I asked him what he was planning on case hardening and he replied.
As for the use I was thinking about the slide of a 1911 style pistol. It sounds like it might not be as feasible as I had thought it would be.
Damascus steel was created in India and was used in sword making from 300 BC to 1700 AD. It is produced my layering and folding alloys of steel and forging them together. At this point in time it was the impurities in the steel that gave it its strength, the long work hammering layers together in a wood burning furnace imparted carbon to the steel between every layer.
Case hardening is from that era and it was originally used as a way of turning soft low carbon steel into a more durable soft steel encased in high carbon steel because they lacked modern metalworking processes that we have today to produce strong homogenous high carbon and steel in efficient process. Before case hardening I think they made gun barrels out of brass.
What he is working with is a piece of metal made of hundred of layers of high carbon stainless steel forged together. Case hardening would color it, but it probably wouldn't do anything to strengthen it, I think it would probably make it brittle. An acid bath would make it darker and have more contrast. Hot bluing it would basically do the came thing with ferric oxide.