Computational material design for Q&P steels with plastic instability theory

Abstract

The ultimate tensile strength (UTS) and uniform elongation (UE) of quenching and partitioning (Q&P) steels under tension were examined with a combined theoretical, experimental and computational approach. The constituent phase properties of various Q&P steels were first estimated based on in situ high-energy X-ray diffraction (HEXRD) tensile tests under the quasi-static strain rate and room temperature. Plastic instability theory with the rule of mixtures (ROM) was then applied to the obtained phase properties to estimate the UTS/UE of the Q&P steels. A parametric study was also performed to examine the effects of various material parameters on the UTS/UE of Q&P steels. Computational material design was subsequently conducted based on the information obtained from the parametric study. The results showed that the plastic instability theory with iso-stress-based ROM may be used to estimate the UEs of the evaluated Q&P steels. The results also indicated that higher austenite stability/volume fractions, less strength difference between the primary phases, and higher hardening exponents of the constituent phases are generally beneficial for performance improvement of Q&P steels, and various material parameters may be concurrently adjusted in a cohesive way to improve performance of Q&P steel.