Carburization Resistance of Fe-25Mass%Cr-38%Ni-1.8%Si-1.5%Mo Alloy in Laboratory CH₄-CO₂-H₂ Gas Environments at 1000~1150°C Available to Purchase

Thermodynamic equilibrium calculations were conducted to understand the carburizing environment of ethylene pyrolysis in the petrochemical industries. Calculated equilibrium, Po₂, was estimated to be in the range of 10^-21 to 10^-19 atm for the operating condition of actual ethylene pyrolysis plants. In this environment, chromium oxide was stable for up to 1030~1040°C. However, Сr₂О₃ converted to chromium carbides such as Сr₇С₃ and Сr₂С₃ above 1030~1040°C. Based on the calculations, laboratory carburization tests were carried out. Chromium was an effective alloying element, and more than 25mass%Cr was necessary for austenitic alloys to provide protection against carburization environments at 1000°C. Chromium as a Cr₂O₃ protective oxide scale on the metal surface prevented carbon ingress for alloys. At 1100 and 1150°C, however, Cr₂O₃ scale did not provide protection, and silicon oxide, which formed underneath the Сr₂O₃ scale, was effective in reducing the carbon ingress. This behavior agreed well with the thermodynamic stability of the oxide scales. Alloy of Fe-25%Cr-38%Ni-1.8%Si-1.5%Mo had excellent carburization resistance similar to Fe-32%Cr-43%Ni-1.7%Si cast alloy in the laboratory tests.