Importance of thermocycling vs austenitizing in 52100?

L

Leon Husock

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Jul 17, 2019
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Basically what I'm wondering is, are the 10-20 minute soaks at specific temperatures which are generally recommended for thermocycling 52100 as important as the 10-20 minute soak prior to quenching? I'm heat treating in a barrel furnace, which is able to get pretty precise temperatures but has no digital control and so adjusting the temperature is a bit of a pain. If I could get comparable results by normalizing in a forge followed by a vermiculite anneal and then do my actual austenitizing in the barrel furnace it would make the whole process a hell of a lot easier.

Edit: this is for forged blades, not stock removal.
 
Seedy Lot said:
knifesteelnerds.com

How to Heat Treat 52100 - Knife Steel Nerds

Toughness experiments with 52100 steel have resulted in a recommendation for achieving the optimal hardness-toughness balance with this steel.
knifesteelnerds.com knifesteelnerds.com
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Yep, I did read that. The problem is (unless I missed something in the more technical language because I'm not a metallurgist) Dr. Thomas recommends the best procedure for heat treatment that he knows, and what I'm wondering is whether a slightly lazier heat treat will result in a significantly sub-par result or whether I'll get, say, 90% of the quality out of the steel. It's just hard and uses a lot of propane to run a barrel furnace at 1700 for 20 minutes, 1600 for 30 minutes, 1460 for 30 minutes, then turn it off and reheat it later that day/the next day for the actual quench.
 
For the normalizing heat, I think a solid 10 minute hold at temp would suffice, since you have already broken up any possible coarse spheroidite during forging. For the thermal cycle(s), get it up to ~1500°F and hold for a few minutes.
 
DevinT said:
It’s very important to do the proper thermocycling after forging.

Temperature control is the most important.

Be careful you don’t fall into the barely adequate heat treatment. Heat treating is the most important step in knife making.

Hoss
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Gotcha. Sounds like I'll just have to heat my barrel furnace up twice. Ah, well.
 
I have ran multiple batches of 52100 and never quite reached the hardness numbers I was expecting so last batch I used Larrin's pain in the ass process and was rewarded with a couple points higher rockwell using same steel and same oven temp.
 
Seedy Lot said:
I have ran multiple batches of 52100 and never quite reached the hardness numbers I was expecting so last batch I used Larrin's pain in the ass process and was rewarded with a couple points higher rockwell using same steel and same oven temp.
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Well all I've got is hardness testing files so I can't be too accurate, but that's a pretty compelling argument. I'm probably letting things cool in the vermiculite longer than they have to anyway; maybe I can get away with firing the barrel back up later that day instead of annealing overnight.
 
TheEdge01 said:
Is thermocycling 52100 important if you make a blade via stock removal???
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While many knifemakers feel cycling is necessary for grain refinement, that is not really the goal. The difference between heat treating "as-received" material from the factory and steel that you cycled yourself is that the prior microstructure is different going into the austenitize and quench. The carbides are coarser and respond differently during the high temperature before quenching. That isn't always a bad thing. In some cases you can make improvements by having a finer carbide structure. But either way the final austenitize and quench is somewhat different. In other words, the optimum austenitizing temperature may be shifted down somewhat from the finer structure, soak times don't have to be as long (though soaking longer usually doesn't hurt), and the resulting hardness may be higher.
 
Depends on where you get the barstock from. Some places may sell highly spheroidized and need some extra treatment to get the best out of heat treating.
 
Larrin said:
While many knifemakers feel cycling is necessary for grain refinement, that is not really the goal. The difference between heat treating "as-received" material from the factory and steel that you cycled yourself is that the prior microstructure is different going into the austenitize and quench. The carbides are coarser and respond differently during the high temperature before quenching. That isn't always a bad thing. In some cases you can make improvements by having a finer carbide structure. But either way the final austenitize and quench is somewhat different. In other words, the optimum austenitizing temperature may be shifted down somewhat from the finer structure, soak times don't have to be as long (though soaking longer usually doesn't hurt), and the resulting hardness may be higher.
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Thank you!!!
 
Taz said:
Depends on where you get the barstock from. Some places may sell highly spheroidized and need some extra treatment to get the best out of heat treating.
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Most of my steel comes from AKS or USA Knifemaker.
 
I was wondering if those of you familiar with 52100 and Larrin’s DET annealing method could give me some advice? I’m just getting into heat treating myself after a batch of blades were ruined sending them in to have them professionally heat treated. I’m using 5/32” 52100 for stock removal from Pop’s (spherodized annealed). I’m using a kiln to thermal cycle the knives using Larrin’s recommendations at the end of the above linked article to get the DET anneal. I use NuScale 2000 on the blades everytime they go into the oven, and I grind down to shiny steel after quenching to remove any possible decarb or scale. I don’t have access to a Rockwell tester though so I have a couple other methods I use to compare hardness to finished blades that are around 61 HRC. I’m quenching in new #50 quench oil between 70F and 90F.

So the crux of the problem is that using the DET annealing method I cannot get the blades to harden as much as I can when I don’t thermal cycle. If I quench as received steel at 1475 it hardens very well and appears similar in hardness to my “standard”. I’ve tried quenching at 1512, 1525, and 1550 and have yet to get the same type of hardness.

From what I’ve been reading it sounds like the finer the grain structure the higher the austenitizing temperature? I’m not sure if I just need to keep going higher? I appreciate any advice you all may have and if you see this Larrin thank you for all the work you’ve put into helping us knuckle draggers make good knives!
 
Seedy Lot said:
I am a stock removal guy buying from a supplier saying that the steel does not need any extra steps. Without Larrin's method I was getting 60 Rc. After a full Larrin method with same steel, austenitizing and temper I get 63 Rc.
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That’s awesome! Do you mind if I ask what your austenitizing temperature and temper were?
 
Badlands Rifleman said:
I was wondering if those of you familiar with 52100 and Larrin’s DET annealing method could give me some advice? I’m just getting into heat treating myself after a batch of blades were ruined sending them in to have them professionally heat treated. I’m using 5/32” 52100 for stock removal from Pop’s (spherodized annealed). I’m using a kiln to thermal cycle the knives using Larrin’s recommendations at the end of the above linked article to get the DET anneal. I use NuScale 2000 on the blades everytime they go into the oven, and I grind down to shiny steel after quenching to remove any possible decarb or scale. I don’t have access to a Rockwell tester though so I have a couple other methods I use to compare hardness to finished blades that are around 61 HRC. I’m quenching in new #50 quench oil between 70F and 90F.

So the crux of the problem is that using the DET annealing method I cannot get the blades to harden as much as I can when I don’t thermal cycle. If I quench as received steel at 1475 it hardens very well and appears similar in hardness to my “standard”. I’ve tried quenching at 1512, 1525, and 1550 and have yet to get the same type of hardness.

From what I’ve been reading it sounds like the finer the grain structure the higher the austenitizing temperature? I’m not sure if I just need to keep going higher? I appreciate any advice you all may have and if you see this Larrin thank you for all the work you’ve put into helping us knuckle draggers make good knives!
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Sounds like a decarb problem. You need to grind down to a deeper layer of steel to remove the increased decarb then "test". Use stainless heat treatment foil for cycling. All of the clays break down upon cooling requiring you to clean and reapply after cooling between cycles for less decarb.

So using clay does not rule out decarb.

It's difficult to quantify exact hardness numbers without a hardness tester.
 
I’ve been grinding it down prior to testing and I believe I’m getting through any decarb. I’ve ran samples both with anti scale and without and there’s a definite difference when I don’t use it.
 
Last edited:
DeadboxHero said:
Sounds like a decarb problem. You need to grind down to a deeper layer of steel to remove the increased decarb then "test". Use stainless heat treatment foil for cycling. All of the clays break down upon cooling requiring you to clean and reapply after cooling between cycles for less decarb.

So using clay does not rule out decarb.

It's difficult to quantify exact hardness numbers without a hardness tester.
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This is the fourth or fifth piece of 52100 steel that has gone through thermal cycling in the same envelope, ordinary sheet metal with a thickness of 0.4 mm . Stainless heat treatment foil would cost me more then 52100 steel cost :)

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DeadboxHero said:
Sounds like a decarb problem. You need to grind down to a deeper layer of steel to remove the increased decarb then "test". Use stainless heat treatment foil for cycling. All of the clays break down upon cooling requiring you to clean and reapply after cooling between cycles for less decarb.

So using clay does not rule out decarb.

It's difficult to quantify exact hardness numbers without a hardness tester.
Click to expand...
So I’m hardening more coupons tonight and grinding them way deeper. I’m actually looking at the sparks being thrown while I’m grinding them. It goes from no sparks to lots of sparks the more I grind. The best thing is that these are all getting hard and they all were DET annealed. What a rookie mistake thinking that the clay would stop all decarb. The more I thought about what you said the more it was making sense. So far it’s looking like 1500 austenitize for 15 minutes is the hardest quench.
 
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