Study On Hot Working Process Of Austenitic Stainless Steel Based On Dynamic Recrystallization

Mechanical thermal processing is an important method of metal processing,which can effectively improve the mechanical properties by changing the internal structure of the material.Therefore,the research on the internal microstructure evolution behavior during mechanical thermal processing has important practical significance.The microstructure evolution process during the mechanical thermal processing of 316 L stainless steel and 2205 duplex stainless steel are studied by Gleeble thermal simulation test machine.The crystal plasticity finite element method is used to simulate the micro deformation characteristics during the mechanical thermal processing of duplex stainless steel.Optical metallographic microscopy(OM),electron backscattered diffraction(EBSD),transmission electron microscopy(TEM),and scanning transmission electron microscopy(STEM)are used to characterize detailed deformation microstructure of two materials.The main research content and conclusions of the paper are as follows:(1)The stress-strain curve of 316 L austenitic stainless steel at 950?~1250?was obtained by a monotonous compression experiment with different deformation parameters on a Gleeble thermal simulation test machine.The activation energy of316 L stainless steel is determined by the classical Zener-Hollomon parameter equation.The constitutive relation of 316 L stainless steel is established.The experimental samples under different deformation conditions were characterized and analyzed,and the effects of different temperatures and strain rates on the thermal deformation behavior of 316 L stainless steel were described.(2)The coarse-grained 316 L stainless steel is used as the experimental material of the Gleeble thermal simulation test machine for monotonous compression and complex compression with a transient strain rate.Various characterization methods such as electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM)are used to characterize detailed microstructure of deformed samples.For coarse-grain austenite with low stacking fault energy,the continuous dynamic recrystallization(CDRX)mechanism is the main mechanism of dynamic recrystallization.This phenomenon has been found in the study of monotonous compression test.The sub-crystals formed at the initial stage of deformation will promote the development of dynamic recrystallization in the subsequent deformation,which was found in the complex compression experiment with a transient strain rate.(3)In order to study the internal deformation of the microstructures in the work hardening stage of the duplex stainless steel during the hot working process,a crystal plasticity finite element(CPFEM)model based on real microstructure data coupled with the representative volume element(RVE)method was established.The simulation results show that the compression deformation of the dual-phase polycrystalline structure is extremely inhomogeneous on the mesoscopic scale.The distribution of stress and strain fields in the deformed structure is uneven and mostly concentrated at the phase boundaries,which is caused by the different mechanical properties of austenite and ferrite.The simulated stress concentration position,strain band distribution and overall stress-strain curve are basically consistent with the results obtained from the thermal compression experiment,which verifies the validity of the RVE-CPFEM model and the accuracy of the deformation structure simulation.