Effect of precipitation of σ-phase and N addition on the mechanical properties in 25Cr-7Ni-4Mo-2W super duplex stainless steel

Abstract

This study was carried out to investigate the effects of precipitation of σ phase and N addition and the change of volume fraction on the mechanical properties in 25Cr-7Ni-4Mo-2W super duplex stainless steel. The results obtained from this study are as follows: With increasing the annealing temperature, the volume fraction of austenite increased while volume fraction of ferrite decreased. Volume fraction of austenite was found to be increased by N addition. Tensile strength decreased and elongation increased due to increasing the volume fraction of austenite by increasing annealing temperature. In the case of specimens with N addition, tensile strength and elongation showed high values, σ phase was formed at ferrite phase and interface of ferrite and austenite. More precipitation of σ phase was stimulated by N addition. With increasing volume fraction of precipitated σ phase, tensile strength was increased, while elongation and impact value decreased. In the case of σ phase precipitated specimen (with N addition), tensile strength, elongation, hardness and impact values showed higher values than those without N addition. It was also found that impact value rapidly decreases in early stage of aging. © 2005 The Japan Institute of Metals.