Austenitic stainless steel

Abstract

An austenitic stainless steel, which comprises by mass %, C: 0.04 to 0.18%, Si≦1.5%, Mn≦2.0%, Ni: 6 to 30%, Cr: 15 to 30%, N: 0.03 to 0.35%, sol. Al≦0.03% and further contains one or more elements selected from Nb≦1.0%, V≦0.5% and Ti≦0.5%, with the balance being Fe and impurities, and among the impurities P≦0.04%, S≦0.03%, Sn≦0.1%, As≦0.01%, Zn≦0.01%, Pb≦0.01% and Sb≦0.01%, and satisfy the conditions P1=S+{(P+Sn) / 2}+{(As+Zn+Pb+Sb) / 5}≦0.06 and 0.2≦P2=Nb+2(V+Ti)≦1.7−10×P1 has high strength and excellent resistance to cracking due to grain boundary embrittlement in the welded portion during the use at high temperatures. Therefore, the said steel can be suitably used as materials for constructing machines and equipment, such as power plant boilers, which are to be used at high temperatures for a long period of time.

Description

TECHNICAL FIELD[0001]The present invention relates to an austenitic stainless steel. More particularly, the present invention relates to a high strength austenitic stainless heat resistant steel which is to be used in constructing high temperature machines and equipment, such as power plant boilers, and is excellent in resistance to cracking at weld heat affected zone due to grain boundary embrittlement during use at high temperatures.BACKGROUND ART[0002]In recent years, the operation conditions for power plant boilers and the like have become higher temperature and higher pressure ones on a worldwide scale in consideration of environmental deterioration. Therefore, these austenitic stainless heat resistant steels which are to be used as materials for superheater tubes and reheater tubes are required to have increased high temperature strength.[0003]In such a technological background, various austenitic stainless steels have been disclosed.[0004]For example, the Patent Document 1 di...

AI Technical Summary

Benefits of technology

The present invention aims to provide an austenitic stainless steel with excellent resistance to cracking in the welded portion after a long period of use at high temperatures. The invention proposes a solution to prevent cracking by restricting the contents of grain boundary-embrittling elements, specifically P, S, Sn, Sb, Pb, Zn and As, within specific ranges. The invention also discusses the microstructure and mechanisms of cracking in the welded portion after a long period of use at high temperatures and proposes measures to prevent such cracking.

Problems solved by technology

While these austenitic stainless heat resistant steels are generally used at high temperatures after welding fabrication, they encounter the problem of an occurrence of cracking in the weld heat affected zone (hereinafter referred to as “HAZ”) after a long period of use at high temperatures.