Effect of the Temperature and the Holding Time on Carburizing Treatment of 18CN4 and 22MC4 Steels

The surface of mechanical parts subjected to sever loads influence to a great extent the resistance to wear and fatigue. In majority of cases, producing of a hard superficial layer on a less tough substrate is conducive to an increased resistance to mechanical wear and fatigue. Hard layer of steel obtained by carburizing which bonded progressively to martensitic area of high hardness and to a core steel of lower hardness and greater toughness is an example of a good solution of the exposed problem. The high hardness of the carburizing layer is due to the increased concentration of carbon atoms located the interstitial sites of austenite before quenching. The lower hardness of the core after quenching is due to the presence of ferrite and pearlite components which appear if the cooling rate after austenitization becomes lower than the critical one. The objective of the present study was to obtain a cemented surface layer on low alloy steel by means of pack carburizing treatment. Different steel grades, austenitization temperatures as well as different soaking times were used as parameters of the solid carburizing treatment. During this treatment, carbon atoms from the cement powder diffuse toward the steels surface and form compounds of iron carbides. The effect of carburizing parameters on the rate transformation, on the thickness and morphology of carburizing layers, on structure and hardness of surface of steels produced by carburizing treatment was investigated by various characterization technic.