Abstract
The fatigue strength at room temperature and microstructure of the type 316 austenitic stainless steel with and without various thermo-mechanical treatments were investigated and the test results by a ultrasonic fatigue testing machine were compared with that by a conventional tension-compression fatigue testing machine.
The 106 cycle fatigue strength of type 316 steel increased about 30% by the tensile cold work of 30%, and moreover by the aging treatment of 30hr at 700°C after 20% cold work about a 50% increase of 106 cycle fatigue strength was obined comparing with that of the solution treated steel. These fotigue strengths, however, are a little smaller than that obtained by the treatment, 20% cold working followed by aging of 24hr at 480°C and 216hr at 700°C, which was proposed by Garofalo.
Based on the results of the microstructural survey, it was suggested that the high dislocation density and fine and homogeneous distribution of precipitated M23C6 carbide contribute to the strengthening of the thermo-mechanical treated steels.
The S-N curves both by ultrasonic and magnetic fatigue testing machines showed an almost similar tendency. Therefore, the advantage of ultrasonic fatigue testing machine in time-saving of the testing of type 316 steel was confirmed.
