Role of dynamic strain aging in the tensile property, cyclic deformation and fatigue behavior of Z2CND18.12N stainless steel between 293 K and 723 K

Tensile properties and cyclic stress–strain response of Z2CND18.12N austenitic stainless steel were investigated at the strain rate of 1×10−3/s in the temperature range between 293 K and 723 K. Low cycle fatigue tests were also carried out at the strain rate of 6×10−3/s at 293 K and 623 K. SEM and TEM analyses were performed on the fatigue specimens. Tensile strength and ductility were found to reduce drastically with the temperature increasing from 293 K to 423 K but almost remained on the same level in the range between 523 K and 723 K. Serrations occurred during the stress approaching the ultimate tensile strength at 623 K and 723 K. The cyclic stress responses at temperatures ranging from 293 K to 623 K were characterized by a rapid initial hardening to the maximum stress, followed by gradual softening, whereas at 723 K continuous cyclic hardening was present. The maximum cyclic hardening ratio, defined as the maximum peak stress divided by the initial peak stress, increased with increasing temperature in the present temperature range. Phenomenological friction and back stresses were derived from an analysis of hysteresis loop shapes using the Cottrell scheme. The results indicated that the increase of back stress was mainly responsible for the cyclic hardening. Fatigue life decreased with increasing strain amplitude at both 293 K and 623 K. Transgranular fracture failure mode was observed at both temperatures. TEM observations revealed that the dislocation structure changed from the cellular structure at 293 K to the planar slip band at 623 K. Dynamic strain aging has been believed to play a significant role in tensile properties, cyclic deformation and fatigue behavior of the material.