Hardening my piston

[MarcDV]

Hi Guys, Re: case-hardening - just adding my two penneth here. There is some confusion about the terms describing the process. To increase the carbon content of a mild steel (or low-carbon steel) coupon (test piece) by the heating of the coupon in a highly carbon enriched environment is correctly known as carburizing. Case hardening is a separate process involving heat treating on the coupon to change the molecular structure of the now carbon-rich skin of the carburized part and to quench it, thus ‘locking’ the grain structure of the carbon rich skin in a hardened (martensitic) structure. If the carburized layer is particularly thick, it can be hardened as stated and then tempered back to adjust the hardness similar to the tempering of “through hardened” steels.

The chemical Casenite used for producing a very thin carburized layer with an oxy-acetylene torch is still available online by mail order from Brownells. This process is not for the impatient because it does take a lot of time. The encasing of the coupon in a metallic box stuffed with carbon fragments still works, but again, it takes many hours to achieve a result.

The best and most accurate and elegant method of carburizing a low-carbon steel is by immersion in a cyanide bath (or a more exotic gaseous nitride rich muffle-furnace). Sadly, these processes are usually only used by professional heat treatment companies as, obviously there are many hazards and more regulations than you can shake a stick at. I have had high carbon case thicknesses of hardenable material of 0.03 inch (0.75mm) on air-gun parts before.

Good luck with this,

Marc DV.

[plumbgun]

Just to say I really appreciate the helpful comments that I have received. I have learnt quite a bit from what has been said, and if I do manage to get the item hardened to a degree that it will stand the wear and tear it has to, I will write and say exactly what I did.

thanks again,

Paul M.