Effect of Post-Weld Treatment on the Microstructure and Mechanical Properties of Austempered FeNiCr Steel Welded Joint

Abstract

This study investigated isothermally treated FeNiCr structural steel welded joints. The base metal contains various phases which are dominated by a mixture of bainite and martensite. Joining this steel can be challenging since it has high carbon equivalent values and high hardness. Shielded metal arc welding (SMAW) with austenitic stainless-steel electrodes is used to avoid cold cracking. After the welding process, the samples were subjected to three various post-weld temperatures: 425°C, 475°C, and 525°C. From the tensile test results, the tensile strength of welded joint shows an increase as the temperatures increase. The highest value is reached for a joint sample which treated at 525°C, with a tensile strength of 680 MPa. Conversely, the highest elongation is obtained by the 425°C post-treated sample, which is 14%. The microstructure in the weld metal (WM) area shows a formation of δ-ferrite, whereas the HAZ and BM areas show the presence of bainite and martensite tempered phases with various plate densities, plate size, and plate shapes depending on its post-treatment temperatures, which then affect the value of the hardness.