How to Heat Treat 5160 - Optimizing Toughness

Larrin Larrin , does quenching speed oil affects toughness, in your opinion? I mean, would a slower than Parks 50 cooling oil increase toughness? I ask this because the makers I know that use 5160 or spring steel equivalent (or near 5160 specs) don’t use parks50 oil and their knives (or swords) are tough to the point I’ve never heard one breaking (maybe I haven’t heard properly:D).
 
So tougher than the AEB-L but not quite as tough as the one nickel bearing steel that you have put though the ringer, 8670. I will be interested to see how the 80CrV2, 15N20 and L6 compare. Do you have any samples of the higher silicon steels like 9260 on hand?
 
jdm61 said:
So tougher than the AEB-L but not quite as tough as the one nickel bearing steel that you have put though the ringer, 8670. I will be interested to see how the 80CrV2, 15N20 and L6 compare. Do you have any samples of the higher silicon steels like 9260 on hand?
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You offered to send me some 9260 a while back.

80crv2, 15n20, L6 are all upcoming.
 
Would a grain refinement cycle help after the normalize? I’ve never used 5160 except for one stock removal hatchet years ago.
 
What I have heard for the years that I have been dong this is that 5160 can have some QC issues like other "commodity" steel like say 1095. I remember Ed Fowler and others saying that the 5160 that John Deere used for the accessory output shafts on their tractors was the best of the best. The problem was that you had to buy a $100 part to get the steel unless you knew how to get cutoffs. ;) I am sure that the stuff that guys like Ray Kirk have is quite good and I recall that Karl Anderson found a pile of some very high quality 1 inch square bar a number of years ago. Different stuff than the round edge 1/4 inch spring stock you get at your local steel supplier. I still have a couple of bars of 1 1/2 x 3/8 that I got from Uncle Al years ago.
 
To be clear I answered "maybe" to the previous two questions because it is difficult to predict the effect of any different heat treatment variable. And a different quenchant or an added cycle are not enough of a "universal good" to broadly recommend.
 
Larrin said:
To be clear I answered "maybe" to the previous two questions because it is difficult to predict the effect of any different heat treatment variable. And a different quenchant or an added cycle are not enough of a "universal good" to broadly recommend.
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I asked about the high speed quenching oil, because Fredrik Haakonsen once wrote: “Low alloyed steels can be quenched “softer” than unalloyed ones, giving an improvement in toughness.”. What does he mean with “quenched “softer””? Low speed quenching oil? If yes, it makes sense (at least, to me), the core of the piece takes more time to reduce temperature than the surface, making the hole piece tougher. If my idea is correct, then Marquenching would be even tougher, correct?
 
I don't know what softer quenching is. Regardless of quenching speed the core cools slower than the surface, the difference is more extreme with fast oil. Reported toughness with marquenching is a bit mixed and we haven't tried it, though there are some studies showing huge differences. It makes me think there were pre-existing quench cracks.
 
Marquenching is faster than oil quenching, it just lets it equalize before forming martensite.

Quench cracking is more of a problem with higher carbon steels and those with more alloy. More testing is needed for sure.

Hoss
 
Larrin said:
I don't know what softer quenching is. Regardless of quenching speed the core cools slower than the surface, the difference is more extreme with fast oil. Reported toughness with marquenching is a bit mixed and we haven't tried it, though there are some studies showing huge differences. It makes me think there were pre-existing quench cracks.
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Sorry, quench cracks in marquenched stuff? I thought that, if the difference between the austenizing temperature and the oil temperature was less, the probability of having quench cracks were far inferior!
 
DevinT said:
Marquenching is faster than oil quenching, it just lets it equalize before forming martensite.

Quench cracking is more of a problem with higher carbon steels and those with more alloy. More testing is needed for sure.

Hoss
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Thank you, Devin.

Some guys I know perform Marquenching in very hot insulated oil baths (160C/180C), and never had a problem. This is probably not Marquenching, because 180C is still below Ms transformation, but maybe a less stressful way to quench. One advantage for doing this is that is far easier to straighten the blade before it goes to room temperature. Haakonsen also marquenches his Vanadis 4 extra in 500C molten salt bath (http://kniver.blogspot.com/2007/08/herding-med-fredrik-jeg-har-ikke-lest.html?m=1) (sorry, it’s In Norwegian), or, at least, he used this process some years ago (now he has a new state of the art lab, he created his own company, and doesn’t share details about his heat treatment:().
 
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The chemical makeup of a steel determines 95% of it’s properties, provided that it is given a reasonable heat treat. The other 5% can be tweaked for optimum performance.

Carbide volume, type, size, and distribution have the greatest affect on wear resistance and toughness for knife steels. It would be impossible to make a steel with 20% carbide volume as tough as a steel with 5% carbide volume. It is also impossible to make a steel with 5% carbide volume as wear resistant as the steel with 20% carbide volume.

Optimum heat treating refers to getting the most out of a specific grade. There is always a sweet spot for every steel.

This testing does not represent the optimum heat treat for 5160, but does give someone a good starting point to figure out what that might be. There are some clear patterns shown here.

Hoss
 
hugofeynman said:
Thank you, Devin.

Some guys I know perform Marquenching in very hot insulated oil baths (160C/180C), and never had a problem. This is probably not Marquenching, because 180C is still below Ms transformation, but maybe a less stressful way to quench. One advantage for doing this is that is far easier to straighten the blade before it goes to room temperature. Haakonsen also marquenches his Vanadis 4 extra in 500C molten salt bath (http://kniver.blogspot.com/2007/08/herding-med-fredrik-jeg-har-ikke-lest.html?m=1) (sorry, it’s In Norwegian), or, at least, he used this process some years ago (now he has a new state of the art lab, he created his own company, and doesn’t share details about his heat treatment:().
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I have use low temp salt baht for marquenching for almost 2 years. Mostly I use it at around 400F for quenching steel like 52100 and O1.

I would say that marquenching does significantly reduce the chance of warpage and I believe marquenched blade also seems to be tougher.

But for higher alloyed steel like Elmax, XHP, M390 I found plate quenching yield higher hardness after subzero+tempering. Seems like marquenching does stabilized RA thus the freeze treatment would't be as effective.
 
hugofeynman said:
Sorry, quench cracks in marquenched stuff? I thought that, if the difference between the austenizing temperature and the oil temperature was less, the probability of having quench cracks were far inferior!
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The quench cracks would be in the poor toughness rapidly quenched steel.
 
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