Room- and service-temperature tensile properties of repeatedly welded austenitic stainless steel by Gleeble simulation of heat-affected zone

Abstract

The effects of repeated welding on the microstructure and tensile properties of the heat-affected zone (HAZ) of AISI 304N austenitic stainless steel at room and service temperatures were investigated using a Gleeble welding simulator. Thermal cycle parameters were obtained by in situ measurements of the HAZ of seven sequential weld beads. By thermal cycling in the Gleeble simulator, specimens were prepared to simulate the HAZs of steels in the as-welded condition and after one to five repeated welding processes, designated as AW and RW1–RW5, respectively. The HAZ microstructures were characterised and tensile tests were conducted at room temperature and the equipment service temperature of 260 °C. The repeatedly welded specimens showed microstructures of austenitic matrices with δ-ferrite inclusions. The average austenite grain size was 41.4–47.3 μm and the δ-ferrite content was 0.69–3.13 vol%. RW2 exhibited the maximum percentages of 31.8% and 15.9% high-angle boundary (HAB) and coincidence site lattice, respectively, while RW4 exhibited the minimum values of 22.3% and 9.0%, respectively. At room temperature, the ultimate tensile strength (UTS) and yield strength (YS) were 525–670 MPa and 190–245 MPa, respectively; at 260 °C, they were 460–475 MPa and 200–215 MPa, respectively. The room-temperature UTS and YS mainly depended on the contents of δ-ferrite and HABs. As the δ-ferrite content decreased and the frequency of HABs increased, the UTS and YS were increased. However, the boundary activation energy and dislocation resistance decreased at the service temperature, where the effects of the δ-ferrite and HAB contents on the UTS and YS were weaker.