Microsturcture And Properties Of Circulating Recrystallization Of 0Cr21Mn17MoNbN0.85 Steel

Austenitic stainless steel is a common metal material.Compared with traditional austenitic stainless steel,high nitrogen austenitic stainless steel has many advantages,such as good yield strength,tensile strength and ductility,high strength and fracture toughness,high strain strengthening potential,and good corrosion resistance.High nitrogen austenitic stainless steel of the excellent propertie is an important material in the production and life,the research on the properties of high nitrogen austenitic stainlesssteel has become the focus at home and abroad.Metals can be refined by cold plastic deformation,mechanical properties of metals can be improved by this way,and grain can be refined by annealing at appropriate temperature.Whether this method can be used to make high nitrogen austenitic stainless steel to refine grain by cyclic rolling and recrystallization is the research content of this experiment.In this paper,0Cr21Mn17MoNbN0.85 high nitrogen austenitic stainless steel is prepared by smelted at atmospheric pressure,then solution treatment(holding at 1140 ~oC for 8 h)and cold rolling mill was used to roll it four times.The total amount of down rolling was 20%each time.Annealing and recrystallization treatment at 1000~oC(holding for1 h)was carried out between the two rolling cold deformation treatments.In order to eliminate the work hardening and internal stress of cold deformed metal,the third rolling sample was recrystallized at 900,950,1000 and 1050~oC for 1 h.The microstructure and mechanical properties of the material were analyzed under different processing conditions.The results show that the grain is refined obviously after three times rolling,and the plastic deformation is mainly plane slip,forming deformation texture composed of slip band.After recrystallization,the grain distribution is uniform,the hardness shows a downward trend,and then tends to be stable.The microstructure of sintered samples was observed by SEM.Electronic universal testing machine(WDW-200)was used to conduct tensile test.The microstructure of stretched samples was analyzed by SEM.The effects of recrystallization temperature and cold deformation on the properties of high nitrogen nickel-free austenitic stainless steel were studied.The results showed that:(1)In the as-cast structure of high nitrogen nickel-free austenitic stainless steel,there are a large number of dendrites and nitrogen holes,and there are unsolved flake nitrides between dendrites.Nitrogen holes can be welded during rolling.High nitrogen and nickel-free austenitic stainless steel was treated by solution at 1140 C for8 hours and then quenched by water.The obtained high nitrogen and nickel-free austenitic stainless steel has a single phase austenite microstructure with a large number of annealing twins and finer grains.(2)The microstructure of nickel-free austenitic stainless steel of high nitrogen steel has changed after cold plastic deformation(rolling).The grain size decreases and annealing twins appear.The existence of twins hinders the movement of dislocations,which makes high nitrogen steel with high strength,hardness,good plasticity and toughness.(3)The strength of high nitrogen nickel-free austenitic stainless steel can be improved by cold plastic deformation.With the increase of deformation,the yield strength and tensile strength increase,but the plasticity decreases.The comprehensive mechanical properties of 50%deformation state are the best.By annealing and recrystallization treatment,the work hardening phenomenon can be eliminated and the plasticity can be improved.(4)In the process of cyclic recrystallization,the properties of high nitrogen and nickel-free austenitic stainless steel after cold-plastic deformation reach a certain extent.The comprehensive property of 60%total deformation in the fourth rolling is lower than that of 50%total deformation in the third rolling.(5)It can be seen from the observation of the tension port that the plasticity of nitrogen-nickel-free austenitic stainless steel can be improved with the increase of recrystallization temperature.The higher the recrystallization temperature,the larger the dimples,the larger the size and the stronger the plasticity.The recrystallization temperature should be higher than 900℃,and the comprehensive properties of recrystallization treatment below this temperature are poor.