Case Depth is the depth of the hardened case from the outer surface. Materials are case hardened to obtain Surface Wear Resistance, at the same time retaining the ductility of the core. Case depth may be microscopically measured a or determined as an Effective Case Depth at a specified hardness, which is determined by a Microindentation Hardness Traverse.
Decarburization depth is the depth from the surface, where carbon level is lower than the base metal, usually an undesirable side effect of heat treating processes in ferrous materials. This may be measured by metallographic examination of the microstructure of an etched specimen. Complete decarburization is caused by the total loss of carbon on the surfae, resulting in a light ferritic microstructure and can be microscopically measured. Partial Decarburization is indicated by a mixture of pearlitic and martensitic microstructure. The best way of measuring partial decarburization is from a microindentation hardness traverse.