J Mater Sci Technol ›› 2004, Vol. 20 ›› Issue (06): 755-759.

• Research Articles • Previous Articles     Next Articles

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

Xudong ZHANG, Wuzhu CHEN, Cheng WANG, Lin ZHAO, Yun PENG, Zhiling TIAN   

  1. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China...
  • Received:1900-01-01 Revised:1900-01-01 Online:2004-11-28 Published:2009-10-10
  • Contact: Xudong ZHANG

Abstract: 3 mm thick 400 MPa grade ultrafine grained ferritic steel plates were bead-on-plate welded by CO¬2 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.

Key words: Laser welding, Ultrafine grained steel, Microstructure, Toughness