Abstract
Additions of Cr and Mn to steel are intended to increase hardenability (the ability to form martensite on cooling from austenite) and thereby improve the mechanical properties. However, conventional gas carburization of alloy steels containing Cr and Mn as well as Si will produce oxides of these elements (internal oxidation) near the surface (due to the oxygen potential of the carburizing atmosphere). Additionally, the oxidation of these elements locally reduces the hardenability of the alloy, creating the potential to produce non-martensitic transformation products (NMTP) near the surface. These oxides and the associated NMTP have been shown to decrease the fatigue resistance of carburized steels if they are not removed by subsequent machining operations. The objective of this study is to characterize the oxides, identify the NMTP and assess the degree of local alloy depletion in a carburized 8620 steel (0.21 C, 0.93 Mn, 0.023 S, 0.12 Si, 0.49 Cr, 0.38 Ni and 0.17 Mo).
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