Abstract
In order to develop the high strength heat resisting steel served at temperatures above 600°C, the effectsof C and Nb contents and heat treatment on creep rupture strength of 18Cr-12Ni-3Mo austenitic steelcontaining 0.15%N were investigated.
Creep rupture strength was given as a function of Nb/(C +N)(atomic per cent ratio) irrespective of Cand Nb contents and reached maximum at Nb/(C+N) =0.3-0.5. Moreover, creep rupture strengthincreased with increasing solution treatment temperature, which was due to the solid solution hardeningof Nb (C, N) and the grain growth of austenite.
As results, the steel with nominal composition of C0.1, Si0.8, Mn1.5, Cr18, Ni12, Mo3, Nb0.7, N0.15, B 0.02% was developed. 10000 hr creep rupture strength of this steel was 20kg/mm2 at 650°C, 13-5 kg/mm2 at 700°C and 9.8 kg/mm2 at 750°C. It was concluded that this favourable creep rupture strength for long time up to 750°C is mainly due to the excellent structural stability.
