A THERMODYNAMIC STUDY ON CARBURIZING OF PLAIN CARBON AND ALLOY STEELS (OXYGEN PROBE)
Most of the published experimental data on the activity of carbon in austenite are for binary Fe-C and ternary Fe-X-C austenites, where X is an alloying element such as Mn, Si, Ni, Cr, Mo, and V. This prior data was obtained by equilibrating foil specimens with CO - CO(,2) or H(,2) - CH(,4) gas mixtures of a fixed composition. Commercial carburizing steels generally contain several alloying elements and the activity of carbon in these steels has been predicted from the numerical sum of the effects of each alloying element on the activity of carbon in ternary Fe-X-C austenite. Its validity has not been reported. The activity of carbon in commercial plain carbon and alloy steels was investigated in this study. Steel foils were equilibrated with an endothermic generator gas, the most common carburizing atmosphere presently used in heat treating industries. The activity of carbon was obtained from the measured partial pressures of CO, CO(,2), H(,2)O, CH(,4), and O(,2) of the furnace atmosphere. The carbon content of specimens was chemically analyzed. The activity of carbon in plain carbon steel, AISI type 1010, was found to be generally in agreement with previously reported data on pure iron at high carbon concentrations, but a noticeable difference was found at low carbon concentrations, especially at high temperature. The activity of carbon in alloy steels, AISI type 4820, 8620, and 9310, was found to be much higher than that calculated from the numerical sum of the effects of each alloying element on the carbon activity in ternary Fe-X-C austenite. The effect of alloying elements Si, Mn, and Cr, on the oxidation of these commercial steels during carburizing, was found to be about the same for a given temperature and oxygen partial pressure, regardless of differences in chemical composition.
"A THERMODYNAMIC STUDY ON CARBURIZING OF PLAIN CARBON AND ALLOY STEELS (OXYGEN PROBE)"
(January 1, 1986).
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