Effects of Post Weld Ageing Heat Treatments on the Microstructure of 17-4PH GTA Welded Joints

Abstract

The mechanical and metallurgical properties of the 630 (17-4PH) precipitation hardening stainless steel is greatly influenced by the type of applied heat treatments cycles. In order to achieve the homogenous microstructure in the weld metal and eliminate the HAZ due to producing the weak mechanical strength, and producing similar microstructures and mechanical strength in both weld and base metal, the study was conducted to find an optimum pre and post heat treatments before and after welding. The 2.2mm thick and 48mm tube diameter made of 630 stainless steel were welded under various operational parameters. The samples were subjected to pre weld solution treatment and post weld aging heat treatment. To reveal the microstructures of the welds, the optical and scanning electron microscopy of the welds carried out. The study shows that the direct ageing treatment at 6200C after welding can give rise to the best heat treatment to produce, the uniformity in the grain size, mechanical strength and hardness, between the base metal and the weld metal.