The strengthening mechanism of 9Cr-1.5Mo-1Co and 9Cr-3W-3Co heat resistant steel was studied by tensile test and microstructure analysis. At the same temperature, the yield strength of 9Cr-3W-3Co heat-resistant steel is higher than that of 9Cr-1.5Mo-1Co heat-resistant steel. Microstructure analysis proved that the strength of 9Cr-1.5Mo-1Co and 9Cr-3W-3Co heat-resistant steel is affected by grain boundary, dislocation, precipitation, and solid solution atoms. The excellent high temperature mechanical properties of 9Cr-3W-3Co heat-resistant steel are mainly due to the solution strengthening caused by Co and W atoms and the high-density dislocations distributed in the matrix; however, 9Cr-1.5Mo-1Co heat-resistant steel is mainly due to the martensitic lath and precipitation strengthening.
Keywords: cast steel; heat-resistant steel; microalloying; strengthening mechanism.