Effect Of Cold Rolling On Microstructure And Mechanical Properities Of 316LN Austenitic Stainless Steel

316LN austenitic stainless steel has excellent toughness and plasticity,high temperature oxidation-resisting and corrosion resistance,and is widely used in food and chemical engineering,however,the strength of the austenitic stainless steel under solid state is relatively low,so austenitic stainless steel is rarely used for structural materials,usually through the work hardening and other methods to improve its overall performance to meet its requirements.Cold rolling,as an effective method of work hardening,is often used as a means to improve the performance of stainless steel.In recent years,many scholars have carried out extensive research on microstructure and mechanical properties after cold-rolling at home and abroad,so far,the effect of cold-rolling and cryorolling on the microstructure and properties of 316 LN austenitic stainless steel has been seldomly systematically studied,and the research objects by cryorolling are limitation in non-ferrous metal at home and abroad.In view of the above,the effect of cold-rolling deformation on the microstructure and properties of316 LN austenitic stainless steel will be comprehensively studied in this paper,which will provide experimental basis and technical support for the development and application of 316 LN austenitic stainless steel..The paper took 316 LN stainless steel as the research object,then the samples were subjected to cold rolling and cryogenic rolling,changes of mechanical properties of 316 LN stainless steel were systematically analyzed,microstructure evolution of austenitic stainless steel after rolled were observed and analyzed by means of metallographic microscope(OM)?scanning electron microscope(SEM)?transmission electron microscope(TEM).The results show that the deformation-induced martensite transformation occured in the process of cold rolling and cryorolling,and the greater deformation,the greater volume fraction of the deformation-induced martensite transformation.The volume fraction of deformation-induced martensite transformation was from 11.1%(30%)to 72.3%(90%)after cold rolling,and the volume fraction was from 58.7%(30%)to 78.7%(50%)under cryorolling.With the increasing of deformation to 70%,the austenite under solid solution had completely transformed into the martensite.By comprehensive comparison,the rate of the deformationinduced martensite transformation under cryorolling is much higher than that under cold-rolling,and the microstructure of austenite can be totally transformed intomartensite.In the case of cold rolling,the main component of deformed microstructure are dislocation multiplication and tangles after small deformation,meanwhile,a small amount of deformation twins and martensite are observed.With the increasing of deformation,the deformation structure is dominated by deformation twins,accompanied by a small number of high-density dislocation walls and dislocation cells,while deformation induced martensite appears in large numbers.In the process of cryorolling,a large number of martensite have been formed when the deformation is small.When the deformation is further increased to 70%,the martensite transformation has occurred completely.The hardness and strength of austenitic stainless steel were both increased with the increasing of deformation,they increased rapidly in prophase and slowly in late stage,but the elongation was the opposite.The hardness and strength after cryorolling were much higher than that after cold rolling at the same deformation.After 90%deformation,the hardness of austenitic stainless steel after cryorolled was about three times the hardness of original sample,the yield strength and tensile strength were respective about 7 times and 3 times as much as the original sample.The hardness after cold rolling was 2.6 times as much as the original sample,the yield strength and tensile strength were 4.9 and 2.2 times as much as the original sample.The tensile fracture changed from typical ductile fracture to quasi-cleavage fracture and ductile fracture.The elongation decreases rapidly with the increase of rolling deformation,contrary to the trend of mechanical properties: the elongation of the specimen decreased from 3.5%(30%)to 2.5%(90%)under cold rolling,and was 2.3%(30%)to1.5%(90%)under cryorolling.