Study On The Effect Of Phase Reversion Process On The Microstructure And Properties Of 301 Austenitic Stainless Steel Strip

Austenitic stainless steel has excellent corrosion resistance,ductility,biocompatibility and good processing performance.It is widely used in many fields such as construction,medical treatment,transportation,electronic products,military industry and aerospace.However,its yield strength and tensile strength are low.Although the conventional strengthening method improves the strength,it also deteriorates the plasticity of austenitic stainless steel and limits the development prospect of austenitic stainless steel.With the development of economy,in order to ensure the structural strength of the heavy austenitic stainless steel plate has been unable to adapt to China ’s carbon peak,carbon neutral low carbon development concept,therefore,it is urgent to explore a new process method to prepare high strength,high plasticity and excellent performance combination of lightweight austenitic stainless steel.The traditional austenitic stainless steel strengthening method adopts cold plastic deformation,which can obviously improve the strength of austenitic stainless steel,but also lead to a sharp decline in its plasticity.In this study,301 austenitic stainless steel was selected as the research material,and the grain refinement of 301 austenitic stainless steel was carried out by phase reversion process.The principle is to use the cold plastic deformation process and the phase reversion annealing process to coordinate the control of the two parts,refine the austenite stainless steel grains to the nanometer / submicron scale,and obtain the austenitic stainless steel strip with high strength and high plasticity.The evolution of the microstructure during cold deformation and phase reversion annealing was observed and analyzed.The effects of cold deformation process and reverse annealing process on the mechanical properties of 301 austenitic stainless steel strips were further studied,and the deformation strengthening mechanism was described.The experimental contents and results are as follows :(1)Different degrees of cold plastic deformation were carried out on 301 austenitic stainless steel with a thickness of 1.2 mm.The microstructure of cold deformation was observed and analyzed by OM,EBSD,TEM and SEM.The effects of different cold deformation on the mechanical properties of 301 austenitic stainless steel were studied.The results show that with the increase of cold deformation,the microstructure changes from equiaxed austenite to lath martensite and dislocation cell martensite,and the deformation mechanism changes from dislocation and shear band accumulation to twin-like deformation mechanism and TRIP mechanism.The tensile test shows that the twin-like crystal causes uneven plastic deformation.As a result,the tensile strength of the severely cold deformed sample decreases,while the elongation and hardness decrease with the increase of cold deformation.(2)The effect of annealing heating rate on cold deformation microstructure was studied.The samples with a certain cold deformation were subjected to reverse transformation annealing in the range of 650 °C-1120 °C.By changing the annealing heating rate,the evolution of grain size and microstructure was observed.The results show that the faster the annealing heating rate is,the more uniform the microstructure is and the smaller the size is.Under the slow annealing heating rate,the microstructure is more inclined to form a bimodal microstructure with double grain size.(3)The effect of cold deformation on the microstructure and properties of reverse transformation annealing was studied.The samples with cold deformation of 35 %,45 %,65 % and 70 % were annealed at a certain temperature.The effects of different cold deformation on the microstructure and mechanical properties after annealing were observed and analyzed.The results show that the larger the cold deformation,the smaller the grain size of the reverse transformation annealing,and the deformation texture formed in the cold deformation stage will remain in the reverse transformation annealing structure.The analysis of mechanical properties shows that the larger the cold deformation,the higher the elongation after annealing,while the tensile strength decreases slightly,and the hardness value decreases first and then increases with the increase of cold deformation.(4)The effect of annealing temperature on the microstructure of reverse transformation annealing was studied.Reverse transformation annealing was carried out on 35 % and 70 %cold deformed samples within a certain temperature range.The changes of microstructure of samples at different annealing temperatures were observed and analyzed,and the influence of annealing temperature on mechanical properties was analyzed.The results show that the higher the annealing temperature,the faster the reverse transformation rate and the more obvious the grain growth.With the increase of annealing temperature,the tensile strength and hardness decrease,while the elongation increases.The mechanical properties analysis shows that the 301 austenitic stainless steel ribbon with excellent performance combination of tensile strength of 1174 MPa,hardness of 315 Hv and elongation of 11 % can be obtained when the cold deformed sample is annealed at 750 °C for 10 min.