Preoxidation prior to gas carburizing: Theory and its effect on pyrowear ® 53 alloy
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The absorption of carbon during gas carburizing of steel components is reviewed based on thermodynamic and kinetic considerations. The effects of chromium and silicon on carbon absorption are reviewed based on the thermodynamics of passive film formation in the presence of a carburizing gas. Finally, the merits associated with the use of preoxidation treatments prior to gas carburizing are discussed and the results of an in-depth analysis performed on carbon absorption in Pyrowear®1 53 alloy are presented based on preoxidation temperature.
Maximum carbon absorption was observed when using a preoxidation temperature of approximately 700/927° C (1292/1700° F) prior to carburizing Pyrowear 53 alloy at 927° C (1700° F) for 7.5 hr at a carbon potential of 1.16-1.19 using a 40% N2, 40% H2, and 20% CO endothermic carrier gas and vaporized methanol. This effect is believed to be related to the thickness of the oxide layer and to the roughness of the oxide/metal interface.
KeywordsAustenite Carbon Absorption Carbon Potential Surface Oxide Layer Furnace Atmosphere
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