Factors Affecting Mechanical Properties of Laser Welded Joint of 400 MPa Grade Ultra-Fine Grained Ferrite Steel

摘要

This paper investigated the laser weldability and the factors affecting the mechanical properties of the laser welded joint of 400 MPa ultra-fine grained steel. Although the grain of welded joint (weld and HAZ) has largely grown up under usual laser welding conditions, the strength and toughness of the welded joint are much higher than those of base metal. The microstructure (either weld metal or HAZ) mainly consists of lower bainite, mixed with some low carbon martensite or ferrite, depending on the heat input. The cleanness of ferrite steel has also greater effect on the toughness of the welded joint than the grain size. In specific, controlling the S, Si and Mn content of base-metal is very significant for the toughness of the joint.