Among the three typical stainless steels of austenite, martensite and ferrite, the weldability of austenitic stainless steel is better. 301L stainless steel is a steady-state austenitic stainless steel. After solution heat treatment, it exhibits a single-phase austenite structure at room temperature. However, its welding performance, especially arc welding performance, is still far behind other car body materials, which is mainly restricted by the following two physical properties:
1. The thermal expansion coefficient is large. The thermal expansion coefficient of stainless steel is about 1.5 times that of carbon steel, which makes the deformation of the same heat during welding much larger than that of ordinary steel.
2. Low thermal conductivity, about 1/3 of carbon steel. Therefore, the heat generated by welding cannot be dissipated quickly, and a large amount of heat is concentrated in the weld area. However, the austenite structure in stainless steel is unstable at high temperature. At 500°C to 800°C, Cr carbides in the steel will precipitate along the grain boundaries, resulting in grain boundary corrosion near the grain boundaries due to the decrease in the Cr content. , while the yield strength and tensile strength will drop sharply [2].
Therefore, 301L stainless steel plate should try to avoid the damage of appearance and corrosion resistance caused by arc welding, and the spot welding process with small heat input is generally used.