Effect of Co on the strengthening mechanisms of the creep-resistant 9% Cr-2%W-MoVNb steel

The alloying by 3 wt.% Co increases the tensile strength of the P92-type steel at elevated temperatures. The increments in the yield strength are 20%, 11% and 12% at testing temperatures of 500 °C, 600 °C and 650 °C, respectively, as compared with the Co-free P92-type steel. Cobalt strongly affects the strengthening due to the martensitic laths and dislocations regarding the lath growth and dislocation motion. The increases in the strengthening due the martensitic laths and the dislocations comprise 22, 43, 33 and 31 MPa at 20 °C, 500 °C, 600 °C and 650 °C, respectively. Reduction in initially higher dislocation density in the Co-containing steel occurs significantly less than that of the P92 steel at tensile tests at elevated temperatures. On the other hand, the influence of Co on interaction of free lattice dislocations with secondary particles or solid solution is negligible at tensile tests. The increments in the strengthening due to particles and solid solution are about 9% and 5%, respectively, at all tensile tests.