Residual Carbon Inhomogeneity

Residual carbon inhomogeneity simply means that the carbon in the workpiece is not evenly distributed. This comes from incomplete austenitization, i.e., not the entire structure was properly transformed. When welding, you notice this as different hardness zones and higher crack susceptibility in the transition area. You can only counteract this with a proper homogenization annealing. The part must be fully brought to the correct austenitization temperature and held there long enough for the carbon to diffuse. Then let it cool slowly, otherwise you'll have the same problem again.