Activation Energy of Nitriding Medium Carbon Ferromanganese Alloy

Investigation of some kinetics aspects of the reaction between nitrogen and medium carbon ferromanganese (MC-FeMn) was made. Nitriding process of fine medium carbon ferromanganese was carried out at temperature ranging from 973 to 1 223 K and time up to 480 min. Nitriding was carried out under nitrogen and hydrogen gas pressures. At temperature of 573 K, hydrogen gas was injected with pressure of about 0.2 MPa followed by injection of nitrogen gas up to 1.2 MPa. Sample mass was 35 g, nitrided in cylindrical chamber with 34 mm in inner diameter and 1 200 mm in length. The change in nitrogen pressure was taken as an indication for nitrogen pickup. The mass gain i.e. nitrogen pickup in kilograms per surface area (m2) was determined by time at different temperatures. Nitriding rate constants were calculated and the activation energy of nitriding process was derived from Arrhenius equation. The nitriding rate constant was found to be increased by increasing temperature of the reaction. The activation energy of nitriding process of fine medium carbon ferromanganese at time ranging up to 28 800 s is around 140 kJ/mol. It was found that the rate controlling step of the nitriding process of MC-FeMn is diffusion mechanism.