Effect of heat treatment on microstructure and hardness changes in weld steel precipitation of hardening 17-4PH

In this study the effects of heat treatment after and before welding on the microstructure and mechanical properties of 17-4 PH steel with ER347 beads was investigated. In this study before welding the samples were dissolved at 1038°C. welding the samples was conducted under these conditions: without pre-heating, flat and butt-weld positions with tungsten arc welding . after dissolving at 1038°C the sheets were prepared as follow : 1- welding + aging at 566°C, 2- aging at 620°C + welding. The microstructure and hardness of the samples were investigated by optical and Scanning Electron Microscope (SEM) system and the sclerometer was studied. The results indicate that the microstructure of the welding region before heat treatment consists mainly of a layer of not tempered martensite, with delta ferrite fibers, the constructed ferrite is composed mainly of intercell ferrite and vermicular delta ferrite.