Uniaxial ratcheting behavior and microstructure evolution of 316H stainless steel under the random cyclic loads.

In this study, the Computational Fluid Dynamics (CFD)-Finite Element Method (CFD-FEM) were used to simulate the transient stress response of the structure surface under thermal striping environment, and a uniaxial random cyclic loading (RCL) method was used to reveal the mechanical properties and initial microstructure evolution of 316H austenitic stainless steel (SS) under random stress induced by thermal striping. The experimental results showed that 316H exhibited a lower saturation ratcheting strain rate at 334.44 MPa, along with stronger cyclic hardening effects and resistance to plastic accumulation at loading rate of 100 Hz. Random loading tests with different cycles were performed at σ peak = 334.44 MPa and f R C L = 100 Hz , and ratcheted specimens were characterized to investigate the effect of the micro-mechanism on cyclic softening/hardening. The geometrically necessary dislocation (GND) density increases and then decreases with cyclic loading, which is mainly attributed to the deformation twin (DT) and multi-dislocation slip mechanisms. The deformation mechanism during the ratcheting cycle from 1000 to 3000 cycles is mainly dominated by the twinning reduction, where the dislocation migration accelerated the transformation from dislocation walls to subgrain boundaries; the twinning increase dominates from 3000 to 9000 cycles, where the subgrain boundary grew into boundaries with high angle misorientations. • Significant tensile ratchet deformation occurred when the peak stress was >274.14 MPa. • The cyclic hardening and suppressed ratcheting strain were observed due to asymmetric peak and valley loading. • The critical cycles of ratcheting strain growth rate decrease with the loading frequency. • Dislocations sunk by grain boundaries under random cyclic loading. • Twinning decreases at low cycles and increases at high cycles during RCL deformation. [ABSTRACT FROM AUTHOR]