Microstructure- and Strain Rate-Dependent Tensile Behavior of Fiber Laser-Welded DP980 Steel Joint

Journal of Materials Engineering and Performance
February 2016, Volume 25, Issue 2, pp 668-676

Qiang Jia (1), Wei Guo (1), Peng Peng (1) (2), Minggao Li (3), Ying Zhu (1), Guisheng Zou (4)

Show Affiliations

1. School of Mechanical Engineering and Automation, Beihang University, Xue Yuan Road No.37, Haidian District, Beijing, 100191, China
2. Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
3. Chinese CNR Tangshan Railway Vehicle Limited Liability Company, Tangshan, 063020, China
4. Department of Mechanical Engineering, Tsinghua University, Beijing, 100084, China

 

Abstract
DP980 steels were butt-welded by fiber laser welding. The microstructures, microhardness distribution, and tensile behavior of the joint were investigated. The results showed that the fusion zone (FZ) consisted of fully martensite with higher hardness compared to the base metal (BM). A softened zone (20 HV0.2 drop) was produced in heat-affected zone due to martensite tempering during the laser welding. The ultimate tensile strength (UTS) and yield strength (YS) of the laser-welded joint were not degraded compared to BM with the existence of softened zone. The UTS and YS of the welded joint increased with the increase of tensile strain rate. The work hardening exponents of the BM and welded joint showed weak positive strain rate dependence. The deformation of softened zone was restrained by the hardened FZ during loading, resulting in a higher work hardening rate of softened zone than that of BM. The failure of welded joint occurred in the BM instead of softened zone. The fracture surfaces of the joint exhibited typical ductile fracture over strain rate from 0.0001 to 0.1 s−1.

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