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I did a search but found nothing useful. I have been reading that most guys do at least 2 tempers and that's my plan. I am wondering if the time between the two tempers is critical.
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Time between tempers
- Thread starter swingline327
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I finish temper #1 - quench - and start temper #2.
Quench at the end of temper #2 and start to work on it.
Quench at the end of temper #2 and start to work on it.
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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The time only needs to be a cooling period. Fast cooling in running water or duking in the slack tub is the best method. Slow cooling in air is actually not as desirable. I just take out of the oven, run cold water over the blade for a minute, and sick right back in the oven. After the second temper, I cool in water again.
The main reason behind the choice to perform 2 tempers instead of one (i.e. double the temper time) is that during the cooling after the first temper there is the possibility to have the conversion of the retained austenite leftovers into fresh martensite...that needs to be tempered as well.
Knowing this appears evident that we need to cool the blade after the first temper and proceed with the second as soon as possible, even if the risk of cracking is unlikely to happen due to the minimal amounts of fresh martensite.
Knowing this appears evident that we need to cool the blade after the first temper and proceed with the second as soon as possible, even if the risk of cracking is unlikely to happen due to the minimal amounts of fresh martensite.
Learn something new every day. Thanks.
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After cooling/quenching the first temper can you wait for say several hours or overnight for the second temper or must you throw it right back in the oven?
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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Yes, it would be OK.
Metallurgically, it is better to do the second immediately, but the amount of RA and the amount of untampered martensite are quite low after the first temper. It would take a lab to detect any difference if there was a 12-16 hour delay....if there was any difference at all.
Metallurgically, it is better to do the second immediately, but the amount of RA and the amount of untampered martensite are quite low after the first temper. It would take a lab to detect any difference if there was a 12-16 hour delay....if there was any difference at all.
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Out of curiosity, what is going on in the steel over time, that makes it better to temper right away vs doing it later?
Also, and this is my main question, I'm curios if the temper process I've been using sounds good or if it needs tweaking. I've been doing this with 52100 and 1084.
1. Temper at 400° F. for 2 hours.
2. Quench in running tap water until cool.
3. Soak in ice water (HEAVY on the ice) for 5 - 10 min. or so just to make sure that the center of the blade has gotten plenty cold and any metallurgic changes have happened all the way through the blade.
4. Repeat 1 & 2.
Also, and this is my main question, I'm curios if the temper process I've been using sounds good or if it needs tweaking. I've been doing this with 52100 and 1084.
1. Temper at 400° F. for 2 hours.
2. Quench in running tap water until cool.
3. Soak in ice water (HEAVY on the ice) for 5 - 10 min. or so just to make sure that the center of the blade has gotten plenty cold and any metallurgic changes have happened all the way through the blade.
4. Repeat 1 & 2.
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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Knifemaker / Craftsman / Service Provider
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- Aug 20, 2004
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There is no need to soak in ice water. Running cold tap water for 30 seconds will drop the blade to room temperature. If you can hold it in your hand and it isn't warm, it is ready to go back in the oven.
With 52100, using two hour long soaks is a good. Simpler steels do fine with one hour soaks.
What can happen during a slow cooling is that any RA could stabilize. There is some issue with the newly created untempered martensite not being stable, but the RA is mostly it.
This is really more of a theoretical metallurgical discussion that a real world concern. As I regularly state, you will never be able to tell the difference. A laboratory might be able to tell....might! As far as blade quality and hardness, it won't matter if you cool it slow for an hour, wait overnight, or plunge it into ice water, between the tempers.
We are talking about single digit RA% in most carbon knife steels, and the cooling rate between tempers making a difference of a few hundredths of a % increase of that small percentage of RA. Without an x-ray diffraction or SEM in your shop, it would be hard for anyone to accurately detect.
As an example, lets assume that a blade had 10% RA ( which is probably much higher than it really would be if properly quenched). If a slow cooling rate between tempers increases that 10%, the final Ra would now be 11%. In actuality, it is more likely the difference would be 5% vs 5.05%. And even this small amount of RA would be reduced in the second temper.
On steels with high RA amounts, a third temper is useful, but there is a diminishing return after the second temper.
With 52100, using two hour long soaks is a good. Simpler steels do fine with one hour soaks.
What can happen during a slow cooling is that any RA could stabilize. There is some issue with the newly created untempered martensite not being stable, but the RA is mostly it.
This is really more of a theoretical metallurgical discussion that a real world concern. As I regularly state, you will never be able to tell the difference. A laboratory might be able to tell....might! As far as blade quality and hardness, it won't matter if you cool it slow for an hour, wait overnight, or plunge it into ice water, between the tempers.
We are talking about single digit RA% in most carbon knife steels, and the cooling rate between tempers making a difference of a few hundredths of a % increase of that small percentage of RA. Without an x-ray diffraction or SEM in your shop, it would be hard for anyone to accurately detect.
As an example, lets assume that a blade had 10% RA ( which is probably much higher than it really would be if properly quenched). If a slow cooling rate between tempers increases that 10%, the final Ra would now be 11%. In actuality, it is more likely the difference would be 5% vs 5.05%. And even this small amount of RA would be reduced in the second temper.
On steels with high RA amounts, a third temper is useful, but there is a diminishing return after the second temper.