Study On Rolling Experiment And Microstructure And Properties Of 321 Stainless Steel Foil

With the wide application of microfabrication and micro-electro-mechanical system in aerospace,precision instrument,electronics and other fields,the demand for stainless steel ultra thin strip is increasing day by day,and higher requirements are put forward for its surface quality.The traditional method of preparing ultra thin strip is synchronous rolling.Due to the limitation of the minimum rolling thickness,the thinning capacity can only be enhanced by reducing the roll diameter,increasing the support roll,and by means of intermediate annealing.Due to the complicated structure,difficult maintenance and complicated process of rolling equipment,a lot of costs are added in the actual production.Based on the above background,this paper,supported by the national natural science foundation of China(NSFC)project "experiment and mechanism research on the phenomenon of overextension in ultra-thin strip forming",is devoted to exploring a low-cost asynchronous rolling process of ultra thin stainless steel strip without intermediate annealing.Mainly from the reduction of rolling force,reduction of rolling pass,reduction of intermediate annealing link to carry out the research;At the same time,the evolution law of microstructure during asynchronous rolling and annealing was studied to provide theoretical basis for subsequent industrial production.In this paper,the main research methods are as follows:through comparative experiments,the influence of rolling parameters such as different speed ratio and tensile stress on asynchronous rolling process is studied;the deformation mechanism and mechanical property change mechanism of stainless steel during cold rolling were analyzed.The effects of annealing temperature,annealing time and cooling mode on microstructure and properties of stainless steel ultra-thin strip were studied by different heat treatment processes.The main research work and achievements are as follows:(1)The influences of rolling process parameters such as the anisotropic ratio and the front and rear tensile stress on the rolling force and the thickness of the final rolling were studied by comparative experiments.Taking the single pass 40%reduction rate as an example,when the anisotropic ratio increased from 1.0 to 1.4,the rolling force decreased from 46.996t to 10.281t,reducing by 78.1%.Under the condition of constant rolling force and the same rolling pass,the final rolling thickness decreased by 39.5%when the different speed ratio increased from 1.05 to 1.40.When the post-tension stress increased from 75MPa to 150MPa,the rolling force decreased by 13.8%.It is found that the contribution of different speed ratio to the reduction of rolling force is much greater than that of tensile stress.Therefore,in the process of thinning,it is preferred to increase the anisotropy ratio.When the anisotropy ratio reaches the upper limit of equipment or working condition,the tensile stress will be increased.(2)0.02?0.1mm 321 stainless steel foil with good surface quality was successfully obtained through 9 passes without intermediate annealing by the selfdeveloped four-high reversing mill combined with asynchronous rolling technology was used to reasonably match the rolling process parameters.Through the pressure rate of 35%,60%,80%of samples for observation and performance detection.It is found that there exists deformation induced martensitic transformation in asynchronous rolling process,and martensitic content increases slowly with the increase of pressure rate and then increases rapidly.When the pressure rate increased to 50%,the volume fraction of martensite increased from 0%to 9.7%.When the pressure rate increased from 50%to 80%,the martensite volume fraction increased rapidly from 9.7%to 52.1%.The texture in the direction of martensite<110>increases with the increase of the compression rate.Compared with the raw materials,the tensile strength of the sample with 80%compression rate increased from 670MPa to 1527MPa,the elongation after fracture decreased from 43%to 0.4%,and the corrosion rate increased from 0.0022mm/a to 0.4986mm/a.(3)The influence of annealing temperature,annealing time and cooling mode on the mechanical properties of the ultra-thin stainless steel strip was studied by annealing the cold-rolled samples with a pressing rate of 35%,60%and 80%.The results show that the comprehensive mechanical properties improve with the increase of annealing temperature.With the increase of annealing time,the comprehensive mechanical properties decrease.With the increase of cooling rate,the comprehensive mechanical properties are improved.(4)By taking the sample with 35%reducation cooled in furnace after annealing at 1050? for 3min,obtaining gradient grain size organization.The surface deformation induced martensite by reverse change have been the austenitic grain size is 1 ?m,core by retained austenitic recrystallization of austenite grain size in 13?m,it has good mechanical properties,tensile strength can be up to 704MPa,elongation is 31.8%,PSE is 22.39GPa·%.