Measurement of Decarburization of Heat Treated Steel Surfaces

Decarburization is a significant problem in the heat treatment of steels as decarburization is detrimental to wear life and fatigue life of components. This presentation concentrates on its measurement by four procedures. Test results from an interlaboratory test of steels with spheroidize annealed, lamellar pearlite (normalized) and quenched and tempered martensitic microstructures were evaluated in an interlaboratory program. Opposite end portions of each specimen were turned incrementally and the turnings were analyzed for percent carbon. Then, the central part was sectioned, mounted and polished producing six mounts of each type. These specimens were rated by about a dozen different people in two ways. First, a “qualitative” evaluation was made where the metallographer, using a light optical microscope (LOM), scanned around the bar periphery looking for the greatest maximum affected depth (MAD), a qualitative assessment. Then, each operator made 25 randomly selected measurements of the MAD going around the bar periphery, a quantitative assessment. Microindentation hardness traverses were also made on each specimen to define the maximum affected hardness depth. The talk will compare the LOM qualitative with the LOM quantitative assessment of the MAD and also compare these results to the MAD determined by chemical analysis of the incremental turnings and the MAD determined by microindentation hardness testing as a function of matrix microstructure and alloy carbon content.