Hardening and Tempering for the hobbyist

[Chris TickTockParticipant @christicktock]

Hi Guys,

This is the first time I have attempted to harden and temper anything other than a very small item.

I have made 8 punches for staking brass wheels to steel arnours, this includes the punches being usd with a light hammer hitting steel to rivet the wheel on.

My punches are made from 75mm long 9.5mm dia silver steel as that was what i had in my stock.

So my issue is as yet the only heat souce for hardening i have is a plumbers propane torch and this means there is only enough heat source to heat 1/2 inch at a time to bright red needed to quench

So my question is as it is both end of the punch that get hit 9or hit on) is it acceptable or totally not to just heat one end quench then do the other end and quench, then do the tempering of the punch which I am more happy with my method of a uniform heat source?

If this is totally not acceptable any suggested tool / methods please?

Chris

[Chris TickTockParticipant @christicktock]

[not done it yetParticipant @notdoneityet]

Try it and you will see. If you think about it first, you may realise while heating the second end you may be tempering the first.

[Brian HParticipant @brianh50089]

The end that is hit with a hammer is best left soft. If you harden it then small brittle pieces could fly off and cause injury.

Brian

[VicParticipant @vic]

Yes I agree with Brian. When I did my training we were taught never to allow the end of any chisels or punches to mushroom like you so often see. The struck ends had to be ground as required to prevent this. Hardening is not the difficult part provided you have a suitable heat source. It’s the tempering that can be a bit more tricky.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Brian H on 11/12/2019 15:32:57:

The end that is hit with a hammer is best left soft. If you harden it then small brittle pieces could fly off and cause injury.

Brian

+1

I only harden what needs hardening. Hard and brittle often go hand-in-hand, so not good to hammer or snap hardened steel.

This commercial cold-chisel has a hardened tip and soft end. The soft-end has mushroomed out and needs trimming back, but even like that the soft metal is less likely to spray shrapnel about.

For the same reason it's not recommended to bang hammer heads together. As both are hardened, any splinters formed are likely to come off at high-speed. Not funny if a shard goes in your eyes. (Not that hammers are particularly inclined to splinter. I've accidentally clashed them many times without ill-effect. But why risk it…)

Dave

[Chris TickTockParticipant @christicktock]

Thanks Guys, remember my punches are only to be hit with a light hammer.

What I was concerned about was a length of metal having hardness differentials along its length and whether that is an issue. By your posts the answer is not and it is OK just to harden what needs hardening, in this case the punch tip. also it is a fair point heating the other end could and probably does temper the first hardened end, although this is not likely to be too much of an issue.

Chris

[SillyOldDufferModerator @sillyoldduffer]

Posted by Chris TickTock on 11/12/2019 16:32:19:.

…also it is a fair point heating the other end could and probably does temper the first hardened end, although this is not likely to be too much of an issue.

Chris

Um, yeah but no but yeah. The main objection is that any tempering effect is accidental and this flies in the face of heat treating under control to achieve a defined result.

Heating to a particular red-heat temperature and then cooling rapidly aims to capture a particular chemical state inside the steel. Get either temperature or time wrong and the steel won't harden properly or might be burnt.

After successful hardening, tempering relieves strains and improves toughness. It's done at a much lower temperature over a much longer period – the metal takes time to adapt and needs to soak.

In both hardening and tempering, time and temperature are managed for best results. Some steels like HSS are unforgiving if the operator gets it even slightly wrong. Silver-steel is formulated to be straightforward to harden and temper without fuss or elaborate equipment. As such heating the remote end of a hardened silver steel rod might not do much harm or good either way. Might be slightly worse, might be slightly better.

Dave

[HopperParticipant @hopper]

Usually you heat the sharp end of the punch or chisel to cherry red, which is a dark red rather than a bright red (Cherries used to be darker than they are today) then quench the whole thing.

Then play your flame on the punch a half inch or more back from the sharp end until the light straw colour runs up the body of the punch and hits the sharp end then quickly quench again.

The hammer end of the punch is usually left as is, ie soft. You definitely do not want to harden it because as Brian H and SOD said above, tiny hardened shards could fly off when hit with the hammer.

Hardness variations along the body of the punch or chisel are not a worry. They are left as they are. Only the hardness on the cutting/punching edge area is important. The rest of the tool is only there to hold that working edge in place.

BTW do your heat treating in the near- dark, or as dark as possible, to get the best "read" on colours. Doing it under sunlight or bright electric light makes it harder to see the real colour of the steel. And give the punch a clean up with emery paper before hardening and again before tempering so it helps make the colour change more clear.

 

Edited By Hopper on 12/12/2019 00:30:23

[HopperParticipant @hopper]

Posted by SillyOldDuffer on 11/12/2019 15:49:32:

…

(Not that hammers are particularly inclined to splinter. I've accidentally clashed them many times without ill-effect. But why risk it…)

Dave

Exactly. I know guys who claim to have welded petrol tanks many times without steam cleaning and filling with inert gas. Doesn't mean I am about to do it though. One in a thousand? One in a miliion? Makes no difference if you are that one.

[JasonBModerator @jasonb]

One thing Hopper missed off is to clean the metal back to bright after hardening otherwise you won't be able to see the colours when tempering, otherwise I would do it exactly as he has described.

[Author]

Posts