Structural Change Occurred by Furnace Cooling and Its Effect on Creep Rupture Properties of 21-12N Steel

Abstract

It was found that the grain boundary serration could be produced when commercial 21-12N steel was furnace-cooled from various solution temperatures.
In this study, the condition required to serrate the grain boundaries in high Cr-Ni steel was determined and the effect of the furnace cooling on the creep rupture roperties of 21-12N steel was investigated.
In order to serrate the grain boupdaries, high Cr-Ni steel, in which C or N more than 0.2% or 0.3% was contained respectively, had to be transferred from solution temperatures to the higher temperature region around 900 and then held for a certain time at the same region in which the nucleation rate of precipitates was not so fast, but both nucleation growth and grain boundary migration were ready to occur, without passing through the lower temperature region around 700°C in which precipitates were ready to nucleate.
Smooth and notched creep rupture properties at 600°C of 21-12N steel were improved remakably by the furnace cooling, while at 700°C the effect of the furnace cooling was decreased gradually as the rupture life increased.