2013 年 54 巻 9 号 p. 1612-1618
The cyclic response of the SUS316L stainless steel with the nanostructure induced by profuse twinning during equal channel angular pressing (ECAP) at 423 K was investigated with the focus on the shape of the hysteresis loops and their evolution with cycling. The SUS316L steel with the nanostructured twins showed a very high stress amplitude if compared to their conventional counterparts. However, unlike the as-quenched specimens, the ECAPed SUS316L steel revealed considerable cyclic softening at plastic strain amplitudes above 2 × 10−4. Besides, the ECAPed specimens showed characteristic stress asymmetry behavior during fatigue. At the initial stages of the fatigue tests, a tensile peak stress of the hysteresis loop was higher than a compressive one. Then, the tensile peak stresses gradually decreased with increasing cycles and finally became lower than the compressive peak stress under plastic strain amplitudes higher than 2 × 10−4. Since no stress asymmetry was detected for the as-quenched sample, the observed stress asymmetry behavior was attributed to the specific asymmetric response of the directionally sheared microstructure created during ECAP.
