Case hardening... make your own home brew compound?

[yota]

Nitriding and carburizing surfaces is easy. What is difficult is to get the stuff to penetrate deeply. That's why they used to pour charcoal on top of forgings and just hammer it in.

I don't really understand the process myself (or many other parts of metallurgy) but I suspect it may use heat as a relay system for carbon atoms to get in. In other words, to get the inner iron layers to "steal" carbon atoms from the surface, and repeat the process, until it gets to the core. Therefore, the central consideration in such process is not the chemical composition of the hardening compound, but the carefully controlled environment the work piece is kept in.

This has to be the closest call ever!!!!

I think the point of case hardening, at least in the case of shotguns is to create a hardened outer shell to prevent wear, but to keep the inner layers unhardened to keep the forgings from cracking from repeated recoil. they were using steel forging processes to shape the parts.

the process is definitely a transfer of carbon, plus the quenching. I know that any engraving had to be done before case hardening.

 

[homebrewed]

The movement of a foreign atom into bulk material is called diffusion, and it occurs via one of two ways -- substitutional, where the foreign atom is about the same size as the bulk material's atoms; or interstitial, where the foreign atom is smaller so it can move in-between the bulk atoms.

Substitutional diffusion is much slower than interstitial. But given the large difference in atomic weights of carbon and iron, for case hardening it just about has to be interstitial. The diffusion rate also depends on the temperature -- higher = faster. The concentration of carbon on the exterior is important, too -- the higher, the better. You want a high concentration gradient to drive the diffusion.

The "best" approach might be to borrow a technology used for making semiconductors, called Ion Implanting. It can work much faster than diffusion, but the tool to do it is extremely expensive. It might be useful for niche applications but certainly not for general-purpose things where the selling price is king.