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°C. 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°C 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°C were greater than those at lower temperatures as a result of an in-situ precipitation-hardening effect. The fatigue strengths of condition H900 in the long life regime at 300°C 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°C and 400°C) with long fatigue lives.