Effect of Individual Addition of Alloying Element on the Creep-Rupture Strength and Microstructure of 12% Cr Steel

Abstract

High pressure and temperature steam condition of recent steam turbine demands development of 12%Cr steel having superior elevated temperature strength. So, the effects of individual addition of alloying element such as Mo, W, Ti, V and Nb have been investigated in order to improve the elevated temperature strength of 12%Cr steel.

The elevated temperature strength of 12%Cr steel is increased by individual addition of alloying element such as Mo, W, Ti, V and Nb. Additions of Mo or W results in solid solution strengthening as well as precipitation hardening, whereas those of Ti, V or Nb results in precipitation hardening. The strengthening effect can be explained by the difference in atomic volume between Fe and the alloying elements. It is observed under transmission electron microscope that the dislocation density becomes higher, as the difference in atomic volume is larger. As a result, the creep rupture strength of the steel is increased.