Improvement of High Temperature Strength of Austenitic Stainless Steel by Additions of Silicon and Nitrogen

Abstract

The effect of additions of Si, N and C on the creep rupture strength of Ni-Cr austenitic steel was studied, and the effect of heat treatment on the creep strength of 2%Si-13%Ni-24%Cr-0.25%N steel was also studied.
The creep mpture strength at 1000°C depends on Si/N and the maximum value is obtained at Si/N≈10. Strengthening by additions of Si and N may be attributed mainly to the retardation of the Cr-nitride precipitation by addition of Si. Rupture elongation increases with Si content. Creep mpture strength at 1000°C increases with C content up to 0.10%, above which the strength decreases at longer time.
Based on these data, 0.1%C-2%Si-13%Ni-24%Cr-0.25%N austenitic steel is designed for radiant tube use. In this steel further improvement of the strength is obtained by high temperature (1200-1250°C) solution treatment. In this condition, the creep rupture strength of this steel is included in the data band of HK40 surveyed by Nishino. The creep rupture strength at 1000°C decreases with ageing or cold worklng. Welded tube of this steel is put to the test for radiant tube, and it was found that this steel has excellent perfbrmance and durability.