Influence of Microstructural Changes on Impact Toughness of Weldment and Base Metal of Duplex Stainless Steel AISI 2205 for Low Temperature Applications

Abstract

Austenite (γ) reformation and microstructural changes are the major anxieties in duplex stainless steel welding and aging process. Insufficient stabilization of austenite phases and intermetallic formations due to unfavourable thermal cycle leads to drastic reduction in the ductility and toughness of duplex stainless steel in particularly at low temperature. In this work, an attempt has been made to analyze the microstructure in the DSS weld, heat affected zone and base metal with respect to their impact toughness. DSS weld joints were fabricated using gas tungsten arc welding process with controlled welding parameters. Ferrite austenite ratio in the weld zone, heat affected zone and base metal was assessed by quantitative metallographic image analysis. The impact test results were correlated with the fractured surface and the microstructure of the tested specimens. The effect of heat treatment on the microstructural changes in the weld and base metal were also investigated with respect to impact toughness. Austenite phases were nucleated in the high temperature heat affected zone during heat treatment of weldment at 1050°C for 1 hour and it leads to enhancement in the impact toughness of the DSS weldment. But, drastic reduction in the impact toughness was observed in the base metal after heat treatment at 850°C and 1050°C due to the formation of sigma phase at 850°C and the coarser ferrite and austenite grains and partially dissolved sigma phase in the microstructure of 1050°C heat treated samples.