case hardening with ashes from fire

[MattF]

Some tend to dump it straight from the container for quenching, others let it cool then heat & quench later. Regarding tempering, that is one of the reasons for doing it. You can't temper some pieces otherwise.

 

[bill_gj]

Yes. I have no hard theories about post-treatment for case hardening. My reservations are based on the differences in composition and microstructure when you compare heat treatment of an homogenous material to what is effectively a composite - one material for the majority of the structure with a carbon-enriched skin of unknown thickness.

 

[BrokenBiker]

i tend to stick with the method of using tool steel if i need something to tempered after hardening, or if i just want something to resist wear i will use cheaper mild steel and case harden it, for instance i made a sear spring for a mates sidelock shotgun while i was an apprentice and used tool steel, bit the hammer was just case hardened mild as it only needed to be hard

 

[ronan]

Yes. I have no hard theories about post-treatment for case hardening. My reservations are based on the differences in composition and microstructure when you compare heat treatment of an homogenous material to what is effectively a composite - one material for the majority of the structure with a carbon-enriched skin of unknown thickness.

Funny you should say about composite Bill, BSA motorcycles used en32 case hardening steel for some of the gears in their gearboxes back in the 50's. I have seen a lot of these case hardened gears which appear to have the case eroded or broken away from the tough steel core. The material is obviously homogenous , but after case hardening appears to become or behaves like a composite. The americans used this same steel, but called aisi 8620 in their wartime service rifle action, the m1 garand, they however done a triple heat treat and didn't suffer any surface deteriation. What this triple heat treatment entailed i do not know. But it seems the simple quench from high temps wasn't sufficient.

 

[bill_gj]

Brokenbiker & Ronan - exactly so. Case hardening a steel of a 'mild steel' type will give a resistance to wear and that's about it.
If a part is to be used for any purpose other than resisting wear then another base material has to be considered.
Your comment on gears - I've seen a very similar result on camshafts made from chilled cast iron (where you get a grey iron core and a white iron skin). After a lost of use, pieces of the white iron skin flake off. Presumably because the interface between the white and grey irons has fatigued.
And as you say, if a part has to flex a bit, as well as offer a hard wearing surface, then you have to start off with the right stuff in the first place.

 

[graffian]

When I have seen heat treatment described on bike parts it's often along the lines of:
30 thou case
Grain refined
Hardened.

There is no need to anneal as the core isn't hardened.
They clearly didn't do things for fun so I suspect the grain refining is necessary.