Effects of notch position on the fatigue crack growth behavior of dissimilar laser welded DP980/QP980 joint

• Published in: Fatigue & fracture of engineering materials & structures Vol. 45; no. 4; pp. 1111 - 1125
• Main Authors: Huang, Jiajin, Li, Shengci, Zhong, Huilong, Li, Dehua, Zhang, Zhiqian
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01.04.2022
• Subjects: advanced high‐strength steel; Automobile industry; Crack closure; Crack propagation; Ductile fracture; fatigue crack growth; Fatigue failure; Fiber lasers; Fracture mechanics; Heat affected zone; Heat treating; High strength steels; Inhomogeneity; Laser beam welding; laser welding; Lasers; Mechanical properties; Microstructure; Stress-strain curves; Work hardening
• ISSN: 8756-758X; 1460-2695
• DOI: 10.1111/ffe.13653

Laser welding of heterogeneous high‐strength steels (AHSSs) is increasingly used in the automotive industry, while the inhomogeneous microstructure of the joint could affect its fatigue crack growth (FCG) behavior. Therefore, fiber laser welding experiments were performed in this study to evaluate the microstructure, mechanical properties, and effects of notch position on FCG behavior of dissimilar laser welded DP980/QP980 joint. Results show that the hardness of fusion zone (FZ) near the QP980 side was higher and softening zones were observed in the heat affect zone (HAZ) on both sides of the joint. The stress–strain curves of all the samples show continuous yield and follow the two‐stage work hardening mechanism. The weld overmatch effect induced by laser welding could hinder the propagation of fatigue crack. The microstructural inhomogeneity, weld mismatch effect, and crack closure contribute to the variety of FCG rates. Ductile fracture mechanism became more dominant with the increase of ΔK. Highlights The hardness of FZ near QP980 side was higher, softening occurred in HAZ of both sides of joint. All the stress–strain curves show continuous yield and follow two‐stage work hardening mechanism. Microstructural inhomogeneity, weld mismatch effect, and crack closure affect the FCG rates.