Detection of low cycle fatigue in type 316 stainless steel using HTS-SQUID

A portable RF HTS SQUID-based susceptometer was applied to the measurement of fatigue behavior for type 316L(N) stainless steel containing 0.04% to 0.15% nitrogen content. Strain-controlled low cycle fatigue (LCF) tests were conducted at RT and 600 degreesC in air an atmosphere, and the magnetic moments were measured after the fatigue test using HTS SQUID. The magnetic moment of an as-received sample is higher than that of a fatigued sample in all the temperature ranges irrespective of the nitrogen content. The fatigue life decreased with an increasing test temperature up to 500 degreesC, but increased at 600 degreesC. The change of magnetic moments by LCF test is attributed to the stress induced micro defects.