Ultrasonic fatigue of AISI 4140 at elevated temperaturesThursday (28.05.2020) 11:30 - 11:50
In this study, the fatigue life of cast steel AISI 4140 in two different heat treatment states was investigated at room temperature, 473 K and 773 K in the range of VHCF up to 10^9 cycles. The detrimental effect of the cast defects on the fatigue strength and the influence of temperature as well as hardness of the steel matrix determine the fatigue life. Fracture surfaces were analysed regarding crack initiating defects and discussed with fatigue life data. The SN-curves obtained at room temperature and at 473 K show a large scatter. However, the SN-curve at 773 K exhibits a larger slope and a surprisingly small scatter. Thus, fatigue lives of the specimens tested at 773 K were described on basis of a crack growth model. It is shown, that the fatigue behaviour of the cast steel AISI 4140 changes from 473 K to 773 K and no fatigue limit was observed at high temperature in the range of VHCF.