Determination of decarburization in steel

A computer program has been written that optimizes the fit between the microhardness numbers determined in a cross section traverse and the diffusion equation corresponding to Fick’s second law of diffusion. Using an iterative procedure, the program minimizes the RMS error between the microhardness numbers and three constants corresponding to (1) the product of diffusivity and time, (2) surface hardness, and (3) core hardness. The type of decarburization, as described in SAE J419, “Methods of Measuring Decarburization,” may also be evaluated by determining the base carbon concentration and the near-surface carbon concentration from the same sample. Test samples of 5160H and 6150H steel were decarburized and evaluated using this procedure.