Stress relief heat treatment in duplex stainless steels

Abstract

The production of massive castings (over two tonnes) in duplex stainless steel with thicknesses that exceed 120 mm presents a major challenge for the foundry industry. The purpose of this work is to study the behaviour of two duplex stainless steels in impact tests after solution annealing with water quenching and stress relief at 350°C for 4 h and at 550°C for 2 h. Due to the presence of nitrogen, the CD4MCuN stainless steel exhibits a more balanced microstructure with similar ferrite and austenite contents, yielding a higher energy-absorbing capacity in impact tests. The fracture surfaces are fibrous structures that are typical of high toughness materials, while the CD4MCu steel fracture surface exhibits cleavage facets that are typical of low toughness materials. Stress relief heat treatments reduced the impact toughness of the CD4MCu alloy, but did not affect the CD4MCuN alloy.