Stress Corrosion Cracking Susceptibility of TP439 Stainless Steel in High Temperature Water Vapor
The stress corrosion cracking behavior of TP439 ferritic stainless steel in high temperature water vapor environment was studied,and the influence of water vapor and temperature on its stress corrosion cracking susceptibility was discussed.The stress corrosion cracking susceptibility of TP439 stainless steel in the water vapor environment at 400-600℃was investigated by a slow strain rate tensile test.The material used in the test was TP439 ferritic stainless steel,the main components were as follows:17.95wt.%Cr,0.47wt.%Ti,0.41wt.%Mn,0.22wt.%Ni,0.061wt.%Cu,0.026wt.%Mo,0.007wt.%Al,0.44wt.%Si,0.029wt.%P,0.017wt.%C,0.01wt.%N,0.005wt.%S,and the balance was Fe.The test strain rate was 2×10‒5 s‒1,the test environment was high-temperature air and high-temperature water vapor(10%Ar+90%H2O),and the oxidation temperatures were 400℃,500℃,and 600℃,respectively.A scanning electron microscope(SEM,Quanta 2000)was used to observe the fracture morphology of the sample,and an energy dispersive spectrometer(EDS,INCA)was used to analyze the oxidation product composition near the fracture.Under the same strain rate(2×10‒5 s‒1),with the rises of temperature in the range of 400-600℃,the yield strength,tensile strength and fracture energy of TP439 stainless steel in air and water vapor environment gradually decreased,the elongation increased gradually.At 400℃and 500℃,the tensile strength of the samples in the water vapor environment were lower than those in the air environment,the elongation was increased compared with those in the air environment.At 600℃,the mechanical properties of the samples in the water vapor environment were not significantly different from those in the air environment.The stress corrosion cracking susceptibility of the samples in 400℃,500℃,and 600℃water vapor environments were 0.7%,1.2%and ‒2.8%,respectively,and the stress corrosion cracking susceptibility was low.The samples exhibited ductile fracture in the water vapor environment at 400-600℃.The fracture morphology was composed of dimples and micropores,and the necking phenomenon was significant.No secondary cracks were found near the fracture.The stress corrosion cracking susceptibility of the sample was low.When the temperature was increased in the range of 400-600℃,the dimple features of the fracture were more obvious,the fracture area gradually narrowed,and the degree of necking gradually increased.In the water vapor environment at 400-600℃,the main elements of the oxide film near the fracture of the sample were Fe,Cr,O.At 400℃and 500℃,the oxide film on the surface of the sample was smooth and level,and the atomic percentages of Cr were 17.21%and 11.20%,respectively.When the temperature rose to 600℃,many fine whisker-like oxides were observed on the surface of the oxide film near the fracture of the sample.The Cr content on the surface of the oxide film decreased to 1.36%,mainly composed of oxides containing Fe.Water vapor promotes the stress corrosion behavior of TP439 stainless steel.Based on the analysis of stress corrosion cracking susceptibility index and fracture morphology,the stress corrosion cracking susceptibility of TP439 stainless steel is low in water vapor environment at 400-600℃with strain rate of 2×10‒5 s‒1.
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万方数据
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