Effect of the Compositional Balance of Mo and W on Long-term Creep Strength of 10%Cr-3%Co Ferritic Steels

Effect of the compositional balance of Mo and W on long-term creep strength of 10%Cr-3%Co steels was investigated at temperature of 600 and 650°C under stress of 200 and 120 MPa respectively. The creep rupture strength in both conditions took a maximum point in the parameter of 0.5W/(Mo+0.5W). This phenomenon may occur through different solid solution hardening of Mo and W due to differing behaviour of the Laves phase precipitation, suggesting that it depends on the compositional balance of Mo and W. It is also found that dispersion hardening and dislocation hardening after long-term creep are unaffected by the difference between the compositional balance of Mo and W. In spite of the difference between the compositional balance of Mo and W, the long-term creep strength of the steels can be described as a function of the solute mole fraction, C, times the second power of the size-misfit parameter, εb2. This is suggested that the long-term creep strength of the steels is controlled principally by solid solution hardening, in addition to dispersion hardening and dislocation hardening.