Study Of Experiment And Simulation On Deformation Heterogeneity In Microregion Of 316lN Stainless Steel With Coarse Grains

In the hot forming of 316 LN stainless steel for nuclear power main pipeline,millimeter-sized coarse grains are often found,which seriously damages the mechanical properties of the material.316 LN stainless steel is an austenitic single-phase steel.Its grains cannot be refined by heat treatment,but can only be crushed by deformation-induced recrystallization.Compared with fine grains,the deformation of coarse grains is more difficult.How to refine coarse grains is a problem worthy of attention in the field of hot working.In this paper,the mechanism of grain breakage and recrystallization induced by inhomogeneous deformation of coarse grains in micro-region is explored through experiment and simulation.Firstly,the influence of coarse grains on the deformation inhomogeneity of micro-region was qualitatively analyzed by compression test at room temperature and electron backscatter diffraction(EBSD).It was found that with the increase of deformation,the soft-oriented coarse grains would rotate and the dislocation slip in the local region of the grains would form a high dislocation density area which induced recrystallization.Then,the representative surface unit of twodimensional mixed crystal structure is created by EBSD data,and the material parameters in the phenomenological rate-dependent constitutive equation are obtained by fitting the flow stress curve which is gained at room temperature.The full-field CP simulations were performed to simuate the strain field with the global deformation of 6%.Then,the digital image correlation method(DIC)is used to simulate the strain field.The results of strain distribution in the micro-region measured by experiments and simulation are compared,and the correctness of the model is verified.According to the simulation results of CPFEM,the stress-strain nephogram after large deformation is acquired.The possibility of producing slip band and sub-structure in coarse grains is analyzed.The results show that slip band may occur in coarse grains,but sub-structure is difficult to appear.In order to clarify the triggering mechanism of inhomogeneous deformation distribution on RX,heating and static recrystallization experiments were carried out on deformed specimens.The results show that when the deformation is small,the coarse grains are still large after recrystallization,but when the deformation is large,the same fine grains are obtained from the original coarse grains and fine grains after being recrystallized,besides,the traces of the original coarse grains cannot be observed any more.This indicates that the recrystallization of coarse grains under large deformation may nucleate along the slip band with high dislocation density in addition to the nucleation at grain boundary.