Tensile and fatigue properties of 17-4 PH stainless steel at high temperatures

The tensile and high-cycle fatigue properties for 17-4 PH* stainless steels in three different conditions were investigated at temperatures ranging from room temperature to 400 T. Results indicated that the yield strength and fatigue strength for the three conditions at a given temperature took the following order: condition H900 > condition A > condition H1150. The yield strength of each condition decreased with increasing temperature except for condition A, which was tested at 400 degreesC with longer hold times, where a precipitation-hardening effect took place. The S-N curves showed that the fatigue strengths of each condition in the short-life regime were decreased with an increase in temperature. In the long-life regime, the fatigue strengths of condition A at 400 T were greater than those at lower temperatures as a result of an in-sitit precipitation-hardening effect. The fatigue strengths of condition H900 in the long life regime at 300 T were superior to those at lower temperatures, due to the mechanisms of surface oxidation and thermal activation of dislocations. Fractography observations indicated that a shift of fatigue fracture from surface to internal crack initiation occurred at higher temperatures (300 T and 400 T) with long fatigue lives.