Effects of Nickel and Nitrogen on Austenite Phase Growth in Rapid Cooled Microstructure from High Temperature in Duplex Stainless Steel

Abstract

The growth of austenite phase from overcooled ferrite phase in duplex stainless steel was investigated to clarify the quantitative effects of nickel and nitrogen on that in isothermal heating process. The ratio of ferrite and austenite phase is very important factor to obtain the maximum performance such as toughness and corrosion resistance of the steels. However, the fraction of austenite phase in heat affected zone (HAZ) in weldments can be changed in the portion closed to fusion boundary during welding process. The measurement of austenite phase fraction was conducted experimentally in the specimens after rapid cooled from 1 653 K and isothermally heated at various temperature, employing the 25%Cr or 22%Cr duplex stainless steels containing various level of nickel and nitrogen. Applying those data obtained to the model proposed where the growth rate of austenite phase is determined as the function of isothermal temperature, the effects of nickel and nitrogen on the growth behavior of austenite phase was clarified by determining the parameters for each steel in that function. The validity of this manner was clarified by confirming the applicability of the model proposed to the experimental data obtained by another authors.