Normalizing air hardening steels

H

Heli00

Joined
Oct 19, 2017
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Hi,

Happy New Year !

If I understand correctly, to normalize low hardenability steels, one would heat the steel a little above austenizing temps and then cool in air.

But what about high hardenability steels, like say A2?

It will harden if cooled in air, so I would be quenching, not normalizing it.

Thanks in advance,
Constantin
 
With steels like A2, you're correct. Normalizing or thermal cycling them will harden them. The best way to refine grain, that I know of, on air hardening steels is to use a "prequench". This is a quench that is done 150°-200° (roughly) BELOW your austenitizing temp. This has been shown to refine grain in air hardening tool steels like A2, and especially D2. If your austenitizing temp for A2 is going to be 1775°F, then do a prequench about 1575°F.

Just some terminology FYI.....Normalizing does not refine grain. If anything it grows it. But I think you're actually talking about "thermal cycle", since you said the goal was to refine the grain on the steel you're working with. Normalizing is about 100°F-150°F above aust temp and is used to relieve stress, help distribute carbides, and reset grain structure, and can actually grow grain, depending on the alloying in the steel. When we are trying to refine grain, it's "thermal cycle", and is done right around the austenitizing temp.
 
samuraistuart said:
With steels like A2, you're correct. Normalizing or thermal cycling them will harden them. The best way to refine grain, that I know of, on air hardening steels is to use a "prequench". This is a quench that is done 150°-200° (roughly) BELOW your austenitizing temp. This has been shown to refine grain in air hardening tool steels like A2, and especially D2. If your austenitizing temp for A2 is going to be 1775°F, then do a prequench about 1575°F.

Just some terminology FYI.....Normalizing does not refine grain. If anything it grows it. But I think you're actually talking about "thermal cycle", since you said the goal was to refine the grain on the steel you're working with. Normalizing is about 100°F-150°F above aust temp and is used to relieve stress, help distribute carbides, and reset grain structure, and can actually grow grain, depending on the alloying in the steel. When we are trying to refine grain, it's "thermal cycle", and is done right around the austenitizing temp.
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Thank you, you’re right, great explanation. I thought normalizing also refine grain.
 
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Are prequenches only performed on air hardening steels for grain refinement?

Also, how do you normalize air hardening steels?
EDIT: Looks like you don’t.

Thanks again,
 
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Just wanted to mention that I bought @Larrin book, “Knife Engineering”, hopefully it will answer all my questions and I’m sure it will be a great reference going forward. Should arrive in a few days.

Larrin, thank you for your efforts!

Constantin
 
Larrin's book and website are THE BEST places to go for info on steel and heat treating.

For grain refinement on the low alloy oil quenching steels, thermal cycles are an excellent way to refine grain. Triple quenches also refine grain, but can cause other issues. You can certainly try prequenching low alloy steels. I have done so before, for example in 52100 or O1 etc prequench ~1425°F prior to your final quench. But thermal cycling is the preferred method, at least in my shop.
 
Heli00 said:
Just wanted to mention that I bought @Larrin book, “Knife Engineering”, hopefully it will answer all my questions and I’m sure it will be a great reference going forward. Should arrive in a few days.

Larrin, thank you for your efforts!

Constantin
Click to expand...
What he said.

For 30 something bucks you can get a great answer the is technical but easy to understand. It's pretty awesome to finally have good tested info easily available.

Thanks @Larrin
 
samuraistuart said:
Larrin's book and website are THE BEST places to go for info on steel and heat treating.

For grain refinement on the low alloy oil quenching steels, thermal cycles are an excellent way to refine grain. Triple quenches also refine grain, but can cause other issues. You can certainly try prequenching low alloy steels. I have done so before, for example in 52100 or O1 etc prequench ~1425°F prior to your final quench. But thermal cycling is the preferred method, at least in my shop.
Click to expand...

Could you please explain what thermal cycles are?

Thanks again,
 
Just started looking through the material JTknives JTknives referenced above, enough for weeks and weeks of reading. I was hoping to find more concise answers than just reading through all that right now, you know, an easier way... a glossary of terms in the context of knife making, something more summarized.

I could see that some people tried to bring related information together, etc and thank you for that, but it’s still a big lake of information.

Another week until I receive @Larrin book, oh well...

So, is there a glossary, definition of terms, like what is normalizing, annealing, thermal cycling, etc? As in normalizing is done above austenizing temp and the purpose of it is to achieve this and this, etc. How is it applied to hypereuctoid, etc steels.

Pretty frustrated right now... my apologies.
 
Well, I'll try to make it as simple and quick as I can with my limited knowledge. You can use the custom search engine that is posted in the stickies at the top of Shop Talk.

From hottest to coldest:

Normalizing. Done on oil quenching steels to help relieve stress, particularly forging or grinding stress, it also helps to distribute carbides evenly, particularly after forging, and it evens out the austenite grain size, but can grow grain the grain due to the high heat. This is accomplished by heating to ~150°F above the hardening temperature and let it soak for a period of time. The more alloy in the steel, the more I like to soak. For steels like 1095, short soak, 5 minutes or so. For 52100 I usually do 20 minutes or so. You allow it to air cool, do not quench.

Thermal cycling. Done on oil quenching steels to refine the aus grain. Usually 3 times is good, but more cycles can be used. This is accomplished by heating to around your hardening temperature and allowed to air cool, do not quench. In order for the grain to refine, the phase change must occur, and that is between ~1350°F and ~1414°F. I like to descend thermal cycles. Like 1500°F, then 1475°F, then 1450°F, then 1425°F.

Annealing. This is done to soften the steel for grinding, and can also be used to spheroidize the carbides. The temps and times depend on if the steel is hypoeutectoid (like 5160), eutectoid (like 1080), or hypereutectoid (like 52100). I'll let you search the different annealing techniques for the different types of steels. A LOT to type. Done in the ~1300°F range, but again depending on steel and the exact goal of the anneal, there are others. Like DET anneal, used on hypereutectoids like 52100, hold at 1460°F for 20 minutes and then descend to ~1200°F at a rate of ~600° per hour. But if the steel is hypoeutectoid like 5160, you can heat it up to hardening temp and then stick it in a bucket of ash or vermiculite and let it slow cool overnight. Or if using a forge, heat it up to hardening temp and then turn the forge off and let the blade cool in it.

Hope that helps. That is quick and dirty.
 
samuraistuart said:
Well, I'll try to make it as simple and quick as I can with my limited knowledge. You can use the custom search engine that is posted in the stickies at the top of Shop Talk.

From hottest to coldest:

Normalizing. Done on oil quenching steels to help relieve stress, particularly forging or grinding stress, it also helps to distribute carbides evenly, particularly after forging, and it evens out the austenite grain size, but can grow grain the grain due to the high heat. This is accomplished by heating to ~150°F above the hardening temperature and let it soak for a period of time. The more alloy in the steel, the more I like to soak. For steels like 1095, short soak, 5 minutes or so. For 52100 I usually do 20 minutes or so. You allow it to air cool, do not quench.

Thermal cycling. Done on oil quenching steels to refine the aus grain. Usually 3 times is good, but more cycles can be used. This is accomplished by heating to around your hardening temperature and allowed to air cool, do not quench. In order for the grain to refine, the phase change must occur, and that is between ~1350°F and ~1414°F. I like to descend thermal cycles. Like 1500°F, then 1475°F, then 1450°F, then 1425°F.

Annealing. This is done to soften the steel for grinding, and can also be used to spheroidize the carbides. The temps and times depend on if the steel is hypoeutectoid (like 5160), eutectoid (like 1080), or hypereutectoid (like 52100). I'll let you search the different annealing techniques for the different types of steels. A LOT to type. Done in the ~1300°F range, but again depending on steel and the exact goal of the anneal, there are others. Like DET anneal, used on hypereutectoids like 52100, hold at 1460°F for 20 minutes and then descend to ~1200°F at a rate of ~600° per hour. But if the steel is hypoeutectoid like 5160, you can heat it up to hardening temp and then stick it in a bucket of ash or vermiculite and let it slow cool overnight. Or if using a forge, heat it up to hardening temp and then turn the forge off and let the blade cool in it.

Hope that helps. That is quick and dirty.
Click to expand...

Thank you, great information, I have started to consolidate the info in a document for myself.

Also found the “hottest to coldest” order very informative!
 
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