Waiting between quenching and tempering

A

A-V

Member
Hello,

So here are two questions :

#1 - You heat treat then quench a blade, you don't have time to do the tempering (or second tempering) today so you wait till the next day to do it. Does the steel suffer from this?

#2 - You do one temper, take the blade out and it quickly cools to room temperature. Do you wait before putting it back in or you can basically dip it in water to cool it and put it back immediately for the second temper?

Also, I don't do any cryogenic treatments as my budget doesn't allow it.

Thank you for your time !
 
#1 It may crack. Put it in your kitchen oven at 200 degrees or so for awhile.

#2 Wait until it's at room temp., then temper again.
 
Waiting to temper isn't advised, but sometimes it's unavoidable. Quenching after temper is even recommended in some circles.
 
you should try to temper at least once as soon as quenched. for high carbon steels, at least half an hour at 300F. if really in a hurry, heat oven to 350F, put the blade in, once oven is back to 350F, turn it off with the blade inside.
 
I think you have more latitude with the stainless steels than with carbon steels. My HT oven takes forever to cool down to drawing temp. Because of this, I have often left 440C and S35VN blades to be tempered the next day and I've never had a problem. I just recently started into using W2 and ended up purchasing a Kitchenaid countertop oven because I'm confident I will not be able to let those blades sit around untempered for any length of time.

Bob
 
As I understand, the BIG reason an immediate temper is desired is to prevent possible crack in blade. Right out of quench most steels are so "brittle" they will crack just by looking at them...... sometimes don't even require you to look at them for blade to crack. You'll just hear that dreaded "ping". A quick snap temper at 200 to 300ºF will (should) prevent this horrible sound.

I think your original question was "IF" you do leave blade un-tempered for a day or so after quench does it damage the blade. Provided it doesn't crack - I'm not sure there is any damage to blade, unless the internal stresses could build to the point of weakening the blade, but not cracking. I'd be interested in comments on that.

Ken H>
 
One thing to remember about tempering "immediately" is that you must allow the steel to cool to ambient temperature to make sure that it has gotten past the M[sub]f[/sub] point. Getting the blade into a tempering oven too soon can prevent the steel from reaching full hardness. There are some who have found that allowing steels like 1095 to cool for around an hour at ambient temperature allows it to reach full hardness. Regardless I wouldn't put a blade into a tempering oven that hasn't cooled enough to handle with bare hands.

Doug
 
"I wouldn't put a blade into a tempering oven that hasn't cooled enough to handle with bare hands." -Amen! Ditto! I wonder how many blades are quenched AT non magnetic!? And how many blades go into the tempering oven while martensite is still being formed!?!?
 
Seriously, the drastic change in temperature due to the quench causes so much stress inside that the steel may crack across the weakest point. This may not show up until the knife is used. :s12202::cursing:
 
A-V said:
I'm certainly not a metallurgy expert so could you please explain me what is wrong with quenching at non magnetic? Should you wait before quenching that steel becomes magnetic again ?
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Uh-huh....my point exactly right here. A-V has probably read somewhere online (probably a few different places), where someone says to quench AT non-magnetic. Non-magnetic is right around 1414F. If you are using 1084 steel, you need to be quenching at 1500F. And if you are using a hypereutectoid steel, the current wisdom says to quench at 1475F, or put more carbon in solution and deal with the RA.

Point being....non-magnetic is not hot enough. You still need another 85 degrees F to go!!!!!! Now I'm really glad I mentioned it.
 
At just non-magnetic, 1414°, is not hot enough to allow the steel to fully form a good homogenous solution of the iron, carbon, and other alloys, if present. With the more common carbon steels, that requires a heat range between 1450° and 1500°, with 1475° being ideal for most, and about maximum for most that have more than .77% carbon. Allowing at least a short soak at that temp is beneficial, then it is quenched. You do not allow the blade to cool before quenching. That would defeat the purpose of quenching. Once at non-magnetic, magnetic attraction will not return until the steel cools to somewhere below 900/1000°. In the tempering process, quenching in water between tempers helps to convert any retained austenite into more martensite, allows the next temper to be started immediately, and at worst, does absolutely no harm. Not sure, but last I saw, 1084, being right on the division, may be better treated as a hypereutectic. Probably no harm either way, but 1500° may cause unnecessary grain growth. Surely not a harmful amount, but still unnecessary.
 
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LRB said:
At just non-magnetic, 1414°, is not hot enough to allow the steel to fully form a good homogenous solution of the iron, carbon, and other alloys, if present. With the more common carbon steels, that requires a heat range between 1450° and 1500°, with 1475° being ideal for most, and about maximum for most that have more than .77% carbon. Allowing at least a short soak at that temp is beneficial, then it is quenched. You do not allow the blade to cool before quenching. That would defeat the purpose of quenching. Once at non-magnetic, magnetic attraction will not return until the steel cools to somewhere below 900/1000°. In the tempering process, quenching in water between tempers helps to convert any retained austenite into more martensite, allows the next temper to be started immediately, and at worst, does absolutely no harm. Not sure, but last I saw, 1084, being right on the division, may be better treated as a hypereutectic. Probably no harm either way, but 1500° may cause unnecessary grain growth. Surely not a harmful amount, but still unnecessary.
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Nice! Great thoughts!!!
 
I quench my Damascus, 1095/15n20 at approx 1450. I have a turkey oven, I purchased at a box store for around $30. Before I start my quench I turn on the oven with canola oil at 340-350, after quench I let the blades soak 3-4 hrs in the oil. Turn off the oven and let the blades cool. Clean up with kitty litter and a degreaser. Dlee
 
Seems to me that you are slowing/retarding MF. What is the advantage of having the oil that hot, and then soaking for hours?
 
"If you don't temper immediately after quenching the steel might crack..." Is this really true, or another of the many knife-making myths?

I always cryo my blades by soaking them in liquid nitrogen for 12 - 24 hours after quenching (depending on type of steel), and only then do the first temper - most times I will do 2 tempers, each time quenching from the 180°C - 240°C tempering temperature (again depending on type of steel and required hardness...) directly into water, and I have only had one blade crack due to a too rapid heating after removing from the nitrogen. I believe that most people who cryo do so without first tempering the blades (this will reduce RA the most, as a temper before cryo will "set" some RA and prevent it from converting back to martensite).

So, why do blades crack if left over night at room temperature, yet do not crack if kept the same time at the *much* colder temperature of liquid nitrogen?
 
It is true. But predicting it is an effort in futility. I've had one blade crack in my life. A W2 brine quench. It survived the quench (it should), but it did not survive martensite formation. 400f-100f. In that temp range, for carbon steels anyway, martensite formation starts at around 400f or so. The formation of that martensite is what induces strain on a knife. Sometimes it can be so severe, it will crack on it's own. Like mine did. Just laying on the counter a few minutes after the quench.......I had two pieces. But another knife identical.....survived.

Strain energy induced by martensite formation is hard to pin down exactly what it is going to do to a blade. Say your prayers!
 
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