Influence of Time and Temperature on Decarburization Rates for AISI 52100 and 1095 High Carbon Steel

Decarburization of high carbon steels during annealing results in lower surface hardness after heat treatment. Typically, such chemical alteration at the surface is undesirable, and measures are taken during processing to prevent or restore lost carbon to ensure uniform mechanical properties of finished products. Significant efforts have been made towards preventing decarburization, as well as understanding the relationship between annealing time, temperature, and decarburization rate. However, much of the research has placed emphasis on steels with lower carbon content, ranging from 0.3 wt%C up to the eutectoid point. The current project focuses on decarburization of steels with carbon concentrations above the eutectoid concentration. Two high carbon steels (AISI 52100 and AISI 1095) were held at three temperatures (below Ac₁, above Ac_cm, and between Ac₁ and Ac_cm) for extended periods (12, 24, and 36 hours). The steel samples were subsequently quenched in oil or cooled in air. The decarburization depths were determined using microstructural analysis and micro-indentation hardness testing. The information was then used to determine the decarburization rates and compared to decarburization predictions based on diffusivity of carbon in austenite, ferrite pearlite, and austenite cementite microstructures.