Study on microstructure evolution and mechanical properties of high-strength low-alloy steel welds realized by flash butt welding thermomechanical simulation

Defects would occur in the weld joint of the wheel rims during the post-flash butt welding (FBW) process suffering from poor plasticity, which will deteriorate the quality and lifecycle of finish products. Therefore, the FBW process of the 440CL high-strength-low-alloy (HSLA) steel was physically simulated and the influence of flash parameters on FBW joints was systematically evaluated in this study. The results showed that the width of heat affected zone increased with accumulated flash allowance (delta(f)) while declined with accelerated flash speed (v(f)). The recrystallization level would be intensified with increased delta(f). Meanwhile, the acceleration in v(f) populated the WZ with a more homogeneous microstructure, higher recrystallization degree and lower dislocation density. The hardness in WZ slightly reduced (202 -> 195 HV) as increased delta(f) but obviously dropped (192 -> 177 HV) as increased delta(f). All tensile samples were fractured at the BM location and the tensile properties of FBW joints exhibit a good match with those of BM, with a slight increase in strength (UTS: 468 493 MPa; YS: 370 similar to 403 MPa) but a mild decrease in plasticity (EL: 39 similar to 44%; RA: 74 similar to 79%). Furthermore, both the joint strength and ductility showed a downward tendency with the increment of delta(f). However, the strength slightly decreased while the ductility increased with the advancement of v(f). These findings would be valuably referential to the real FBW of HSLA steels with optimized microstructure and mechanical performance.

Automated summary

This study simulated the FBW process of 440CL high-strength-low-alloy steel and systematically evaluated the influence of flash parameters on the weld joint. The results showed that the width of heat affected zone increased with accumulated flash allowance while declined with accelerated flash speed. The recrystallization level would be intensified with increased accumulated flash allowance, and the acceleration in flash speed populated the weld zone with a more homogeneous microstructure.