Effect of the Addition of Nickel Powder and Post Weld Heat Treatment on the Metallurgical and Mechanical Properties of the Welded UNS S32304 Duplex Stainless Steel

Efeito da Adição de Pó de Níquel e do Tratamento Pós Soldagem nas Propriedades Metalúrgicas do Aço Inoxidável Duplex UNS S32304 Soldado

Abstract

In this research, the effect of the addition of nickel powder and the application of a post weld heat treatment (PWHT) on the welding properties of the UNS S32304 lean duplex stainless steel were investigated in order to improve the microstructure and mechanical properties. Nickel powder was directly poured inside the joint gap and mixed with the filler metal during the Gas Tungsten Arc Welding (GTAW) process; moreover, the solution heat treatment was performed at 1100 °C for 10 min. The joints were characterized by optical microscopy (OM) and the evolution of the phase percentages in the different zones was studied by means of the image analysis technique. Tensile and hardness tests were carried out on the joints in order to evaluate the improvement of the mechanical properties. The results showed that both the addition of nickel powder during the welding process and the post weld heat treatment made it possible to improve the mechanical properties of the weld joints. PWHT had the best effect in restoring the equal percentage of ferrite and austenite compared to the addition of nickel powder.

Key-words
Duplex stainless steel; GTAW process; Nickel powder; PWHT; Microstructure