A couple Qs re dies and hardening

[J Tiers]

I decided to try making a die, partly because I needed a particular one. It is a 4-48, obviously standard, but not in stock locally at my local tool joint, and I didn't want to wait for it.

I had recently picked up a considerable amount of what appears to be mostly A2 tool steel. I say "appears to be" because it was all together, and everything that has a mark indicates A2. Of course I can't prove it for any, except those where the wrapper is still un-opened.

Anyway, I made the die, as far as the machining, and went to harden it. Having looked up the A2 info, I determined that I didn't have what seemed to be needed to do the job (air blast, temp controlled furnace, etc), so I decided to use the advice in the recent article on die-making, and simply heat and water quench, drawing back to a straw as a temper.

I also figured that if it turned out to be W-1 or O-1, I'd be doing the right thing anyway.

So, I got it up to a nice bright orange, as hot as I could get it, and dunked it, as usual.

Surprise...... it wasn't hard.....! it was a little hardened, but still quite file cuttable.

So, I said a few unprintable things, and thought a while. I considered what it might be, decided it for sure isn't O-1 or W-1, might be CRS, etc.

Being stubborn, I decided to have another try.

This time I was persistent, and decided to hold it in the flame longer, in case it could get any hotter. As far as I can tell from color, it was not one iota hotter, although I held it in there quite a while. Same orange color.

Side note: Since the whole die is only 0.640 diameter and 0.250 thick, it was hot right through even the first time..... So no cold spots that didn't get to hardening temps.

So I dunked it anyway. Same quench process.

This time, it came out hard enough that a file could not bite on it.... glass hard. So I drew it back to a straw color, heating it on a small metal plate for even heating.

Aside from a difficulty starting the die, due to inability to grind a good start, it seems to work OK, although it isn't entirely pretty.

Anyhow......... Does the apparent need to soak longer at temperature indicate that it really may be A-2?

Most of the A-2 instructions indicate a need to soak a while, although I didn't quite get to the times recommended.

I know that regular W-1 or O-1 would have been hard if quenched directly as soon as they reached the proper temp. I never have any trouble hardening those.

So I am thinking that the soak time requirement may be an identifier than this stuff really IS A-2.

Thoughts?

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BTW, yes, this is a case of spending $40 time to make a $8 item. But I just wanted to do it, OK?

[hoss2006]

A2 is Air hardening. O1 is oil hardening.
I make trim tools all the time at work using A2 and O1.
We do use an oven though.
Typically for A2, the part is wrapped in stainless steel foil, then heated to 1750-1800 degrees F. (bright orange color)
It soaks at that temp for 20 minutes per inch of thickness.
Then is removed and cools in the ambient air.
Once it cools enough that it can be handled by hand, it's unwrapped and placed in the oven
at 500 degrees F for one hour to draw back(straw to light purple color).
This gives it a Rockwell hardness of around 60.
Lower drawback temps will give a harder Rockwell.
We use this for the main cutters.

O1 is heated to 1450-1500 deg F (orange color) for 20 min per inch then immersed in oil.
Once it cools to 100-200 F, it's cleaned off then placed in an oven at 450 deg F for one hour.
this draws it back to about 60 Rockwell. (purple color if you sanded off some of the oil black to see beforehand)
650 deg F drawback will give about 52-54 Rockwell.
Water never enters the picture.
I've made hundreds of punches and cutters but never a die but 60 Rockwell is
very tough(file will just bounce off) so it should work.
Hoss

[dalee100]

Hi,

Yep, next time bring your A2 to temp and hold as needed. Then just remove from heat and set in a non-drafty place and just walk away. One thing about it, you'll know if it isn't A2, it'll still be soft when it cools .

I'm pretty surprised that you didn't twist or crack your die all out of shape, (so to speak), by spanking it that hard with water. Heat treatment is one area that you really need to know what kind of steel you have. If you expect to get the not only the best results, but even just usable results.

As far as the $40 worth of time and materials vs. an $8 dollar tool. Well, what real man-machinist among us wouldn't have done the same thing ! I think it's a part of the disease/mind set of being a machinist.

dalee

[J Tiers]

The die is so small, only 0.640 x 0.25, that's probably why it didn't warp. That and being dunked face-on. Warping seems to be related to uneven cooling rate, but a small compact piece seems to be relatively insensitive to warp.

if it was long and uneven in size, I can see it warping a lot more if cooled from one side when dunked. lengthwise would be better then.

I was under the assumption that air-blast was needed to cool rapidly enough, even though the material is "air hardening". Possibly that is for a lot larger item that would otherwise lose heat only slowly?

The small part does cool pretty fast in air, still takes a little time. Certainly not enough to harden O-1 etc much. So if it hardens OK in air cooling it has to be A-2 or the like.

[Mac1]

so I decided to use the advice in the recent article on die-making, and simply heat and water quench, drawing back to a straw as a temper.

Are you sure the article said to water quench? I've read it a couple of times and it appears he simply lets it air cool for hardening.
I am referenceing Jan-Feb HSM article "Making miniature taps and dies"

[Benesesso]

A steel like A2 has a lot of its carbon tied up with all that Cr and Mo as carbides. Carbides resist breaking down under heat, and that's why the soaking time at temp, plus the high temps, are required to make it hard. The cooling rate for A2 isn't very important for hardness--but too fast and it cracks, especially at sudden changes in thickness, etc.

[J Tiers]

May not have been that article, I did see it somewhere recently. But in any case, I didn't know for sure what I had..... not having tried air-cooling on a sample, so it made sense.

Turns out water cooling was better anyway.

I did try air cooling since, using a no-good die attempt, and it got pretty hard cooling in air, assuming that a re-heat and short soak actually removed the hardness prior to cooling.... Some of the air-hardening steels can be tempered at 1000F and still are hard.

I did notice that the surface scaled a LOT more with air cooling. Huge peeling flakes of oxidation. NOT practical to do air cooled unprotected.

With the water cooling there was hardly any time for oxidation, since I had it in a reducing flame area and dropped it straight in. No flaking.

The slightly less hardness seems to be a surface decarb type deal. The bright but softer surface can be removed, leaving a hard surface under. I attribute that also to the air cooling.

I don't have any toolwrap, nor do I have ready any containers. This torch probably wouldn't heat a larger container hot enough without setting up a firebrick enclosure. Probably would need a larger torch.

So for now, I plan to keep water cooling if I do any more.

[J Tiers]

Are you sure the article said to water quench? I've read it a couple of times and it appears he simply lets it air cool for hardening.
I am referenceing Jan-Feb HSM article "Making miniature taps and dies"

Incidentally, on page 10 of the magazine, the author mentions that he sometimes uses water quench "even with A-2" "Even though it may or may not have any effect on the hardening process".

So I guess it WAS that article.


Just for grins, here is the more photogenic of the two dies.... This one wasn't hard enough, which I discovered while using it...... The threads got a bit mangled by the work, which wasn't fully soft itself.



The next one I used smaller holes on, and it didn't look anything like this nice, downright ugly, in fact, but on the other hand, it cut the thread.........

[Your Old Dog]

I don't have any toolwrap, nor do I have ready any containers. This torch probably wouldn't heat a larger container hot enough without setting up a firebrick enclosure. Probably would need a larger torch.

So for now, I plan to keep water cooling if I do any more.

You can dunk it in carbon putty from the welding supply and if I'm not mistaken, you can use Lamp Black from the masonry supply to keep the carburization down. When I made my engraving chisels from S5 I heat soaked about 3 minutes (15 min per 1" cross section) as I was only interested in the tip and not the shank. The carbon putty worked pretty well. I've also heard you can use common liquid soap to do pretty much the same thing. I'd only use stainless foil with an oven. Don't think it would work all that well with a torch.

[J Tiers]

The article suggested a small closed tube for taps, Dunno what for dies, I have a couple small turned containers that would probably seal, and fit a small die. But I need to work on them a bit.