View Single Post
Old 09-10-2017, 10:39 AM
Registered User

rally is offline
Join Date: Sep 2007
Location: Australia
Posts: 896

There are many different hardening processes, the process depends entirely on the type of hardening you need and the type of material that you are hardening.

Are you needing to through harden or case harden ?

If you have a high carbon steel or a tool steel or silver steel then heating it to even dull red and quenching it vertically may work and that will give you a through hardening
Most Tool steels are typically vaccum hardened and gas quenched.

If you have a low carbon steel then you need to get carbon into the steel and that takes some sort of active process. Or maybe you need to get Nitrogen into it eg Nitriding
These processes work with very low carbon steels and will case harden.

. . . This all depends entirely on the steel alloy you are trying to harden

If the shaft is 4140 then you can Nitride (specialist process - cant do it at home) and that will give you a thin hard outer case.
The same material will through harden if just heated and quenched

If its some of the carbon mild free machining steels such as 1020, 1025, 1045 then that process may through harden (if quenched properly)

If its an old axle shaft or similar - EN25, EN39, EN36, 8620 etc then you would need to carburise and case harden.

Carburising can be done in a carbon rich gas environment, or done in a salt pot using molten cyanide salts - the two most popular commercial processes.
But there are others.
Sealed quench carburising or the old fashioned way to seal the part in a small container wrapped in carbon/charcoal - both processes but can take many hours - 10 to 13 hours is typical as the carbon literally has to permeate into the steel down to a mm or two. (Big gears are even longer)

The common thing with almost all hardening is there is a quenching process.
But again there are many different methods - usually depending on the material and the process.
The rapid cooling literally locks the crystalline structure of the material as it was at high temperature, do it too slowly and you might just temper the material back to normal !
Do it wrong and you will distort your shaft.

Quench from too high a temperature or with Oil/Water too low in temperature and you can distort or crack the steel.

Some processes and materials should be tempered after hardening (too brittle, or core refining), others not.

Without knowing the type of steel alloy you have - its either a case of lucky dip or potentially damaging the steel you have by trial and error.
Although most will temper back to normal.

A heat treater will probably be able to identify the steel and use a process to give you a good result and that is my recommendation.
Reply With Quote