High temperature bending fatigue behavior of stainless steels for automotive exhaust

Continually increasing working temperatures and a growing need for greater efficiency and reliability of automotive exhaust system require immediate investigation into the high temperature fatigue properties of heat resisting stainless steels. In this study, evaluation method of high temperature bending fatigue life has been established and S–N curves for ferritic stainless steels, such as 409L, 436L and 429EM STS, produced by POSCO have been evaluated at the temperatures of 600 and 800 °C, which are typical temperatures of exhaust system exposed during operation of a vehicle. Endurance limit of 429EM was found to be higher than the other two stainless steels and significantly reduced with increasing temperature, from 150 MPa at 600 °C to 65 MPa at 800 °C. Thickness effect on the fatigue life has also been investigated by varying the thickness of specimen and was found insensitive within the thickness range from 1 to 2 mm.