Effects of Small Amount of Vanadium and Niobium on Microstructure and Creep Rupture Strength of 12 Percent Chromium Heat Resisting Steel

Abstract

Effects of small addition of vanadium and niobium were investigated in order to improve the creep rupture strength of 12% Cr heat resisting steel. The results are as follows.
1) The creep rupture strength of 12% Cr heat resisting steel is increased by the addition of small amounts of vanadium and niobium. Additions of vanadium and niobium result in precipitation hardening. Especially, in the case of combined addition of vanadium and niobium, the creep rupture strength is higher than that in the case of individual addition of vanadium or niobium. In the case of individual addition, the creep rupture strength of steel containing niobium is higher than that of steel containing vanadium up to 600°C.
2) It is observed in an electron microscope that coalescence of precipitated carbide particles are retarded by additions of vanadium and niobium to the steel.