Enhancement of mechanical properties of electron beam-welded D6ac steel tube

Abstract

A forward flow-formed D6ac steel tube was joined through the electron beam welding process and was then subjected to post-weld heat treatment. The mechanical properties and hardness profiles of the as-welded (without heat treatment after welding) steel and different post-weld heat treatment weldments were investigated. The results show that the as-welded D6ac steel exhibited very poor mechanical strength and elongation. After post-weld heat treatment, a large improvement in the mechanical properties of the weldment was achieved. Forward flow-formed D6ac electron beam weldment subjected to post-weld heat treatment at 350 degrees C reached the largest yield strength and ultimate tensile strength values (approximately 1359.2 and 1494.3 MPa, respectively). Forward flowformed D6ac electron beam weldment subjected to post-weld heat treatment at a temperature of 650 degrees C exhibited an overtempered state, which led to mechanical strength and hardness deteriorations of the weldment. This study found that the forward flow-formed D6ac electron beam weldment heat-treated at 350-450 degrees C and held at this temperature range for 2 h exhibits high mechanical strength, sufficient elongation and a yield strength/ultimate tensile strength ratio of 0.91.