HI Wolfie,
Hardening and tempering of steels is a vital part of engineering and you really need to master the process as much as any other, here are a few tips I hope may help. Only medium and (preferably) high carbon content steels will harden, most stainless steels will not harden. You can ‘case harden’ mild (low carbon) steels but that is another kettle of fish entirely.
Hardening and tempering is a two stage process. First you harden (Durr!) by heating to cherry red and holding there for a few minutes (soaking) to allow the changes in the steel to take place. It is then quenched in oil or water depending on the steel type to ‘freeze’ the new properties in the steel. However it is then too hard and brittle for most purposes.
It must be ‘tempered’ to draw out some of the hardness and impart a toughness depending on the purpose. If a tool is to be hit ( cold chisel, punch etc) it needs more toughness (higher quenching temp) if it is to cut it needs more hardness (e.g. scriber, file). These temperatures are quite critical but easy to spot on a hardened steel which is polished before heating for tempering, They range from pale yellow (coolest – less temper) e.g. turning tools, and pale blue (hottest – more temper) e.g. springs.
There is plenty on the web about this but here is a
page, and a
video to get you started. There is also a good book in the Workshop range available
here.
Best regards
Terry
Edited By Terryd on 20/10/2011 07:47:26