High temperature fatigue behaviors of a cast ferritic stainless steel

This work investigated the high temperature low cycle fatigue (LCF) behavior of ACI HB20-type, cast ferritic stainless steel. In addition to the preliminary results from tension test, isothermal strain controlled fatigue tests were carried out at 600 °C and 800 °C. The total strain amplitudes applied to the samples were from ±0.25% to ±0.65% with a strain rate of 10−3/s. The fatigue lifetime curves at each temperature were obtained based on Basquin and Coffin–Manson equations. Also, these temperature dependent plots were re-constructed into a general superposition curve and compared to other heat resistant stainless steels. Additionally, microstructure and fractured surface after LCF test were analyzed using a scanning electron microscopy suggesting that the crack initiated at the grain boundary of the surface and propagated intergranularly as well as transgranularly. This is attributed by the formation of Cr and Nb carbide along the grain boundaries.