Microstructures and Toughness of Weld Metai of Ultrafine Grained Ferritic Steel by Laser Welding

Kudong ZHANG, Wuzhu CHEN, Cheng WANG, Lin ZHAO Yun PENG and Zhiling TIANDepartment of Mechanical Engineering, Tsinghua University, Beijing 100084, ChinaCentral Iron & Steel Research Institute, Beijing 100081, China

摘 要：<正>3 mm thick 400 MPa grade ultrafine grained ferritic steel plates were bead-on-plate welded by CO2 laser with heat input of 120-480 J/mm. The microstructures of the weld metal mainly consist of bainite, which form is lower bainite plates or polygonal ferrite containing quantities of dispersed cementite particles, mixed with a few of low carbon martensite laths or ferrite, depending on the heat input. The hardness and the tensile strength of the weld metal are higher than those of the base metal, and monotonously increase as the heat input decreases. No softened zone exists in heat affected zone （HAZ）. Compared with the base metal, although the grains of laser weld are much larger, the toughness of the weld metal is higher within a large range of heat input. Furthermore, as the heat input increases, the toughness of the weld metal rises to a maximum value, at which point the percentage of lower bainite is the highest, and then drops.

关键词：