Effect of Small Additions of Ti and Nb on the Creep-Rupture Strength of High-Alloy Austenitic Stainless Steels

Improvement of the creep-rupture strength of 18-8 stainless steel (Type 304) by additions of small amounts of Ti and Nb has previously been reported. Such effect of additions of Ti and Nb on the creep-rupture strength of high-alloy austenitic stainless steels such as 22Cr-12Ni or 25 Cr-20Ni has been studied. As a result, it was found that the combined additions of small amounts of Ti and Nb to high-alloy austenitic steels are also effective for improving the creep-rupture strength just like as the case of 18-8 austenitic steel. Further effects of additions of Ti and Nb were found to be as follows:(1) the shape and distribution of precipitated carbides change, (2) the carbide particles precipitate finely and are evenly dispersed. It is concluded that the improvement of creep-rupture strength is considered to be due to the improved dispersion effect of these fine carbide particles.