52100 heat treat questions

jaxxas

Well-Known Member
I have just heat treated my first (using stock removal) blank, 52100. I only have the Rockwell files, but it seems to come out fine except for some warping. As hardened the 65 file would barely scratch it, and after tempering it is somewhere between 55 and 60 rockwell. I quenched in canola oil at about 125-130 degrees F. So I guess I'm fairly happy with that but I came up with a few questions.

Not really sure why the blank warped, I cut out the shape rough on the bandsaw, drilled a few holes and ground to near final dimensions. Is the best attempt to straighten the blank to retemper and try to straighten the blank while hot?

I followed the heat treat program at this link
, and my question is, if I'm doing the stock removal method do I need to do the normalizing and spheroidize anneal? I have the impression that these steps would be necessary after forging? If it matters I got my 52100 from New Jersey Steel Baron which I understand ships annealed.

The blank developed quite a bit of scale during hardening, would you generally wrap 52100 with stainless foil before hardening? Because of the chromium? If wrapping in stainless foil would you add a few small wood chips?

From what I've read I understand that generally you want to temper ASAP after hardening once the blank gets to or near ambient temp. It takes nearly 2 hours for my oven to cool down to tempering temps. Is waiting 2 hours to temper an issue?

TIA
 
I'll try to help.

1. 52100 from Aldo comes heavily spheroidized (annealed). You likely will not achieve max hardness (67+) with Aldo's steel without a normalizing. Yes, normalizing is a must after forging, but for stock removal not always necessary. However, this particular 52100 from Aldo needs it. 52100 from Alpha Knife, after talking with Chuck and others, does not need it. The good thing about normalizing, it will wipe out any stress in the steel as well (help correct warping), as long as your grinds are pretty even. To normalize 52100, 1650f for 10 minutes, air cool. This normalizes the steel, sets up the carbides, but at the expense of possible aus grain growth. To take care of aus grain after normalizing, thermal cycle the steel a few times. Bring up to past non magnetic (1475 is good temp), let it soak a minute or two, air cool. Do this three times. Now you are ready to harden. 1475f for 10 minutes, quench in 130f canola or commercial oil. There is no need to re-anneal the steel after you've normalized and thermal cycled it, unless you wanted to do some drilling or more machining. In that case, after the final thermal cycle of 1475f air cool, do one more, but instead of air cool, quench it. Then place in oven at 1200f for an hour or two. This will soften the steel very well for easy drilling/machining. Usually, my blank is ready to go, bevels cut, edge at .020" or so, ready to harden. I always normalize and thermal cycle my steels before hardening, that way I know exactly what condition they are in going into austenitizing.

2. In case a warp does occur, you can take care of that during the cool down after quench. Between 900-400f the blade is silly easy to bend with a gloved hand(s). Once 400f is reached, you'll notice the blade will start to stiffen up and not bend...this is the martensite forming. Once you get down to 200f or so...it's set. You can also straighten during the tempering process. Search the 3 point clamp method for straightening blades during temper. It seems to not work under 400f tho. If you want a very hard blade for kitchen use, try to do any needed straightening during the cool down, not the temper method. There are other ways to straighten blades. Bead blasting the concave side (I think it's the concave side) seems to work. Search that one too, if interested. If you have a steel that you're not normalizing, like O1 for instance that is stock removal, then an hour at 1200f will help stress relieve.

3. One point about the link you provided and the hardening temp....we're trying to make a knife, not a ball bearing. So stick with 1475f as your austenitizing temp using 130f canola. Don't go above 1475f. 1550f will give you larger carbides, not really what we want with 52100 and a knife edge.

4. You do not use foil for 52100, especially during the hardening procedure. Scale isn't really a problem....it's the decarb layer that is a problem. You can use foil for the normalizing and thermal cycling, because you're allowing the blade to cool in still air, still if using foil for this I would remove it and let the blade cool...in still air. For hardening, you can't get the foil off fast enough. It needs to go into the quench ASAP, no foil. Foil is best for air hardening steels like stainless. To control decarb in a kiln, you should use anti scale compound....like ATP 641 or PCB compound. Satanite works so so for decarb layer. Scale is the carbon from the decarb layer. Scale comes off with vinegar and scrubbing, decarb must be sanded out.

5. Yes, generally you want to temper as soon as it gets to room temp or just above. If your kiln is your only source I understand, kilns take a long time to cool down to tempering temps. Is there not way to use your kitchen oven? Our kitchen oven holds a temperature very well, and very accurately (or is that precisely?), checked and re-checked with various thermometers. And it really holds a temp well with a big ole piece of stone cookware to act as a heat sink. Some use toaster ovens to temper, you make look into that as well if you can't use the kitchen oven.
 
Thank you for the reply samuraistuart!

1. I will try your recipe today hopefully! It is definitely a lot less oven time and a lot less heat in my small shop in So. Arizona, particularly this time of year. Just an FYI I haven't ground the bevels yet, I figured I would have less chance of warpage if I did it after heat treat though I know it will be tougher to grind.

2. I will try the glove (hand) method of straightening today as well. Can I assume that I could also attempt to straighten the blank during any of the thermal cycles as well? I'm also in process of fabbing up a 3 point bending setup for my arbor press, so that may be an option too.

3. Excellent point! I confess I was looking for "do all" recipe when I found that pdf. If nothing else I thought it might be a good starting point.

4. Good info on the foil. I'm guess I was fairly ignorant of the difference between scale and decarb. The greyish 'scale' flaked off fairly easily, however the darker black coating will definitely need to be sanded. I will look into getting some anti-scale.

5. Yes I have both a toaster oven and a kitchen oven available, didn't occur to me to utilize them! I need to figure out accurate temps for those before I try tempering in them. I do have a couple of thermometers just need to figure out a way to calibrate the temps. I have a big old bread/pizza stone in the kitchen oven too.

I will definitely be giving all your advice a work out here in the next day or so and I will post back with my results.

Thank you very much for your help!:thumbup:
 
Hey, anytime I can help I will. Just a disclaimer...I learn from reading Verhoeven and asking questions to metallurgists. I have a few years experience heat treating and knife making. Please don't take anything I say as solid, but verify verify verify.
1. yes, grinding post heat treat eliminates some problems, creates others (watch the heat especially towards the edge!)
2. no need to straighten during normalizing or thermal cycling. if a warp will occur, it's most likely to happen during quench. if you see warp during thermal cycling...I myself don't worry about it. After quench is when I take care of any warps, or with the 3 point method during tempering. It would tick me off to straighten on the last cycle, only to have it bend during the quench!
3. recipes are good, but it's best to know why instead of how
4. indeed scale and decarb are different. When the steel is going thru phase changes, the carbon comes out of the steel (decarb layer), and deposits on top as a layer of scale. The decarb layer should be sanded thru to hard steel.
5. good job....test that oven with a few thermometers and make sure it's accurate. Test it at different temps! 350f readout on my oven is 350. 400f readout is actually 390f. 450f is actually about 438f. USE THAT STONE!
 
here is some better information for 52100 blade heat treat from Kevin Cashen http://www.cashenblades.com/steel/52100.html. here is a good start on the whys of heat treat from this forum http://knifedogs.com/showthread.php?22568-Your-Heat-Treating-Tool-Box. to check thermometers and thermocouples, buy a few Tempilstik temperature crayons. get one in the 300s and one 1200-1500. i temper in a toaster oven, i have a large pan that i have filled with playsand. bury the knife in the sand, temp seems to stay constant and not spike.
 
Not really sure why the blank warped, I cut out the shape rough on the bandsaw, drilled a few holes and ground to near final dimensions.

Based on my experiences, I think its very likely that a big reason you got warpage is because you ground the blade too close to finished prior to heat treat. Back when I first started using 52100, I had the same issues, and solved it by only grinding to 50-75% prior to heat treating.

Another thing to keep in mind when heat treating blades...... ALL of the spec sheets and other heat treat information that is publicly/commonly available should ONLY be used as a starting point. The reason being is that the published heat treat data is almost always based on a 1" cross section of the given steel. What that means is the recommended heat treat is based on a MINIMUM of a 1" cube of the specific steel type. The only way I know how to phrase it is..... I've never created a knife blade that is 1" thick....and there IS a difference in how a thinner cross section should be handled/treated. That information is based on over 30 years of experience with heat treating 52100. Use the published heat treat information as a starting point, then "tweak" how you do things from there until you get the results you're comfortable with.
 
Thanks again for the help, I understand I have a lot to learn!

1 I have a kool mist setup to help with the grinding heat, but I will watch it.
2 Understood, I meant because mine was already warped.
3 Good info, I am trying to wrap my head around this!
4 Is there a chance I'm going to lose too much carbon?
5 I think I have the oven temp conversion down. I used a small pan of peanut oil and 3 different fryer thermometers. Seems 385 F on my oven is 400 F. That is using the stone as well.

So since my last post, I went through the entire heat treat process again using your "recipe". Tempering in the oven. Using the files I'm still about 65 RC after hardening and 60 after tempering. I was able to sorta straighten the blade by hand but not entirely, certainly not as flat as I think it should be. Even using my 'new' 3 point arbor press bending setup while hot I was unable to get it right.

There was still quite a bit of scale and some decarb after heat treat. The decarb looks deep, I guessing after the fact that I should have sanded the decarb down before my second heat treat attempt!? I've ordered some PCB and some ATP 641 for my next learning experience. Should be delivered this week and I will make another attempt this weekend.

As I was unhappy with the blade flatness, I did the anneal at 1200 F for 2 hours and the steel was silly soft afterwards. It was a good experience seeing the difference in the steel after each process. While annealed I have been able to get the blade fairly flat. Maybe a little more work with that!? I'm assuming I want it perfectly flat on my granite slab?

So I'm pleased that the hardening and tempering seems to be working. Be nice to know with a little more precision. While the blade was hardened and tempered there was no tweak bending possible with what I deemed as acceptable force. Maybe I should force it to the next level just for the learning experience? Obviously I have a ways to go to refine the overall process.

So another question is, how many times can I take the same piece of steel through this process? Am I losing too much carbon?

Thank you for your input samuraistuart, no worries on the disclaimer, I take full responsibility! :what!:



Hey, anytime I can help I will. Just a disclaimer...I learn from reading Verhoeven and asking questions to metallurgists. I have a few years experience heat treating and knife making. Please don't take anything I say as solid, but verify verify verify.
1. yes, grinding post heat treat eliminates some problems, creates others (watch the heat especially towards the edge!)
2. no need to straighten during normalizing or thermal cycling. if a warp will occur, it's most likely to happen during quench. if you see warp during thermal cycling...I myself don't worry about it. After quench is when I take care of any warps, or with the 3 point method during tempering. It would tick me off to straighten on the last cycle, only to have it bend during the quench!
3. recipes are good, but it's best to know why instead of how
4. indeed scale and decarb are different. When the steel is going thru phase changes, the carbon comes out of the steel (decarb layer), and deposits on top as a layer of scale. The decarb layer should be sanded thru to hard steel.
5. good job....test that oven with a few thermometers and make sure it's accurate. Test it at different temps! 350f readout on my oven is 350. 400f readout is actually 390f. 450f is actually about 438f. USE THAT STONE!
 
Thanks Scott, those are excellent suggestions. I'll order up some Tempilstik ASAP. Love the sand idea! I do want to use my toaster oven, just to keep the heat out of the kitchen.
 
Ed,

Actually I haven't ground the bevels at all yet. I ground the knife outline shape near to finish though. So I was and still remained baffled.

Good info on the experience level. I'm pushing 60, so I can only hope to gain 30 years of experience in my lifetime. But I love the fact that the members here are so helpful! I did use those aforementioned specs as a starting point, but I think they were way off the mark.

Thanks!
 
What was the blade thickness when you heat treated? Generally I see warpage with anything less the about .200"
 
That's likely the issue. A rule of thumb in my shop is nothing get heat treated that's less then .125" thick. For those that are planned to end up thinner, the get heat treated, then thinned down to final thickness.
 
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