Clarifying the Role of Welding Speed and Zr Addition on Microstructure and Mechanical Properties of Laser‐Welded Joint of Complex Phase Steel With High Formability

The development of automotive steel needs high strength and plasticity, excellent forming and welding performance. Complex phase steel with high formability (CH steel) is a promising steel used for automotive structural components due to its high strength and excellent formability. This paper investigates the effect of welding speed and Zr addition on the microstructure evolution and mechanical properties of welded joints produced by laser welding via analyzing microstructure morphology, crystal characteristics, hardness distribution, mechanical behavior and in situ corrosion behavior. The experimental results indicate that the microstructure, crystal characteristics, and hardness in the FZ of prepared welded joints of CH steel are not affected by welding speed. Zr addition promotes the FZ microstructure transformation from martensite to ferrite with Zr–C‐rich precipitates. The FZ hardness of Zr‐added welded joint is lower than that of Zr‐free welded joint. The mechanical deformation characteristics of prepared welded joints shows weak dependence on welding speed. The mechanical strength of prepared welded joints is higher than that of base material. However, Zr addition degrades the mechanical strength of laser‐welded joint of CH steel due to the intrinsic weak strength of ferrite in FZ. The FZ of Zr‐added welded joint shows weak corrosion resistance at early corrosion stage.