Third-generation Advanced High-strength Steels Research Articles

Realization of strength-ductility balance of 10 Mn-steel by tailoring symbiosis microstructure

Medium Mn steel is considered as a third-generation advanced high-strength steel. However, the bottle-neck problems of excessive strength and insufficient plasticity seriously limited its development. In this study, a warm rolling process was employed to refine grains and acquire high-density dislocations. Subsequently, a quenching-tempering process was employed to prepare a symbiosis microstructure containing multi-phase structures and double precipitates (κ- and V-carbides). On the premise of providing a gigapascal-level yield strength, the introduction of multi-phase structures activated various deformation mechanisms during the straining and contributed to a tensile strength of 1777 MPa and total elongation of 14.1 % in sample W500. In sample W700, the high-density dislocations in martensite gradually passed through the austenite/martensite interfaces and entered the neighboring austenite, enhancing the coordinated deformation capacity of martensite. Sample W700 exhibited a total elongation of 21.8 % and tensile strength of 1468 MPa. Combined with a microstructure analysis during the interrupted tensile deformation, the influences of martensite transformation, dislocation motion, double precipitates, and deformation twins on the work hardening and ductility are discussed in detail.

Crystal Plasticity Finite Element Modeling of the Influences of Ultrafine-Grained Austenite on the Mechanical Response of a Medium-Mn Steel

Medium manganese (medium-Mn) steel, one of the third-generation advanced high-strength steels (AHSS), delivers impressive mechanical properties such as high yield strength, ultimate tensile strength, and uniform elongation. One notable feature of medium-Mn steels is the presence of ultrafine-grained (UFG) austenite, achieved through phase transformation from the parent martensite phase during intercritical annealing. While, in general, UFG is considered a strengthening mechanism, the impact of UFG austenites in medium-Mn steel has not been fully studied. In this manuscript, we advance our previous work on crystal plasticity simulation based on the Taylor model to consider fully resolved high-fidelity microstructures and systematically study the influence of the UFG austenites. The original microstructure with UFG is reconstructed from a set of serial electron backscatter diffraction (EBSD) scans, where the exact grain morphology, orientation, and phase composition are preserved. This microstructure was further analyzed to identify the UFG austenites and recover them to their parent martensite before the intercritical annealing. These two high-fidelity microstructures are used for a comparative study using dislocation density-based crystal plasticity finite modeling to understand the impact of UFG austenites on both the local and overall mechanical responses.

Austenite formation in a medium-Mn steel during intercritical annealing via in situ high-energy X-ray diffraction

The microstructural evolution of a prototype Fe-0.15C-5.56Mn-1.1Si-1.89Al medium-Mn third-generation advanced high strength steel (3G AHSS) with a martensite-ferrite (MF) starting microstructure during intercritical annealing was determined in situ using high energy X-ray diffraction (HEXRD). Intercritical annealing was carried out at 665 °C and 710 °C for 120 s and 240 s, followed by cooling to room temperature. HEXRD data were analyzed to monitor the austenite fraction and lattice parameters throughout the thermal cycle. During isothermal holding, the austenite fraction increased, up to 31% and 45% for the samples annealed for 120 s, and up to 33% and 46% for the samples annealed for 240 s at 665 °C and 710 °C, respectively. Observed changes in lattice parameters during isothermal holding were attributed to composition changes due to the partitioning of C between austenite and ferrite. Diffusion simulations using DICTRA were used to calculate solute partitioning during intercritical annealing, providing further insights into both austenite growth and the distribution of alloying elements within the austenite.

Unraveling the impact of the substitution of Si by Al on liquid metal embrittlement behavior of 3rd generation AHSS

This study addresses one of the most crucial ongoing discussions concerning the mitigation of Zinc-induced Liquid Metal Embrittlement (LME) in third-generation Advanced High-Strength Steels (AHSS). The role of Silicon (Si) and Aluminum (Al), both common alloying elements in AHSS, in triggering LME-induced cracking is thoroughly investigated. Two chemical compositions, 0.2C–3Mn-0.8Si and 0.2C–3Mn–1Al, featuring martensitic microstructures, were selected. Hot tensile tests were conducted in the temperature range of 600–900 °C to simulate the thermomechanical cycle during spot welding.This resulted in a significant reduction in ductility for both Si and Al-alloyed steels in the coated samples compared to the uncoated ones. The loss of ductility was notably more pronounced in Si-alloyed steel than in Al-alloyed steel. These findings were also evident in a specialized LME-triggering spot-welding test, suggesting that Si, as an alloy element in steel, leads to higher LME susceptibility compared to Al. This can be attributed, as indicated by thermodynamic equilibrium calculations and investigations of the Zn–Fe layer, to an increased destabilization and retardation of the protective intermetallic Zn–Fe phases by Si. The insolubility of Si in intermetallic phases and liquid Zn is considered a thermodynamic constraint.In contrast, the theoretically possible full solubility of 1% Al in intermetallic phases as well as in liquid Zn was experimentally demonstrated and supported by thermodynamic simulation. Furthermore, Al, by increasing the Ac3 temperature, results in lower amounts of austenite in the microstructure. It is known that austenite plays a detrimental role in triggering LME. Based on this comprehensive study, it is reasonable to conclude that the formation of intermetallic phases plays a critical role in controlling the contact time between steel and liquid Zn as an embrittling agent, and this is strongly influenced by the Si and Al content of the steel.

Process Maps for Predicting Austenite Fraction (vol.%) in Medium-Mn Third-Generation Advanced High-Strength Steels.

Process maps were developed using a combination of microstructural analysis and DICTRA-based modeling to predict the austenite vol.% as a function of the intercritical annealing parameters and starting microstructure. The maps revealed a strong dependence of the calculated austenite fraction (vol.%) on the Mn content (4-12 wt.%) and intercritical annealing temperatures (600 °C to 740 °C). The calculations were carried out for constant carbon, Al, and Si contents of 0.2 wt.%, 1.5 wt.%, and 1.0 wt.%, respectively. A modified empirical equation proposed by Koistinen and Marburger was employed to calculate the room-temperature retained austenite vol.% as a function of the intercritical annealing temperature, including the effect of the austenite composition. The process maps offer valuable insights for designing intercritical treatments of medium-Mn steels, aiding in the optimization of steel properties for automotive applications.

Microstructural Design and Mechanical Enhancement of δ-TRIP Steel Through Mo Micro-alloying and Isothermal Bainitic Transformation

This research was done to investigate third-generation Advanced High-Strength Steel (AHSS) to improve mechanical properties and reduce production costs in the automotive industry. The potential of TRIP-assisted steel has been studied to address this issue, with a special focus on δ-TRIP steels. This research studied the δ-TRIP samples, which were micro-alloyed with 0.05 and 0.30 wt.% Mo, with isothermal bainitic transformation (IBT) time parameters. Microstructural analyses were conducted using optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectrometry (EDX). The volume percentage of retained austenite (RA) phase, critical to achieving the requisite mechanical characteristics, was determined using X-ray diffraction (XRD). The analysis of the samples revealed a complex, multi-phased structure comprising δ-ferrite matrix, α-ferrite, bainite, RA, and martensite. The quantity and morphology of RA significantly influenced the resulting mechanical characteristics. The experimental results demonstrated yield stresses (YS) of 400–440 MPa, ultimate tensile strength (UTS) of 790–870 MPa, and total elongations to failure (TEL) of 24–34% in δ-TRIP steels containing 0.05 and 0.30 wt.% Mo alloy. The optimal combination of UTS and TEL (UTS × TEL) is achieved at an impressive 850 MPa × 32% (27200 MPa.%). This remarkable achievement was made possible by adding only 0.30 wt.% Mo and IBT, which were carried out at 450°C for 10 min. Focusing on the effects of Mo-alloy content and heat treatment duration on microstructure and mechanical characteristics, this study provided insights into enhancing the quality of δ-TRIP steel while decreasing manufacturing costs.

Evaluation of microstructures and mechanical properties of deltha trip steel with different vanadium contents

This research studies the effect of adding 0.12 and 0.25 wt% vanadium on the microstructure and mechanical properties of a delta-TRIP steel. Optical microscopy and scanning electron microscope (SEM) were employed to investigate the microstructure of the steel. In addition, hardness measurements and tensile testing were used for the evaluation of the mechanical properties. The X-ray diffraction (XRD) analysis was also applied to analyze the present phases. The structure of the three studied steels before applying the heat treatment cycle consisted of delta-ferrite, allotriomorphic ferrite, martensite, and pearlite. The heat treatment cycle led to the stability of the austenite phase. The addition of 0.12 wt% V resulted in the enhancement of the mechanical properties so that the best combination of strength (866 MPa) and elongation percentage (41 %) was achieved in this steel. Nonetheless, the addition of 0.25 wt% V deteriorated the mechanical properties since the increase in the vanadium content promoted the formation of martensite, decreased the percentage of the retained austenite, and weakened the mechanical properties. However, adding 0.12 wt% V improved the mechanical properties since it increased the strength through solid-solution strengthening and precipitation hardening; no brittle martensite was formed, and lamellar δ-ferrite was achieved. The steel containing 0.12 wt% V, exhibiting a formability index of 35.7 GPa%, is in the range of the third-generation advanced high-strength steels.

Mechanical behavior investigation for quenching and partitioning steel dissimilar resistance spot welds

Resistance spot welding is still the most common joining process for autobody structure assembly. It has many advantages and is simple to use, but the main challenge is controlling the process parameters that affect mechanical properties and weld quality. Advanced high-strength steels were developed to meet the demands of automakers such as lighter and stronger autobody. Quenching and partitioning (Q&P 980) steel is a third-generation advanced high strength steel with a combination of high strength and high ductility. In this study, effect of resistance spot welding parameters on the mechanical performance of dissimilar combination of Q&P980 steel and SPFC780Y high strength steel was investigated. Welding current, welding time, electrode pressure and holding time were chosen as the most important process parameters influencing the weld quality. A comprehensive investigation was conducted on geometrical attributes such as nugget size, fusion zone width, fusion zone area, electrode indentation and heat affected zone area and their correlations with peak load (Pmax), failure energy, fracture energy, and elongation at peak load (Lmax). In contrast the failure modes and fracture behavior were studied using scanning electron microscopy. It was observed that using high levels of welding current and welding time while maintaining low levels of electrode pressure and holding time result in a maximum peak load, energy absorption and maximum (Lmax) with pullout failure mode (PF) and this was demonstrated for large nugget size to a critical limit. The methods and findings of this research can be used as a basis for further research and development in the field of dissimilar resistance spot welding.

Resistance spot welding behaviour of novel medium manganese (M-Mn) steels - Role of welding parameters on weld microstructure and mechanical properties

Medium Mn (M-Mn) steels are classified as third-generation advanced high-strength steels (3G-AHSS) and have demonstrated outstanding mechanical properties. As a result, they are being considered as potential materials for use in the automotive industry. Spot weldability of materials is an essential requirement for the body in white (BIW) structures in automotive vehicles. Resistance spot welding (RSW) M-Mn steel can be challenging because it can lead to the formation of a fully martensitic microstructure. This work established the weld growth curve on M-Mn steel in the 4 to 8 kA current range. Based on this, single pulse (6 kA) and double pulse current (first pulse of 6 kA followed by the second pulse of 4 to 7 kA) were employed to investigate the microstructure, elemental segregation, cross-tensile strength (CTS), and fracture behaviour of the M-Mn steel welds. These welds, in all conditions, exhibited a martensitic microstructure with retained austenite content of <10 %. In all welding conditions, martensite softens along the heat-affected zone (HAZ) boundary, yielding tempered martensite and carbides. A study of chemical homogeneity using electron probe microanalysis (EPMA) demonstrated that Mn and Si segregate along the weld nugget (WN) edge during single (6 kA) and double (6–6 kA and 6–7 kA) pulsing. Mn and Si segregation is less prominent in double pulse welds at lower pulse currents (<6–6 kA). The elemental segregation at higher pulse currents is higher due to the more pronounced thermal gradient within the weld nugget, which promotes elemental segregation at the interface. Based on the cross-tension test results, the double pulse welds (6–7 kA) had the maximum CTS (1.26 kN) and energy absorption (2 J). The failure mode in this condition is a predominantly partial interfacial failure (PIF) with a plug ratio of about 50 %. This is attributed to the larger nugget diameter and refined martensitic structure. Complete interfacial failure (IF) leading to interdendritic fracture and a plug ratio of 0 % was observed when two equal pulse currents (6–6 kA) were applied. This can be attributed to remelting of WN and a high degree of Mn and Si segregation. From the above studies, we can conclude that M-Mn steel is weldable; however, further strategies are necessary to enhance the CTS of M-Mn steel welds.

Edge fracture of the first and third-generation high-strength steels: DP1000 and QP1000

Advanced high-strength steels (AHSS) have shown profound progress in improving tensile ductility or global formality in the last decades over three generations. For a complete assessment of both the global and local formability, this study aims to characterize and compare the tensile and edge fracture behavior of the first and third-generation AHSS (dual-phase steel and quenching & partitioning steel) with the same nominal strength level of 980 MPa. Uniaxial tensile tests are performed to characterize the tensile properties. Hole expansion tests are conducted with two edge conditions based on separated preparation techniques (waterjet with polishing and punching) to investigate the edge fracture for both materials. The hole expansion ratios and edge fractures are compared between two materials and two edge conditions. It is concluded that the investigated QP1000 has promoted global formability while the DP1000 shows better local formability due to its damage-tolerant and crack-resistant responses.

Effect of Liquid Metal Embrittlement Indent Cracks on Zinc Coated 3rd Generation AHSS Mechanical Performance

Third-generation advanced high-strength steels (3G-AHSS) are typically galvanized to prevent corrosion of the outer body structure. However, the zinc coating on the surface, combined with the locally elevated temperatures generated during the resistance spot welding (RSW) process, can provide the prerequisites for liquid metal embrittlement (LME). This work uses two strategies to control LME crack formation: current pulsation and varying the electrode geometry. These two methods were compared to a baseline welding schedule for a 3G-980-GI coated AHSS. The effectiveness of each method was discussed in terms of the overall weld cracking index and local cracking index. The results showed that increasing the current pulses results in a slower energy input into the weld, which can help to reduce LME crack formation. Introducing more pulses (five to seven pulses) reduced LME crack formation while maintaining the same welding time. Regarding the electrode geometry, the results showed an increase in LME cracking index for currents below the expulsion level Imax-10% when the electrode face diameter increased, whereas at the current level Imax-200A, the electrode radius was the most important factor to control LME crack index. For the current level above the expulsion, Imax+10%, a drastic decrease in the LME cracking index was observed when a large electrode surface diameter was used. The electrode radius was not a significant factor in controlling LME. The mechanical properties of selected conditions were examined using the lap shear test and the results showed no significant effect of LME cracks on the shear tensile strength. The location of the failure indicated that most of the cracks are located in the indented area (type A), which does not influence the lap shear strength.

Effect of Si on the dislocation state within martensite of ultra-high strength hot-rolled medium Mn steel with good ductility

Medium Mn steels are promising candidates for the third-generation advanced high-strength steels due to their good combination of ultimate tensile strength (UTS) and total elongation after fracture (TEL). Most investigations of medium Mn steels focused on the volume fraction of retained austenite (RA) and stability of RA; however, the strengthening phase martensite was paid little attention to. The present study systematically investigated the effect of Si on the deformation behavior of martensite in 0.2C–6.8Mn-(0, 2, 4)Si (wt. %) hot-rolled medium Mn steels without any heat treatment. The UTS and TEL of the 4Si hot-rolled medium Mn steel are 2163 MPa and 11.7%, respectively, which is rare in the existing hot-rolled medium Mn steels. All three hot-rolled steels had practically equal fraction and mechanical stability of RA, so that the influence of Si on the evolution of martensite fine structure and the nature of the ultra-high UTS and good ductility during deformation could be revealed. By combining the X-ray and neutron diffraction techniques, it was found that the addition of Si increased the dislocation density, especially screw dislocations, and decreased the crystallite size within martensite. The ultra-high UTS originates from the enhanced strain hardening rate caused by the Si alloying, high dislocation density and possibly increased number of martensite lath boundaries and dislocation cell formation. The good ductility mainly stems from the formation of dislocation cell structure due to the addition of Si causing dislocations to be mostly of screw type. The dislocation cells can also improve the strain hardening rate. This work opens a new pathway towards tailoring the dislocation state within martensite for substantially enhanced the mechanical properties of hot-rolled medium Mn steels.

On the Selective Oxidation of a 0.15C-6Mn-2Al-1Si Third-Generation Advanced High Strength Steel During Two-Stage Annealing Treatments

On the Selective Oxidation of a 0.15C-6Mn-2Al-1Si Third-Generation Advanced High Strength Steel During Two-Stage Annealing Treatments

Effects of Partial Replacement of Si by Al on Cold Formability in Two Groups of Low-Carbon Third-Generation Advanced High-Strength Steel Sheet: A Review

Partial replacement of Si by Al improves the coatability (or galvanizing property) of Si-Mn advanced high-strength steel (AHSS) sheets. In this paper, the effects of the partial replacement on the microstructure, tensile property, and cold formability are reported for the low-carbon third-generation AHSS sheets, which are classified into two groups, “Group I” and “Group II”. The partial replacement by 1.2 mass% Al increases the carbon concentration or mechanical stability of retained austenite and decreases its volume fraction in the AHSSs, compared to Al-free AHSSs. The partial replacement deteriorates the tensile ductility and stretch formability in the AHSSs with a tensile strength above 1.2 GPa. On the other hand, it achieves the same excellent stretch-flangeability as Al-free AHSSs. A complex addition of Al and Nb/Mo further enhances the stretch-flangeability. The cold formabilities are related to the heat treatment condition and microstructural and tensile properties, and the stress state.

A comprehensive evaluation of tempering kinetics on 3rd generation advanced high strength steels

Emerging third-generation advanced high strength steels (3G AHSS) grades are being increasingly considered for autobody applications owing to their complex microstructures providing an excellent combination of strength and ductility. When welded with RSW, 3G AHSS such as 3G 1180 and 3G 980, exhibits a solid-state transformation in the sub-critical-heat-affected-zone (SCHAZ) due to the heat generated during the RSW process. The resulting changes in microstructure can affect the mechanical properties of the material within and around the spot welds and thereby influence the performance of welded components in case of a vehicle crash event. To study metallurgical transformations in the SCHAZ during the RSW process, 3G 1180 and 3G 980, and a reference martensitic press hardened steel, PHS 1500, were selected. These materials were subjected to isothermal tempering experiments at temperatures ranging between 350 °C and 650 °C and different tempering times from 0.2 s to 24 h. It was shown that the Hollomon-Jaffe model accurately describes the tempering kinetics of 3G 1180 and PHS 1500 but does not predict the transformation processes in the SCHAZ of 3G 980. The PHS 1500 and 3G 1180 showed softening (tempering) for all combinations of investigated tempering times and temperatures due to the decomposition of martensite. In contrast, the 3G 980 showed a combination of softening by the formation of martensite and secondary ferrite combined with secondary hardening due to the formation of fine M2C typed plate-like carbides. Furthermore, during long tempering, the M2C particles dissolve into the matrix and were replaced by cementite particles in 3G 980.

Resistance Spot Welding of Quenching and Partitioning (Q&amp;P) Third-Generation Advanced High-Strength Steel: Process–Microstructure–Performance

Resistance Spot Welding of Quenching and Partitioning (Q&amp;P) Third-Generation Advanced High-Strength Steel: Process–Microstructure–Performance

Cyclic intercritical annealing to improve strength-ductility combinations in medium manganese steels

With the push for superior properties from third-generation advanced high-strength steels, particularly by the automotive industry, medium manganese steels have emerged as a viable candidate. Intercritical annealing of medium manganese steels promotes retention of large austenite fractions (>30%) at room temperature. While prior studies have established strong mechanical property dependence on the amount and mechanical stability of retained austenite, the effect of austenite distribution on mitigating local strain incompatibility has received less attention. The present study proposes a method to alter phase distribution: a novel cyclic intercritical annealing that promotes nucleation and efficient stabilization of retained austenite. Grain sizes were found to be comparable between isothermal- and cyclic-annealed samples, yet bulk neutron diffraction revealed greater austenite fractions in the latter, indicating more extensive austenite nucleation. Combining the cycle with an isothermal hold facilitated austenite growth and enrichment, improving work hardening while maintaining toughness relative to purely isothermal annealing.

Tailoring retained austenite and mechanical property improvement in Al–Si–V containing medium Mn steel via direct intercritical rolling

Medium Mn steels are promising candidates for the third-generation advanced high strength steels. However, it shows a distinct limit of mechanical property under conventional hot-rolling and intercritical annealing procedures. Aiming at improving the combination of strength, ductility and toughness, the present study proposed a multi-alloyed design principle together with a direct intercritical rolling process. The results show that the microstructure of the hot rolled steel consisted of wide delta ferrite, lath martensite, twinned-martensite and coarse retained austenite with a low stability, corresponding to a product of strength and elongation (PSE) of 24.0 GPa% and an impact toughness of 13.8 J/cm2 at −40 °C. In contrast, the intercritical rolling produced a laminated microstructure containing thin delta ferrite, submicron recrystallized ferrite and retained austenite. The PSE and impact toughness at −40 °C simultaneously increased to 46.1 GPa% and 46.7 J/cm2, respectively, which was also much higher than the hot rolled steel subjected to low temperature and high temperature annealing. The significant enhancement of mechanical property was mainly attributed to the highest content and optimal stability of retained austenite caused by the submicron grain size, high density of dislocations, granular morphology, and elemental enrichment. The optimized austenite stability provided persistent transformation-induced plasticity (TRIP) effect for work hardening and damage resistance. Moreover, the nano-sized VC precipitates in the intercritical rolled steel played a significant role in reaching an ultrahigh yield strength of ∼1 GPa. This study not only provides a very simple pathway to improve the mechanical property of medium Mn steel, but also sheds light on the design and development of high-performance materials.

The Influence of Electrode Indentation Rate on LME Formation during RSW

During resistance spot welding of zinc-coated advanced high-strength steels (AHSSs) for automotive production, liquid metal embrittlement (LME) cracking may occur in the event of a combination of various unfavorable influences. In this study, the interactions of different welding current levels and weld times on the tendency for LME cracking in third-generation AHSSs were investigated. LME manifested itself as high-penetration cracks around the circumference of the spot welds for welding currents closely below the expulsion limit. At the same time, the observed tendency for LME cracking showed no direct correlation with the overall heat input of the investigated welding processes. To identify a reliable indicator of the tendency for LME cracking, the local strain rate at the origin of the observed cracks was analyzed over the course of the welding process via finite element simulation. While the local strain rate showed a good correlation with the process-specific LME cracking tendency, it was difficult to interpret due to its discontinuous course. Therefore, based on the experimental measurement of electrode displacement during welding, electrode indentation velocity was proposed as a descriptive indicator for quantifying cracking tendency.

Experimental characterization and modeling of complex anisotropic hardening in quenching and partitioning (Q&P) steel subject to biaxial non-proportional loadings

Quenching and partitioning (Q&P) steels, as one of the third-generation advanced high strength steels, exhibit complex anisotropic hardening behavior under biaxial non-proportional loadings. In this study, a wide range of strain path changes (SPCs) defined as an angle (χ) between stress deviators before and after the SPC is experimentally applied to characterize the anisotropic hardening of a Q&P steel with a strength grade of 980 MPa (QP980). The investigated SPCs include uniaxial tension followed by compression (UT-UC; χ=180°), uniaxial compression followed by tension (UC-UT; χ=180°), uniaxial tension followed by plane strain (UT-PS; χ=30°), equi-biaxial tension followed by plane strain (EBT-PS; χ=30°), followed by uniaxial tension (EBT-UT; χ=60°) and followed by simple shear (EBT-SH; χ=90°). These SPCs are achieved by the program-controlled biaxial tensile testing equipment using novel arm-reinforced cruciforms. The experimental findings in the QP980 steel sheet are summarized as follows: (1) Strong strain-dependent Bauschinger effect, transient hardening and permanent softening are observed in both UT-UC and UC-UT loadings; (2) Bauschinger effect increases as strain increases, and it exhibits obvious tension-compression asymmetry; (3) The transient hardening behaviors are path-dependent under SPCs with various χ; (4) The Bauschinger coefficient is approximately a parabola function of cosχ; (5) The most significant strength softening occurs under EBT-SH loading. In order to describe the complex hardening behavior of the QP980 steel, a distortional hardening model is proposed on the basis of non-associated flow rule. A coupled quadratic and stress-invariant-based yield function is used to describe stress anisotropy, strength differential effect, and anisotropic hardening for proportional loadings. Then, the Bauschinger effect related hardening and path-dependent permanent softening are captured by a modified homogeneous anisotropic hardening model. The calibrated model parameters and experimental validations demonstrate that the strain- and path-dependent Bauschinger effect can be well predicted by the proposed constitutive model. Especially, the model enables to accurately describe both the asymmetric anisotropic hardening and yield surface distortions of the QP980 steel at various biaxial SPCs.