W-2 and 1075

wmhammond

Well-Known Member
So, I think I have just about boiled it down to using only 2 high carbon steels: W-2 and 1075. I don't have a heat treat oven but I think I have controlling temperature in my forge down to pretty close tolerances using a baffle and a thermocouple. For those of you who do use a heat treat oven, what is your target temperature for each of these steels just before you quench? Also, are there any other nuances that I should be aware of in this process? Thanks,

Wallace
 
so, i think i have just about boiled it down to using only 2 high carbon steels: W-2 and 1075. I don't have a heat treat oven but i think i have controlling temperature in my forge down to pretty close tolerances using a baffle and a thermocouple. For those of you who do use a heat treat oven, what is your target temperature for each of these steels just before you quench? Also, are there any other nuances that i should be aware of in this process? Thanks,

wallace

w-2: 1475f
1075: 1450f-1500f
 
Wow....Kevin's keyboard must have quit working right in the middle of his response! ;) I've never seen a post from Kevin so succinct. :D ;)

Haha...just kidding Kevin.

My response though echoes what Kevin already typed.
 
I love Kevin's answer. If you remember the old joke, "It just don't take him long to look at a horseshoe." One other question: Say you pre-heat your oven to 1475 and you have 3 knives to treat. Once you put 'em in there how long does it take to get them up to 1475 and how do you know? Because once they get to 1475 after that they are soaking and that will just get Kevin and Ed worked up again. Thanks,

Wallace
 
There will be a rebound period as the inside of the oven comes back to temp, that is one indicator, another is if your oven has a view port, when the blades are the same color as the walls of your kiln you are good. If they are prepared well, neither of these steels necessitate a soak, so it may just be a unnecessary use of time and electricity to soak a blade that is already in full austenite solution. If the prior microstructures are relatively fine and easily dissolved you may get some elevated retained austenite with the W-2 with more solution than necessary.
 
If you have a port, stick a telescoping magnet in there. As we know the magnet will no longer stick in the 1414-1425F range. That's not 1475, obviously, but close. I've heard table salt melts right at 1475F. Maybe you could sprinkle some on a blade and watch thru the port as it melts? I would guess 3 minutes tops. When I insert my blades into oven, and after the thermocouple rebound (usually only 15-20 seconds tops), I ADD 2 minutes to my soak time. If I want a 10 minute soak, I do 12 minutes after thermocouple rebound.

Kevin....you're saying W2 does NOT need a soak? Hmmmm Wow. Mandela effect or something going on in my head. Thought W2 needed a short soak (even if prepared correctly from normalizing temps on down and coarse spheroidizing out of the way, and a fine pearlite microstructure), due to the excess carbon beyond the eutectoid.
 
With the elevated carbon content and relatively low V content of W-2, there is not enough complex carbide formation (beyond Fe3C), to keep the carbon out of solution more than a 10XX series. The V is only there to stabilize the grain boundary locations. So you can essentially treat it like a 10XX series steel, but if you over do it and put that proeutectoid carbon into solution you will then have issues. This is primarily a matter of not overheating, especially if you start stripping carbon off the V carbides, which means you really overheated things, but in all things diffusion time equals temperature and oversoaking could pull the easier carbon into play.

Just remember that in the end it all hinges on the microstructure going into that heat and soak. Very fine pearlitic, bainitic, or martensitic structures can often all but eliminate the need for an extended soak, even in alloy steels. But coarser structures, e.g. spheroidal, and full anneals or problematic segregation (such as alloy banding) will always require longer soaks to evenly distribute proper solution even in relatively simple steels. This is why it can be so critical to know the thermal history of the steel you are working with, each heat leading up to that hardening soak will have its effect in determining the outcome.
 
Wow. This WHOLE time I've been soaking W2 for 10-15 minutes. This AFTER normalizing 1650F, air cooling only, thermal cycling down as we do, air cooling only. No anneals, all this done after machining. Matrix should then be fine pearlite....and I am soaking that, and I should NOT be soaking that, huh?

But 52100 and O1 are different stories, or are they? Because of the alloying, the soak is employed, if we're sticking to the 1475F aus temp and starting with fine pearlite as well?

This whole time I've been under the impression that any hyper eutectoid steel should get a soak, if hardening in that sub 1500F range. Even 1095 gets a soak, when maybe it shouldn't (austenitizing a fine pearlite structure). So if one had spheroidized 1095, they normalized and cycled it, air cools, with fine pearlite, and they harden at 1475F with NO soak, what makes that steel any different than 1084? Assume the answer to be the pro-eutectoid cementite left as carbide at 1475F, which gives some added wear resistance over 1084, even tho both steels only have ~0.7% C in solution. Same with W2....the difference is finer possible aus grain (vanadium), a little tougher than 1095 (chromium), and a little extra cementite?

But with O1 and 52100, there is some decent alloying. To have the alloying advantage, one must either use temp or time. Temp being RA problem maker, while time is much less of an RA trouble maker but still gets the alloying advantages.

Does that sound right, or what am I missing? Thank you so much for all your help with this HT stuff, Kevin! Would be nice to buy you a few drinks someday!
 
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Don’t get me wrong, if what you are doing is working, stick with it. There generally is no downside to soaking so long as you have good temperature control and, if you do, the only real threat is that of elevated retained austenite if you oversoak.
There is very little danger posed to eutectoids and hypoeutectoids, the carbon levels will seldom reach problematic solutions for RA. 1095, W-1 and W-2 are the ones that really need temperature control, that proeutectoid cementite will readily dissolve when overheated. 1475F keeps things stable and allows for a short soak.

Alloy steels and tool steels, as you mentioned 52100 and O-1 have much more stable carbides than Fe3C and so are not only safer to soak they need it. Overheating them will put extra carbon in solution at the expense of the Cr carbides, and thus fortifying the austenite on top of the effect of the substitutional atoms that does not go away when the carbide is broken. So longer times, at lower temperatures, is the safer route.

This is where a lot of folks have a hard time wrapping their head around the idea of O-1 not being an easy to heat treat steel versus 10XX. Many makers will solely focus on the quench as the measure of the steals heat treatability. Time, after time, the first thing people will look at in trouble shooting a heat treatment is the quench, when it is actually normally the last thing to be the real problem. Since O-1 will harden in just about any medium (around a 10 second gap to pearlite) its real challenge is in getting proper solution. 10XX series can achieve proper solution quite readily and it really isn’t that difficult to find a faster quenchant to keep that solution for the martensite. So between the two, the greater challenge is proper soak at steady temperature to get the proper solution. 1084 will give you good solution from Ac1 all the way up to the grain coarsening temperature. But O-1 has a narrow range in which it needs to be held in order to obtain proper solution while maintaining abrasion resistant carbides, deviation from this will get you elevated RA and loss of abrasion resistance. If one has an accurate heat source, like a good oven, then almost any steel is available as a good, high quality choice, but most beginners don’t start out with this equipment and so O-1 is not a better choice over a simpler alloy.

The guideline is quite simple and logical- the simpler the steel, the simpler the tools required to work it. With each addition and increase in alloying comes a greater need for better controls.
 
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Thanks so much, Kevin! Nice explanation. I've been giving the O1 and O7 fine spheroidized steels a 20 minute soak....hoping that is long enough without being too excessive. If I understand correctly with long soaks, as long as the Tungsten carbides (some O1 has a touch of Vanadium as well) are not dissolved, which happens at elevated temperatures much higher than even a normalizing heat for O1, then grain growth isn't a concern, but too much carbon in solution/RA will be a concern. My results are good, always shooting for better.......
 
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