Difference in Susceptibility to 475°C Embrittlement of Duplex Stainless Steel Base Metal and Weld Metal

Abstract

Duplex and super duplex stainless steels are susceptible to thermal aging embrittlement, referred to as 475°C (885°F) embrittlement. The object of this study is to understand the difference in susceptibility to 475°C (885°F) embrittlement of the base metal and the weld metal of these steels. Isothermal aging heat treatment at 300–450 °C (570–840°F) up to 1,000 hours was performed on 22% Cr duplex stainless steel: UNS S32205 and 25% Cr super duplex stainless steel: UNS S32750 and S32760 and these weld metals made using their matching SMAW electrodes or GTAW rods. After heat treatment, the embrittlement behavior was evaluated by Charpy impact test and Vickers hardness test. The results revealed the time-temperature embrittlement curves of the weld metals were displaced to a significantly shorter period of time and extended to lower temperatures compared to those of the corresponding base metals. More importantly, these results suggested that the maximum design temperature limit on these steels currently specified in the ASME Pressure Piping Codes and Boiler and Pressure Vessel Code is not always sufficient to avoid the risk of 475°C (885°F) embrittlement in their welded components.