Measurement of Decarburization

Decarburization is a significant problem in the heat treatment of steels as decarburization is detrimental to wear life and fatigue life of components. This paper discusses some of the factors that cause decarburization while concentrating upon its measurement. Results will be given showing a simple screening test that the writer used on bars for coil springs and how the test results correlated to actual microscopical measurements. Test results will be shown as to how a scaled versus a descaled surface affects decarburization as a function of the austenitizing temperature. Test results from an interlaboratory test of steels with spheroidize annealed, lamellar pearlite (normalized) and quenched and tempered martensitic microstructures were evaluated by about a dozen different people 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 scanned around the bar periphery looking for the greatest maximum affected depth (MAD). Then, each operator made 25 randomly selected measurements of the MAD going around the bar periphery. The talk will show the comparison of the qualitative versus the quantitative assessment of the MAD and compare these results to the MAD determined by chemical analysis of the incremental turnings and the MAD determined by microindentation hardness testing.