Modelling of Nitride Precipitation during Isothermal Heating after Rapidly Cooled from High Temperature in Duplex Stainless Steel

Abstract

Modelling of nitride precipitation during isothermal heating was conducted in duplex stainless steel which was rapidly cooled from high temperature before isothermal heating. Nitride precipitation is frequently harmful for the properties such as toughness or corrosion resistance in duplex stainless steels. The heat affected zone (HAZ) in the vicinity of fusion boundary in weldments tends to have more remarkable nitride precipitation because of rapid cooling from the ferrite phase enriched temperature. It was taken into considered in modelling of nitride precipitation phenomena that the growth of austenite phase from overcooled ferrite phase occurs concurrently in the HAZ in weldment of duplex stainless steel. Because the austenite phase has extremely higher solubility of nitrogen than the ferrite. Employing 25%Cr duplex stainless steels containing the levels of nitrogen of 0.1% and 0.3%, the measurement and observation of nitride precipitation were conducted in the specimens isothermally heated at 873 K to 1 073 K after rapidly cooled from 1 653 K. The model to describe the change of nitride precipitation during isothermal heating considering the effect of growth of austenite phase was proposed and that was confirmed to be good fit to the experimental results.