Preparation Of Micro/Nano Structure 316L Austenite Stainless Steel And Its Tissue And Property

316L austenitic stainless steel is the that steel that can survive to many different environment.Due to its excellent corrosion resistance,machinability and weldability,316 L stainless steel（316L SS）was used in many kinds of field,for instance: petrifaction,ocean and paper industry.However,it has a crystal pattern of face-centered cubic and a component of low carbon,which conduct its poor strength and hardness.This characteristic was limiting its wildly using in many vital field.In order to improve its comprehensive mechanical property,the method of thermit reaction was used to synthesis the 316 L stainless steel with micro/nano structure.By reason of the Al powder wasn’t react completely and rest of them was blended in the alloy,there are some of ferrite in the matrix of steel.So,the purpose of this study is to eliminating the ferrite by add different content of Fe₂O₃ powder,investigating the changing rule of microstructure,mechanical property and corrosion resistance through rolling and subsequent annealing,building the foundation of expanding to industrial manufacture.Finally,drawing the conclusions as follow:1.Adding superfluous Fe₂O₃ can really reduce the Al content in steel synthesised by thermit reaction.When the superfluous ratio of Fe₂O₃ was 2.5%,the Al content in prepared 316 L SS is 1.74% and the volume fraction of ferrite is 4.1%.When the superfluous ratio of Fe₂O₃ was 5%,the Al content in prepared 316 L SS is 1.3% and the ferrite was disappeared.When the superfluous ratio of Fe₂O₃ was 7.5%,the Al content in prepared 316 L SS is 0.99% and there still have no ferrite.In addition,there are some FeCrMo phase exist in the matrix.Hence,5% of superfluous ratio of Fe₂O₃ is the ideal parameter of synthesising 316 L SS by thermit reaction.Micro/nano structure was exist in those steels prepared with different superfluous ratio of Fe₂O₃ through TEM characterization.2.There has about 21.4% ferrite appeared in the 316 L SS,which was rolled with the parameter of 800℃-40%+600℃-80%.Moreover,the mean grain size of steel was grown up from 23 nm to 47 nm.And the proportion of micro-grain was also changed: the percentage of micro-grain was increased from 8.9% to 15.6%.Comparing to as cast steel,the yield strength of rolled specimen has a dramatic increase from 207 MPa to 1007 MPa,and the break strength was also increased from 376 MPa to 1030 MPa.Yet,the elongation of the steel was droped to 2.4%.In addition,the corrosion resistance of steel has been optimized in the environment of 0.5M H2SO4 solnsolution after rolled.3.In order to regulate and control the microstructure of 316 L SS further,the rolled specimens was suffered annealing at the temperature of 800 ℃ with the time of 20 min,40min,60 min,80min.After 20 min,the percent of ferrite was droped from 8.4% to 3.2%,and the mean grain size was increased from 47 nm to 57 nm.Moreover,the steel still have the micro/nano structure.As the time of annealing increasing,the percent of ferrite present a growing tendency.At last,it has arived at the value of 6.9%.However,the micro/nano structure was disappeared after 40 min.There has a small drop of steel’s strength.After 20 min,the yield strength and the break strength was 464 MPa and 770 MPa,respectively.Well,its elongation has a big increase to 21.5%.As the time of annealing increasing,the strength present a small drop and the elongation increased dramatically.To conclusion,the 316 L SS obtained the ideal balance of strength and plasticity.