| 200-series stainless steel uses Mn and N instead of expensive Ni,it has better corrosion resistance and mechanical properties,and the price is relatively low,it is widely used.200A austenitic stainless steel is a new type of low price stainless steel designed on the basis of 201 austenitic stainless steel,its Cr content is 17.217.6%,Mn content is8.959.56%,and N content is 0.140.19%.In order to understand whether the newly designed 200A austenitic stainless steel has commercial value,the dissertation systematically tests and researches the microstructure and corrosion resistance of 200A austenitic stainless steel,the focus was on the effects of solid solution aging and nitrogen content on the microstructure and properties of steel.The results of the study are as follows:200A austenitic stainless steel air-cooled microstructure after forging:the matrix is austenite,there is also a small amount of strip?-Fe phase;the organization is dense,the grain is small,the grain diameter is between 0.035-0.05 mm,and the grain grade is 5th between the 7th grade,there were no macrocracks and large inclusions,but there were a few microscopic pits.The energy spectrum analysis showed that the microscopic pits were chromium oxidition.After solution treatment at 1150?,the matrix of the steel is mainly austenite,and the microstructure is dense without macro-cracks.Compared with the air-cooled state after forging,the grain size of the steel increases significantly.After aging treatment at 700?,the stripe structure of?-Fe phase appears at the grain boundary.Compared with the solid solution state at 1150?,the grain size increases.After aging treatment at 800?,the compound phase precipitates at grain boundaries.Compared with 700? aging,the grain size increases.After aging at900?,there are more precipitation phases at the grain boundaries,which are full of grain boundaries.There are also a small amount of precipitated phases in the grain,and the precipitation phase develops into the grain and compared with the aging state at800?,the grain size increases.The hardness test results show that the microhardness of the three 200A austenitic stainless steels 1#?0.14%N?,2#?0.16%N?,and 3#?0.19%N?after forging in air-cooled condition is:255.2 HV0.5,292.88 HV0.5,268.06 HV0.5;After 1150? solution treatment:227.18 HV0.5,231.84 HV0.5,209.38 HV0.5;After 700? aging treatment:227.52 HV0.5,235.26 HV0.5,217 HV0.5;After 800? aging treatment:220.44 HV0.5,215.28 HV0.5,210.2HV0.5;900? after aging:230.72 HV0.5,234.52HV0.5,222.4 HV0.5.The polarization curve test results show that in the 3.5%NaCl solution,the corrosion potentials of three 200A austenitic stainless steels,1#?0.14%N?,2#?0.16%N?,and 3#?0.19%N?,are:-0.44997 V,-0.43542 V,-0.48282 V;Corrosion current densities were 3.59×10-5 A/cm2?1.72×10-5 A/cm2?1.61×10-5 A/cm2,compared.with3Cr13 stainless steel,the corrosion potential of 200A austenitic stainless steel is not much different from 3Cr13,but the corrosion current density of 200A austenitic stainless steel is less than half of 3Cr13.Compared with 304 stainless steel,the 200A austenite corrosion rate is higher than 304 stainless steel,and the corrosion resistance is worse than that of 304 stainless steel.Electrochemical reactive potential reactivation test?EPR?results showed that after aging treatment,the reactivation rate of three 200A austenitic stainless steels was between 1.75%and 34%.After aging treatment at 700?,when the N content was0.14%,the reactivation rate was the lowest,and the reactivation rate was 1.75%.Compared with the 300 series stainless steel,the intergranular corrosion resistance is better.In concentrated nitric acid immersion experiments,the corrosion rates of the three200A austenitic stainless steels 1#?0.14%N?,2#?0.16%N?,and 3#?0.19%N?were0.037 g/?h·m2?,0.100 g/?h·m2?,0.036 g/?h·m2?,there are many corrosion pits on the surface of the sample,and 3Cr13 stainless steel will rapidly generate a passive film after soaking to reduce corrosion.The corrosion resistance of 200A austenitic stainless steel is poorer than that of 3Cr13 stainless steel;the immersion test in 6%FeCl3 solution shows that:1#?0.14%N?,2#?0.16%N?,3#?0.19%N?corrosion rates of 18.4 g/?h·m2?,5.724 g/?h·m2?,and 15.717 g/?h·m2?.The pitting corrosion rate of 304 stainless steel is28.86 g/?h·m2?.The corrosion resistance of 200A austenitic stainless steel is better than that of 304 stainless steel.The immersion test in 1%NaCl solution shows that 1#?0.14%N?,2#?0.16 N?,3#?0.19%N?,were 0.297 g/?h·m2?,0.464 g/?h·m2?,and 0.169 g/?h·m2?,respectively;the immersion experiments in 5%Na2CO3 solution showed that:The corrosion rates of#?0.14%N?,2#?0.16%N?,and 3#?0.19%N?were 0.071 g/?h·m2?,0.152 g/?h·m2?,and 0.119 g/?h·m2?.The immersion test in 2%vinegar solution showed that the corrosion rates of 1#?0.14%N?,2#?0.16%N?and 3#?0.19%N?were:0.564g/?h·m2?,0.150 g/?h·m2?,0.211 g/?h·m2?.The uniform corrosion 200A austenite is better than 3Cr13 stainless steel,worse than 304 stainless steel;Intergranular corrosion cesistance is compared with 300 series stainless Steel;Acid corrosion cesistance tolerated is worse than 3Cr13 stainless Steel;Pitting corrosion resistance is better than 304 stainless steel;Acid and base resistance corrosion of salt meets the non-stick surface and testing specifications of domestic food metal cooking utensils in the national standard.The oxidation experiments at 800? showed that the oxidation rates of 1#?0.14%N?,2#?0.16%N?and 3#?0.19%N?were 0.02042 g/?h·m2?,0.03348 g/?h·m2?,0.02706g/?h·m2?.Refer to GB/T13303-199l standard,200A austenitic stainless steel has reached the level of complete oxidation resistance. |
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