52100 quench time and oil temp?

M

MM52100

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Dec 29, 2020
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Hey guys, simple questions. How long do you dunk 52100 and do you pre-heat your oil?

Do you quench until the metal is close to oil temp or a determined time that you know gets you below a temp but still hot? I did a HT tonight and got a small warp, I think it could be avoid by using better technique. I dunked for 20 seconds and the oil was room temp.

I'm using a medium speed oil, which I think most people use. In my case McMaster 11sec.

Thanks!
 
Most quench oils are heated to 120-130°F before the quench. Parks #50 is the exception and is used at room temperature 70-80°F.
You only need to quench the blade long enough for it to drop below the pearlite nose, which is at 1000°F. This happens in less than a second. Most folks quench and count to eight, pull the blade out and straighten any warpage, and then stick the blade back in for another 30 seconds to allow it to cool slowly down to 400°F, which is when the conversion to hard martensite starts. After the initial quench and before it gets to 400 it is a soft austenite structure and can easily be straightened. You have at least 10-15 seconds to do any straightening. If the blade starts to feel stiff. STOP straightening and wait until after tempering to do any further straightening. Post tempering straightening is done at 400°F. Some folks straighten during the temper with clamps and such.
 
MM52100 said:
Hey guys, simple questions. How long do you dunk 52100 and do you pre-heat your oil?

Do you quench until the metal is close to oil temp or a determined time that you know gets you below a temp but still hot? I did a HT tonight and got a small warp, I think it could be avoid by using better technique. I dunked for 20 seconds and the oil was room temp.

I'm using a medium speed oil, which I think most people use. In my case McMaster 11sec.

Thanks!
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Books I read says that steel should be put in tempering oven on about 60 Celsius /140 F , not to let cool down to room temperature ........
 
Natlek said:
Books I read says that steel should be put in tempering oven on about 60 Celsius /140 F , not to let cool down to room temperature ........
Click to expand...
It looks as though 52100 finishes martensite conversion above 200F. I wonder if there are RA(retained austenite) issues that allowing it to cool further would mitigate?
 
Those books are probably based on industrial bearing, large item manufacture, and similar industrial use.
Knives are different than bearings and railroad car chassis.
Most carbon steel starts hardening (Ms) at 400F and finishes (Mf) around 200F. Some alloys drop to nearly room temp before Mf, but those are higher alloy steels. In the mass of a knife, these things happen in a short periods of time.

I'll have to looks at Larrin's charts when I get home, but I can't see a reason not to let a 52100 knife reach room temp before tempering. RA stabilization is a factor of time and temperature. A blade cooled to room temp and then tempered promptly would have no additional RA beyond any other parameters. Also, in a knives, RA isn't as big a deal as it is in the aerospace industry.


All knife tempering should be done ASAP after the quench and cooling to room temp.
 
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Stacy E. Apelt - Bladesmith said:
Most quench oils are heated to 120-130°F before the quench. Parks #50 is the exception and is used at room temperature 70-80°F.
You only need to quench the blade long enough for it to drop below the pearlite nose, which is at 1000°F. This happens in less than a second. Most folks quench and count to eight, pull the blade out and straighten any warpage, and then stick the blade back in for another 30 seconds to allow it to cool slowly down to 400°F, which is when the conversion to hard martensite starts. After the initial quench and before it gets to 400 it is a soft austenite structure and can easily be straightened. You have at least 10-15 seconds to do any straightening. If the blade starts to feel stiff. STOP straightening and wait until after tempering to do any further straightening. Post tempering straightening is done at 400°F. Some folks straighten during the temper with clamps and such.
Click to expand...
I’m not entirely sure what happened, but late last year I tried to straighten a warped blade during temper by clamping it to another piece of steel. After the second cycle, I loosened one of the clamps and at some point, the blade snapped in half during one of the temper cycles.
 
Here is some data on L3 steel that is relevant to this discussion:
interrupted-quenching2.jpg
 
Thanks everyone, this helps a ton. At the least, I need to put a little heat into the oil. I imagine my oil was in the mid-low 50's, overnight garage temp.

Larrin, thanks for the table, very helpful. Do you have a recommended max RA in 52100 for those not planning on doing cryo treatment? Maybe a better question, is your data on 52100 based on a 68f quench?
 
TheEdge01 said:
I’m not entirely sure what happened, but late last year I tried to straighten a warped blade during temper by clamping it to another piece of steel. After the second cycle, I loosened one of the clamps and at some point, the blade snapped in half during one of the temper cycles.
Click to expand...

Any straightening attempt should start at 400F don't clap while cold. If straightening during the temper cycle, let blade come up to 400F and then clamp to the straightening bar before returning to the tempering oven.

MM52100 - The 68F is room temp. The quench is at the normal temperature of the quenchant tested. In Larrin's chart the water or oil quenchants would be 120F. The salt pot was 450F in order for the test metal to be fully austenite when removed. What he was showing is that if the blade is still fully austenite and is slow cooled in air, the RA is highest. If it is fully austenite and fast cooled in water it cuts the austenite almost in half.

When doing the method I was posting, once past the pearlite nose (and quickly checked), the blade stays in the oil as it cools down to 400F. It is super-cooled austenite during the cooling from 1000F to 400F. After passing 400F it starts to convert to martensite. Once at room temp (68F) the conversion has finished. The RA should be the same as Larrin's "oil quenched to 120F (the temperature of the oil) and air cooled to 68F". The only way to push the RA any lower would be to use a violent water quench ( not a good idea), or to have a salt pot and follow that with a fast water cooling (expensive equipment).
My other point is that while metallurgists test and have concern of 7%RA vs 9%RA, knifemakers shouldn't loose any sleep over it. The blade will be fine either way.


BTW, 52100 does need cryo like other steels do.
 
TheEdge01 said:
I’m not entirely sure what happened, but late last year I tried to straighten a warped blade during temper by clamping it to another piece of steel. After the second cycle, I loosened one of the clamps and at some point, the blade snapped in half during one of the temper cycles.
Click to expand...
Any straightening should be done AFTER first temper .....you know that , right ?
 
Natlek said:
Any straightening should be done AFTER first temper .....you know that , right ?
Click to expand...
I always try to straighten before the blade cools after quenching, but that one didn’t work out. I didn’t think clamping it would put too much stress on the blade but obviously I thought wrong.
 
Stacy - That's a great point on the straightening temp. I was planning on attempting that and would have done it cold.

I should have been more clear with my question to Larrin. What I meant was in the data in his book there are toughness and hardness charts based on different austenitizing and tempering procedures and I was wondering if those were done with a constant quench procedure. That would inform my decision on how to adjust my routine. The above chart has an RA for 68f oil and 120f oil plus air cooled to 68f but based on what you said it doesn't matter and I shouldn't lose sleep over it. That works for me.

I'm starting to wrap my head around the science, when I have more empirical experience of a standard quench I will give a marquench/martemper a try. That said, it is fascinating that you can temporarily stall the martensite transition and end up with equal results, sneaking in under the pearlite transition. Does that process also result in some retained bainite or will that turn into martensite?

I do really appreciate the help. This is a fantastic community.
 
TheEdge01 said:
I always try to straighten before the blade cools after quenching, but that one didn’t work out. I didn’t think clamping it would put too much stress on the blade but obviously I thought wrong.
Click to expand...
That is OK to try , but if not work any future straightening should be done AFTER first tempering cycle was done .You don t try to straighten blade on first temper ..... Just to be clear what I m trying to say ....
 
Natlek said:
That is OK to try , but if not work any future straightening should be done AFTER first tempering cycle was done .You don t try to straighten blade on first temper ..... Just to be clear what I m trying to say ....
Click to expand...
Thank you sir
 
Glad to help.

Natlek has a good point. I mentioned it in an earlier post, but to elaborate:
When you do the first temper, the blade is brittle martensite. After tempering it is tempered martensite. If you attempted to straighten the blade by clamping it to a bar and sticking in the oven on the first temper it could easily snap in half. Once up to 400F it is more stable, but it is always best to do the straightening on the second temper. If it still needs more straightening, you can do more cycles as needed. The blade will not soften appreciably.
Remember - a straight blade at Rc59 will make a much better knife than a warped blade at Rc60.

Extra credit nerd stuff;
The second temper is mainly to temper any new brittle martensite that came from RA which was converted to brittle martensite in the first temper. In steels with little or no RA, a second temper probably is redundant, but it is always a good idea.

In steels with high alloying, and thus higher RA after hardening, sometimes a third temper is required.
 
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