Dissolution of δ-ferrite and its effect on mechanical properties of P92 steel welds

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2020-10, Vol.796, p.139370, Article 139370
• Main Authors: Saini, Nitin, Mulik, Rahul S., Mahapatra, Manas Mohan, Kannan, Rangasayee, Sharma, Nitin Kumar, Li, Leijun
• Format: Article
• Language: English
• Subjects: Charpy toughness; Chromium; Delta ferrite; Dissolution; Gas tungsten arc welding; Heat resistant steels; Heat treating; High strength steels; Mathematical analysis; Mechanical properties; Microhardness; Morphology; Normalizing (heat treatment); Post-weld heat treatment; PWHT; PWNT; Solidification; Tempering; Welded joints; δ-ferrite
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.139370

This paper reports on the dissolution of δ-ferrite in the weld fusion zone using post-weld normalizing and tempering (PWNT) and its effect on mechanical properties. The autogenous gas tungsten arc welding (GTAW) was used to prepare double-sided welded joints of P92 steel. After welding, post-weld heat treatment (PWHT) at 760 °C for 2 h and post-weld normalizing at 1050 °C for 1 h followed by tempering at 760 °C for 2 h were performed. The morphology, composition, structure, and hardness of δ-ferrite are verified. The effect of PWHT and PWNT on mechanical properties is also observed. In as-welded and PWHT conditions, the retention of δ-ferrite was observed while the dissolution of δ-ferrite was confirmed after PWNT. In the PWNT condition, uniform microhardness across the welded joint, increased ductility, and increased Charpy toughness of weld fusion zone (almost equal to as received material) were achieved. Dissolution kinetics of δ-ferrite is quantified using Thermo-Calc for Scheil's solidification calculation and DICTRA for calculating diffusion coefficients of Cr and W at 1050 °C in austenite.