Microstructure and mechanical properties of fiber laser welded QP980 steel

• Published in: Journal of materials processing technology 2018-06, Vol.256, p.229-238
• Main Authors: Guo, Wei, Wan, Zhandong, Peng, Peng, Jia, Qiang, Zou, Guisheng, Peng, Yun
• Format: Article
• Language: English
• Subjects: Base metal; Crack propagation; Data analysis; Digital image correlation (DIC); Ductile fracture; Elongation; Energy absorption; Fatigue cracks; Fatigue failure; Fatigue limit; Fatigue properties; Fiber lasers; Fracture mechanics; Heat affected zone; High strain rate; Laser beam welding; Laser welding; Lasers; Martensitic stainless steels; Mechanical properties; Microstructure; QP steels; Steel; Strain rate; Stress concentration; Striations; Tempered martensite; Tensile strength; Welding
• ISSN: 0924-0136; 1873-4774
• DOI: 10.1016/j.jmatprotec.2018.02.015

The fusion zone of laser welded QP980 composed of fully martensitic structure exhibited high hardness (493 Hv). The sub-critical heat affected zone contained partially tempered martensite with a hardness drop (21 Hv). The joints and base metal showed positive strain rate dependent tensile strength, yield strength and energy absorption in dynamic strain rate regime, while elongation responded differently because of thermal softening effect. All the joints failed at base metal showing a typical ductile fracture. Fatigue limit of the joints was lower than that of base metal (171 MPa and 261 MPa, respectively). Fatigue specimens of joints failed at weld area because of their higher sensitivity to stress concentration than base metal. Fatigue crack originated from the specimen surface, and propagated through fatigue striations together with secondary cracks.