High Temperature Oxidation Behavior Of Fe-Cr-Si Steel

In this paper,the high temperature oxidation behavior of Fe-5Cr-0.2Si steel andFe-10Cr-0.2Si steel were studied by Thermo Gravimetric Analyzer?TGA?.The oxidation rate constants and activation energy of two steels were calculated to compare the antioxidant capacity.And the scale structures of two steels were analyzed.The oxidation behaviors of experimental steels in air at different time were studied by a tubular resistance furnace.The internal and external oxidation transformation mechanism of the steels was provided by analyzing the scale structure.The oxidation behaviors of experimental steels in the water vapor were investigated by TGA,and the effect of water vapor on the scale structure was observed.The oxidation kinetics of 5Cr steel and 10Cr steel oxidized in air for 60min follows the linear law.By establishing the oxidation kinetic model,the activation energy of 5Cr steel is 114.0099KJ/mol,and the activation energy of 10Cr steel is 235.3030KJ/mol.Thus,10Cr steel has stronger oxidation resistance.The oxide scale of the two steels is a two-layer structure:an outer layer composed of Fe oxides and an inner layer consisted of Cr-rich oxides.The Cr₂O₃ in the scale reacted with oxygen to form gaseous CrO₃,which volatilized the Cr-rich oxide.As the oxidation temperature increased,the volatilization became more serious,resulting in a large number of voids near the interface between the inner layer and the outer layer.It was found that the scale became thicker with time by isothermal oxidation in air at1000?.The oxidation kinetics of 5Cr steel follows a linear law with the oxidation time up to 180min,while that of 10Cr steel follows a near-parabolic law.As the Cr content increases,the resistance of the scale to the double diffusion of ions increases,which makes the scale more protective,and the diffusion rate of ions through the scale are reduced.The relatively small ion diffusion rate results in a flatter scale/substrate interface of the 10Cr steel than the 5Cr steel.The scale of multi-voids was observed in water vapor with voids extended into the interior of Fe₃O₄ layer,and provided a channel of the transportation of water vapor.As the Cr content increases,the transition temperature of steels from the linear law to the parabolic law increases.The 5Cr steel followed the linear law when oxidized at 800?and900?for 60min,and followed the parabolic law at 1000?,1100?and 1200?.However,the 10Cr steel still followed the linear law after oxidized at 1000?for 60min.At 1100?,the 10Cr steel obeyed the linear law when oxidized for 1100s,followed by a parabolic law,and the oxidation rate obeyed the parabolic law at 1200?.Under high temperature and high oxygen partial pressure,Cr-rich oxides reacted with water vapor to form a hydroxide compound,resulting in the failure of the oxidation resistant inner layer.