Hardening Steel

I have some Fly press punches & matching dies. These were to make a self centering multi size hole punch for my coin rings.

On completion I found I needed to cut a relief at one corner of the dies for the smaller coins. They were very hard & I had to gently grind them. But one particular die was soft & I could turn the edge off in the lathe. This means the die is too soft to have a long life. I have a faint recollection of straw colour but not sure. So how do I harden the die up. I do not know what grade of steel they are made from. Thanks in advance for any help. Some pictures.

Steve.

Do you know what grade of steel they are made from?

OP says he doesn't know what the steel is, so it's a crap shoot.

The standard way to harden high carbon steels is to heat to around 800°C and hold for one hour per inch of thickness. Then quench in brine and agitate while doing so. If you don't agitate you'll end up with a hardness around 40Rc instead of the wanted 65Rc, or thereabouts.

To temper heat to the required temperature (a couple of hundred degrees or so depending upon application) and hold as for hardening and then quench.

Of course one could just heat to red and then piss on it and hope the nitrogen compounds give a form of nitriding!

Andrew

As Andrew says without knowing the steel composition its difficult -- it may be that this die was low carbon steel and case hardened ? In any event the only thing to do is suck it and see !

Treat as suggested by Andrew and you either have a die or you make a new one, assuming it hardens you will need to polish it and temper to pale straw colour in subdued daylight .

John

Heat an offcut to dull red hot and quench in water, if it can still be filed, it is mild steel and only deep case hardening or equivalent would save it for use as a die. The best die steels used to have manganese in the alloy.

That is something I cannot do because I only have the die supplied with the punch. As said all the others are very hard. It was just this one I noticed I could file. I am only punching soft coins & nothing steel. It works but did not think it will have any longevity. So if I am reading correct I will have to hold it at 800c for 1 hr as it is about 1" thick. Then quench in tuna fish brine water,(that's all I have) joke. salt water, Then reheat to straw colour & quench in water, not oil.

Steve.

By the time the hardening process is completed, it would likely be a slightly different size (and shape).

Normally a good quality item would be ground-finished after hardening and tempering.

So does that mean I cannot harden it because it will trash it size wise.

I bought from various sources 2nd hand. They are all pretty old I guess. It's just that I was not aware that hardening changes the shape of it. Thank all for advice anyway.

Steve.

When I was a press tool designer, the default material for pierce/blank dies was BO1, a 'non-shrink oil-hardening' tool steel - so it didn't need a brine-quench. In any case, for largish press dies such a sever quench risked craking, which was why such steels were developed.

Punches would be BD3, a similar material but with extra abrasion resistance.

Buying second-hand is always a risk because of the unknowns. What could possibly do wrong?

• Item is of unknown specification
• Purpose item was made for is unknown
• Item is unfinished or damaged

In this case I guess one of the dies was either cheaply made in the first place (rubbish metal tat is older than Tubal Cain!), or is intended for cutting something soft, such as thin leather. Or it could be a pattern. No-one knows!

Heat treating is a complicated subject, but it relies on knowing what the metal is. Conventionally, one of the higher Carbon Steels, or relative. Then tables showing how hot, for how long, and how to cool it for best results (in water, brine or oil). Rule of thumb one hour at red heat per inch of thickness, and it's safer to cool in oil rather than water (but the result won't be so hard).

Being able to harden and soften metal as required with heat is a handy trick, especially as it works well on cheap carbon steels. Broadly, the technique is to machine the metal whilst it's soft enough to cut, then harden it, and finish off as necessary by grinding. Although the method is still common, Carbon Steel has disadvantages, like rusting. So Carbon Steel has been replaced in many applications by Alloy Steels, which probably won't heat harden or soften in the same way. Knives are a good example: most modern knives are mass-produced by stamping and grinding hard stainless steel to shape, not by forging and heat-treating a carbon steel blade with traditional methods. I could probably forge a home-made knife from an old Flymo blade, but not by recycling new knives from my kitchen.

Dies and punches can be almost anything. Might well be made from a plain heat hardened carbon steel, but there are no guarantees! Industry has been making very hard tough stamps from alloy steels for about a century, and maybe softer ones for special purposes too.

If the specification can't be traced, experiment! But don't draw general conclusions from the result. In this set, it appears one of the dies is an outsider that may not be typical of anything.

By the way, I'm not against buying second-hand at all. It works well enough most of the time. Just buy with eyes wide open and don't make assumptions or expect perfection.

Dave

You may find that even soft they will have a long life, panels for prototype cars were made using a very low melting point alloy and could make around 100 pressings before needing to reform the die. Unless the die is a cutting punch then it could last very well for forming.

Mike

Thank for all the answers & comments. I suppose for what I paid for all of them was not a bad deal. Will stick with it for now. I could make another if it fails from a known steel. The actual size of this one means it will not get a lot of use anyway.

Steve.

A wipe with an oily tissue before use would extend its life, or a wax polish, even.

Strangely, I have a tin of California Carnuba wax that I dab on before every press. Also use it on the coins before folding them. Amazing what a bit of lube does to help. Cheers old mart.

Steve.

A bit of lube works wonders in so many areas.

Mike

Careful.

Steve.