Carbothermic reduction of oxides during nitrogen sintering of manganese and chromium steels.

Abstract

To interpret nitrogen sintering of chromium and manganese steels without the formation of deleterious oxides, but with manganese and carbon the formation of deleterious oxides, but with manganese and carbon modifying the local microclimate, the role of the volatile Mn and modifying the local microclimate, the role of the volatile and Mn carbothermic reactions were considered. carbothermic reactions were considered. Reduction of Cr Reduction of Cr 2 2 O About 3 3 by Mn vapour by Mn vapor is always favourable. is always favorable. CO is an effective reducing agent, however, whereas CO is an effective reducing agent, however, whereas at atmospheric pressure it will reduce FeO at730°C, temperatures some at atmospheric pressure it will reduce FeO at730 ° C, temperatures some 500 and 700°C higher, ie above those for conventional sintering, are 500 and 700 ° C higher, ie above those for conventional sintering, are necessary for reducing Cr necessary for reducing Cr 2 2 O About 3 3 and MnO, respectively. and MNO, respectively. Accordingly partial Accordingly partial pressures must be considered and the sintering process is modelled at a pressures must be considered and the sintering process is modeled at a conglomerate of several surface oxidised alloy particles surrounding a pore conglomerate of several surface oxidised alloy particles surrounding a pore with graphite present and a tortuous access to the nitrogen-rich atmosphere with graphite and present a tortuous access to the nitrogen-rich atmosphere containing some water vapour and oxygen. containing some water vapor and oxygen. The relevant partial pressures The relevant partial pressures were calculated and reduction reactions become thermodynamically were calculated and reduction reactions become thermodynamically favourable from 200°C. favorable from 200 ° C. Kinetics, however, dictates availability of CO and Kinetics, however, dictates availability of CO and the relevant reactions are the water-gas, C + H the relevant reactions are the water-gas, C + H 2 2 O = CO + H O = CO + H 2 2 from 500°C from 500 ° C and the Boudouard, C + CO and the Boudouard C + CO 2 2 = 2CO, from 700°C. = 2CO, from 700 ° C. Discussion of sintering Discussion of sintering mechanisms is extended to processing in semi-closed containers, also mechanisms is extended to processing in a semi-closed containers, also possessing specific microclimates.