Effect of solute atoms on thermal fatigue properties in ferritic stainless steels

The hardening ability of some substitutional solute atoms was investigated and compared. It was theoretically shown that solute atoms have the effect to enhance the necking resistance during creep deformation at high temperatures and can improve the thermal fatigue property of the steels. Molybdenum which is known to have large solid solution hardening ability improves the thermal fatigue property by the solid solution hardening itself, plus the enhanced necking resistance through increase in strain rate exponent. Aluminum which is known to improve the oxidation resistance of the ferritic stainless steels has a sufficient solid solution hardening ability. Thermal fatigue life of the steel was improved by a small amount of Al addition. It can be ascribed to the solid solution hardening ability of Al plus the enhanced necking resistance through increase in strain rate exponent due to Al addition. The addition of the appropriate amount of Si would make the effect of solute Al more efficient by improving the oxidation resistance of the steel.