Hardening and tempering

[AHTI123]

I have made a louvre press and also the louvre die (from tool steel) but im assuming i will need to harden the die? It will have to shear/cut the metal as opposed to me slitting the metal first.
Anyone got any tips on the process of hardening (and tempering?).
Thanks

 

[Agroshield]

Anyone got any tips on the process of hardening (and tempering?).

Find the datasheet for the particular tool steel you have used and follow the instructions therein.

If you do not know what tool steel you have used, do some experiments on an offcut (e.g. make a small square punch and die) as that will put you in the right field of air hardening, oil hardening or water hardening.

 

[Screwdriver]

Yes, detail the material and we can all chip in with advice. I assume the critical issue will be to choose the path of least distortion. Or possibly allow some room to manoeuvre during the temper cycle(s).

Typically a toolmaker will finish harden and temper then take to dimension, surface grind etc. Even more typical is the average Joe who will finish the part first, then harden and temper.

It may not be an issue at all depending on the material and more crucially, the shape/thickness of the parts. Stock removal may allow internal stresses to present themselves during heat treat. There is also a process called normalising which may be recommended prior to heat treat, dependant on material etc.

 

[outofthefire]

If it's for a short run for yourself follow the advice above, but if its for any sort of production i'd pay someone to do it right. I harden all our hammers, axes and chisels, but the dies for the scutch combs we make are wire cut and heat treated by a specialist company and even then they don't last for too long before they need a tickle with the surface grinder.

 

[AHTI123]

Thanks, il find the details and post back with more info.

 

[AHTI123]

Here's the data below. Obvious to those who know exactly what it means...but I don't.

The die itself is only 3" long x 1/4" deep, so not very big. I was thinking I'd fix it to its mounting block before hardening? The mounting block is bright mild steel approximately 4"x2"x1".

This is a one off just for me so want to harden it myself.

 

[Morrisman]

Something I learned about hardening years ago: when you quench it you can distort it. And the carefully turned mandrel I dunked in water sideways on came out bent beyond use. Quote logical, thinking about it. It should have been lowered in vertically. Which I did the second time around.

 

[Screwdriver]

Well it is O1 tool steel which is really the most forgiving stuff for the amateur (imho). The "O" tells you it's oil hardening which to the gifted amateur means a bucket of chip fat oil.

It says non distorting but as soon as you start chopping it up it can allow any internal stresses to sort of relax. It will be in an annealed/soft state when you get it so it won't do any harm to put the machined parts through a normalising cycle where you effectively take it to the annealing temperature while bolted to a jig to keep it straight/flat (in your case) but I hesitate to suggest hardening it while bolted to a massive block. You'll stop it from cooling quickly enough to harden.

What you can do is after hardening, bolt it loosely to the jig (just to prepare it) and heat it all up to temper it. While it is tempering and still hot, bolt it down fully flat. Careful not to try and bend it when it is fully hardened, it will be as fragile as glass.

TBH, you're probably going to get good results just by heating it up to hardening temp (bright red/orange/non magnetic etc.) and just lobbing it into a bucket of oil. I temper mine in the oven and have been quite lucky with O1 and not had any issues with distortion.

 

[AHTI123]

Thanks for the replies. To recap/clarify.



Do I need to buy an infrared thermometer thing to measure the temp or is waiting (as you've said above) until it goes non magnetic acurate enough for my purpose?
So once upto temp, quench in oil, (until cool??)
Then put in oven at 150'c for an hour, then cool naturally??

 

[Screwdriver]

Infrared thermometer won't work at the temperatures you need, not the cheapo ones anyway. Well, mine doesn't.

Ideally you want a temperature controlled oven because the time during which it sits at the hardening temp is also a factor. If you don't have an oven then the process is always going to be hit and miss. I use a magnet to make sure the temperature goes above non magnetic, different materials behave differently so even non mag is a sort of rule of thumb because the curie point is not the same as the hardening temperature but it's close enough.

Colour (black body radiation) is perhaps the best bet for the amateur and there are various charts which show you exactly what colour relates to a given temperature. Get it a consistent bright orange all over and I find that's usually going to work.

150ºC will give it a very mild temper and leave it quite hard so I don't know what's best for your application. Again though, tempering produces a thin oxide on the surface which causes an apparent colour change precisely matching the temperature of the tempering process. Light straw for a hard blade, blue for a "spring temper" etc.

It's all fascinating to me and great fun too...

 

[AHTI123]

Thanks for the info, il give it a go and see how I get on.

 

[outofthefire]

Sprinkle salt on the steel while you're heating it up, when it melts drop it in the oil, salt melts at 801 degrees c. The non magnetic thing works, but the colour red that indicates when the steel loses his magnetism takes practice and a consistent light (ideally darkish). The tempering is going to be a gamble, too hard and it'll chip and crack too soft and it'll deform, unless someone knows better I'd stick it in your oven at it's hottest temperature for a couple of hours better a bit soft than too hard you can always anneal it, normalise it and harden it again if needs be.

 

[pedrobedro]

O1 heat to cherry (it doesn't need to be bright red) then test with a magnet (non mag) and quench in oil. I use an old bean can for small parts with some nondescript engine oil in it. Immerse it totally and don't swish it round then take it out and test it with a file, it should skid over the surface and not dig in. Temper at 220 or whatever your oven will go up to for an hour.