Evolving asymmetric yield surfaces of quenching and partitioning steels: Characterization and modeling

Quenching and partitioning (Q&P) steel plays a significant role in automotive lightweighting on the merits of high strength and good ductility. Yield behavior of Q&P steels with strength grades of 1180 MPa (QP1180) and 980 MPa (QP980) and one dual-phase steel (DP980) were characterized under various proportional loading, i.e., uniaxial tension, uniaxial compression, simple shear and biaxial tension utilizing cruciforms with arms reinforced by laser deposition, i.e., an additive manufacturing process. Results show that QP1180 and QP980 exhibit pronounced strain hardening, strength differential effect and anisotropic hardening rather than DP980. The Karafillis and Boyce (1993) yield criterion was modified and further employed to construct a multiplicative yield criterion under non-associated flow rule. Anisotropic hardening is captured by directly employing the stress vs. strain curves under uniaxial tension, uniaxial compression and equi-biaxial tension. Besides, a user-friendly calibration strategy was proposed to identify the shape-dominating parameters in the developed yield criterion utilizing the flow stresses under plane strain and simple shear. Finally, evolving asymmetric yield surfaces of the two investigated Q&P steels were accurately described by the developed yield criterion.

Automated summary

The yield behavior of different strength grades of Q&P steel and dual-phase steel were compared, showing that Q&P steels exhibit significant strain hardening and anisotropic hardening, while the dual-phase steel does not have these characteristics. Furthermore, a modified yield criterion was developed under non-associated flow rule to accurately describe the asymmetric yield surfaces of the investigated Q&P steels.