Abstract
It is known that 12% Cr heat resisting steel is one of the most economical heat resisting steels. It is, how-ever, inferior to austenitic heat resisting steels in the creep rupture strength above 600°C. So, the effects of Mo and W were investigated in order to improve the creep rupture strength of 12% Cr heat resisting steel containing V, Nb, and B.
(1) The creep rupture strength of 12% Cr heat resisting steel is increased by the additions of Mo and W. Additions of Mo and W result in solid solution strengthening as well as precipitation hardening.
(2) In the case of a single addition, optimum amount of Mo is about 1.5% and that of W is about 3.0%. Whereas in the case of a combined addition, optimum amounts of M and W are both about 1.0%.
(3) It is observed in an electron microscope that coalescence of precipitated carbide perticle are retarded by the additions of Mo and W to the steel.
