Research on the High-Temperature Deformation Mechanism and Welded Seam Constitutive Relationship for High-Strength Steel

To investigate the deformation mechanism of hot-forming high-strength steel laser tailor-welded blanks (TWBs) and base metal, the hot tensile experiments were carried out at various temperatures and strain rates. The macroscopic mechanical properties of base metal and TWBs were analyzed. Based on the experimental analysis, the Norton–Hoff (N–H) constitutive models of Usibor1500 and Ductibor500 were established, respectively. A new calculation method for the stress–strain relationship of welded seams at high temperatures is proposed. On this basis, the constitutive model of high-temperature welded seam is established. Microstructure evolution during thermal deformation at 700 °C–0.1 s⁻¹ was investigated by electron backscatter diffraction (EBSD). The results show that the variation of grain size, Schmidt factor, and dislocation density causes a change in the macroscopic mechanical properties of high-strength steel. A high-temperature tensile numerical simulation model is based on the constitutive relation model of the base metal and welded seam established above. According to the AARE and R values comparison, the new constitutive model of high-temperature welded seam has high fitting accuracy with an AARE of 1.4 pct and an R-value of 0.99.