Pack Carburizing: Characteristics, Microstructure, and Modeling

Abstract

Pack carburizing or solid carburizing, which is one of the case-hardening processes, is the enrichment of the depth of low-carbon steels with carbon that has been produced from a solid compound. The diffusion of carbon atoms is enhanced by energizers or activators, such as barium carbonate, calcium carbonate, potassium carbonate, and sodium carbonate that may present in the carburizing compound. Study of case depth or hardenability is one of the important parameters in carburized steels. For determining case depth, microhardness testing is done on a cross section of carburized specimens. The alloys that are subjected to pack carburizing are usually low-carbon and low-alloy steels. This process leads to samples with a combination of high surface hardness and high core toughness and to an impact strength that is required for many engineering parts, such as gears and bearings, according to the formation of martensitic microstructure in the outer region of the steel and ferritic–pearlitic microstructure in the core region. In this entry, we discuss the effect of various energizer materials, carburizing time, and steel chemical composition on the case depth and mechanical properties of low-carbon steels. In order to compute the optimum value of the energizer material that will lead to the specified case depth, a numerical procedure was used. Also, the correlation between hardenability curves and the microstructure of carburized steels, as well as the boundary conditions of carburizing and decarburizing phenomena in the presence of some energizer materials, is studied. A comparison between pack carburizing and other carburization techniques, as well as the effect of the filling approach to pack carburizing on hardenability, is discussed. Also, the differences between the mathematical modeling of this process performed by Fick’s laws and the actual position of this process are highlighted.