Analysis of decarburization of hypereutectoid FeC alloys and its application in evaluating the processing steps used to make Damascus steel swords

The decarburization of a hyperecutectoid FeC alloy at temperatures below the solubility limit of cementite (the A cm composition of the alloy) and above the pearlite temperature will produce two distinct diffusion layers at the decarburized surface. The first layer will be pure ferrite and the second layer will be austenite which will have transformed into pearlite on cooling (or martensite in quenched samples). A mathematical solution is presented here for the diffusion control of this decarburization process and it is shown that the relative thicknesses of the two layers is a fairly strong function of the temperature at which the decarburization is carried out. Damascus swords have a decarburized fold down their back side and this analysis is applied to one Damascus blade. It is demonstrated that metallographic analysis of the fold region allows an estimation of the forging temperature and the forging time for this blade.