was found to be more influential than vanadium, primarily because pre-existing V(C,N) precipitates effectively inhibited austenite grain coarsening during reheating and promoted intragranular ferrite nucleation during cooling. The partial dissolution and subsequent reprecipitation of these particles during the stamping cycle enhanced both grain refinement and precipitation strengthening, thereby offering an effective strategy to mitigate the strength degradation inherent to the hot stamping process.

Hydrogen embrittlement (HE) continues to be a major challenge in high-strength steels, particularly due to hydrogen-induced interfacial decohesion mechanisms. This study investigates the previously unexplored effects of trace tramp elements on HE resistance of quenching and partitioning (Q&P) steels. Our previous research demonstrated that minor additions of trace tramp elements (As, Sn and Sb) refined the microstructure and improve the strength-ductility synergy of a Q&P steel. Nevertheless, in this work, hydrogen-charged slow strain rate tensile tests show that the Q&P steel containing these trace tramp elements (QP-R) exhibits substantially increased HE susceptibility (78.5%) compared to its counterpart without the tramp elements (QP) (28.2%). Density Functional Theory (DFT) calculations reveal a synergistic effect between hydrogen and individual tramp element (As, Sn, or Sb), which substantially weakens the Fe-Fe interatomic bonding at the grain boundary and reduces the interfacial cohesive strength. Fractographic and crack-path analyses further distinguish the operative mechanisms, showing the hydrogen-enhanced decohesion (HEDE) mechanism in the QP-R steel vs. the hydrogen-enhanced localized plasticity (HELP) mechanism in the QP steel. Notably, the detrimental effects of these trace tramp elements on the HE mechanism in the QP-R steel occur without detectable grain boundary segregation, suggesting that local electronic interactions among dilute tramp-element atoms, hydrogen, and iron are suffice to weaken grain boundary cohesion. These findings highlight an often-overlooked compositional sensitivity of high-strength steels to the trace tramp elements and emphasize the necessity for manipulating the distribution of the trace tramp elements to mitigate HE in high-strength steels.