Research On High Temperature Oxidation And Grain Growth Behaviors In Austenitic Stainless Steels

This article has studied the heat resistance and oxidation behavior and kinetics rules of the three commercial austenitic stainless steel—304, 316L, 904L from the perspective of high-temperature oxidation resistance. Meanwhile, analyzes from thermodynamics and kinetics of austenite grain growth phenomenon, for steel production and development stainless steel products in the future to provide some reference and austenitic stainless steel at high temperatures application production has certain directive significance.By means of isothermal testing, the high temperature oxidation behaviors of the 304, 316L, 904L austenitic stainless steel have been studied in the temperature 700℃, 800℃, 900℃and 1000℃. The profile morphologies and phase structure of oxidation 1ayers were observed and analyzed by SEM and XRD, and oxidation curves was fit by least-square method. The results show that 304 stainless steel in the 700⁸00℃oxidation has excellent antioxidant properties, belongs to the complete antioxidation level; at 900℃, 304 surface formation of oxidation film was flaking, belongs to the antioxidant level; at 1000℃304 belongs to the inferior oxidation resistance level. 316L austenitic stainless steel in 700⁹00℃belongs to complete antioxidant level, at 1000℃it has bad oxidation characteristics. 904L in 700¹000℃belongs to complete anti-oxidation level. The oxidation activation energy of 304, 316L, 904L are 222.57kJ/mol, 241.37kJ/mol and 253.78kJ/mol. The reaction are controled by Cr, O diffusion in the oxide.In the temperature range between 700℃and 800℃, the oxide layer are mainly composed of Cr₂O₃ and Fe₃O₄. Above 900℃, the oxide layer are mainly composed of Fe₃O₄, Fe₂O₃, FeCr₂O₄å’ŒNiCr₂O₄, and the Cr₂O₃ disappeares. Because W_Cr of 316L and 904L is higher, Cr₂O₃ exists in oxide layer. At 1000℃, the oxidation kinetics of 304 follow apara-linear rate law. The oxidation kinetics of 316L follow linear rate law, and catastrophc oxidation was happened. In contrast, the kinetic curves of 904L still follow the parabolic rate law even after 100h of exposure. Comparing with the high temperature oxidation susceptibility of the three mentioned austenitic stainless steel, we can found that 904L has the best oxidation resistance. 316L has the good oxidation resistance at temperature below 900℃, but it was severely affected by temperature, and catastrophic oxidation was happed at 1000℃. 304 has the good oxidation resistance. The growth law of austenite grain in 304, 316L and 904L austenitic stainless steel was investigated by metallographic technique and theoretic at 800¹000℃. The values of lime and activation energy for austenite grain growth in 304, 316L and 904L were worked out based on the experimental results, and the mechanism of the grain growth was discussed. The results show that when heating temperature is lower than 900℃, the experimental steel has a smaller grain dimension; when heating temperature is above 1000℃, the austenite grains grow rapidly. The variation of average austenite grain size with the isothermal time follows Beck's law:D=Ktⁿ, the relationship between the average austenite grain size and heating time is direct proportion. The isothermal growth equation of austenite grains obey the parabolic expression. The values of boundary migration activation energy for austenite grain growth is measured to be 164.8kJ/mol for 304, 178.6kJ/mol for 316L, and 192.7kJ/mol for 904L. The temperature dependengce of the average austenite grain size of the steel can be well describied by an Arrhenius-type equation:D=5.75×10⁴exp(-164.8×10³/RT) for 304; D=2.11×105exp(-178.6×10³/RT) for 316L; D=2.38×104exp(-192.7×10³/RT) for 904L.