High vs Low Tempering?

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shqxk

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Mar 26, 2012
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We all know that low range tempering plus freezing as part of the quench will yield higher toughness and corrosion resistance. But doesn't high tempering will lead to better yield stress due to even lower RA and should be higher wear resistance too due to more carbide in the matrix?

For steel with high amount of Mo for secondary hardening effect 4V do you think high tempering should be a better choice for fine edge performance? if toughness and rusting is not a concern.
 
I'm not a metallurgist and I don't fully understand the science behind heat treatment, but what I have learned from more experienced people is that: lower temper with cryo will increase wear resistance and corrosion resistance with little sacrifice in toughness.

The reason datasheet from Crucible, Bohler recommend using high temper is because their main focus is making industrial dies, using higher temper will eliminate RA, increase toughness and stability but will sacrifice wear resistance and corrosion resistance.

If you look up threads reagarding heat treating 3V, CruWear in the mid 2000s, many makers were using the high temper as the manufacturer recommend, but later, in the mid 2010s, people started discovering that lower temper with cryo boost wear resistance and corrosion resistance. Delta 3V is a prime example of superior performance.
 
For fine edges, low temper is a measurable improvement in every steel tested except M2, and both were equal in that steel. Cracks start along carbides, and the secondary carbides produced during high temper increase the number of potential places to start cracking. Interestingly, the secondary carbides did not cause an increase in edge holding in Larrin’s tests. CRYO, producing ETA carbides didn’t result in measurable improvement either.

high temper works fine for industry, and minimizes warp and distortion risk. They use much more complicated shapes than we do.
 
shqxk said:
We all know that low range tempering plus freezing as part of the quench will yield higher toughness and corrosion resistance. But doesn't high tempering will lead to better yield stress due to even lower RA and should be higher wear resistance too due to more carbide in the matrix?

For steel with high amount of Mo for secondary hardening effect 4V do you think high tempering should be a better choice for fine edge performance? if toughness and rusting is not a concern.
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For 4v? Nah, austenitizing temperature is more important.

I noticed you ran your MagnaCut with a higher temper.
 
DeadboxHero said:
For 4v? Nah, austenitizing temperature is more important.

I noticed you ran your MagnaCut with a higher temper.
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Up to now, I have ran 3 batches of Magnacut, the first two is 2070F, dry ice subzero and 350F tempering. The last one is 2160F and 960F tempering. Both came out at around 62HRC. I and my knifemaker friend did some robes cutting tests and found the later protocol to hold an edge slightly better. But for stainless I think maximizing corrosion resistance would be a more suitable route anyway. 4V is just for an example since it has even higher secondary hardening response and the corrosion resistance won't be a big concern.
 
shqxk said:
Up to now, I have ran 3 batches of Magnacut, the first two is 2070F, dry ice subzero and 350F tempering. The last one is 2160F and 960F tempering. Both came out at around 62HRC. I and my knifemaker friend did some robes cutting tests and found the later protocol to hold an edge slightly better. But for stainless I think maximizing corrosion resistance would be a more suitable route anyway. 4V is just for an example since it has even higher secondary hardening response and the corrosion resistance won't be a big concern.
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"Hold an Edge slightly longer" maybe it's within the scatter of the testing.
 
I wonder if a high tempering temperature would be a better option for post tempering heat related activities like machine sharpening and DLC coating?
 
Lorien said:
I wonder if a high tempering temperature would be a better option for post tempering heat related activities like machine sharpening and DLC coating?
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This is part of the reason industry recommends high temper.
 
just looked into DLC and it's applied at 300F, so I was talking out of my ass
 
Lorien said:
I wonder if a high tempering temperature would be a better option for post tempering heat related activities like machine sharpening and DLC coating?
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Some type of PVD is operated at over 900F so high-temperature tempering is a must.
 
Not to be controversial, but I tested low vs high tempering with 4V for edge retention (I'm not talking about plain abrasive wear resistance) and there was a significant difference in controlled testing. We're using that alloy on our competition cutters (which we use to win almost every competition we attend) and the high temp chips, rolls and behaves mushy showing edge damage that would get a competitor points deduction, where low temp 4V shows very little edge deterioration in our cut tests. 4V is a very good candidate for the low temp tweaks, the improved edge retention from superior edge stability is unambiguous. And, although we did develop our own heat treat for it, we found that Peters had developed a similar HT and it is available to everyone and works very well.
 
Nathan the Machinist said:
Not to be controversial, but I tested low vs high tempering with 4V for edge retention (I'm not talking about plain abrasive wear resistance) and there was a significant difference in controlled testing. We're using that alloy on our competition cutters (which we use to win almost every competition we attend) and the high temp chips, rolls and behaves mushy showing edge damage that would get a competitor points deduction, where low temp 4V shows very little edge deterioration in our cut tests. 4V is a very good candidate for the low temp tweaks, the improved edge retention from superior edge stability is unambiguous. And, although we did develop our own heat treat for it, we found that Peters had developed a similar HT and it is available to everyone and works very well.
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It sounds like you are not controversial at all. All real world and lab testing is agreeing with you.
 
"but I tested low vs high tempering with 4V for edge retention (I'm not talking about plain abrasive wear resistance)" Thank you Nathan. There is a distinction between "edge retention" and "wear resistance" that, for whatever reason, is not making sense to some in this community. As far as I understand, the high temper treatments are actually slightly more wear resistant than the low temper treatments. But on the flip side, the low temper treatments are tougher (can stand impact better), which gives a better "edge retention" because of "chips, rolls, and mushy showing edge damage". And the reason for this is because the high temper treatments rob carbon to form tempering carbides (better wear resistance), but the matrix surrounding the carbides is robbed of the carbon that make it strong, supporting the carbides (primary and tempering).

So while the high temper protocols might be slightly better at, say, rope cutting because of slightly better "wear/abrasive resistance", this does not at all mean that the high temper protocol gives better "edge retention".
 
samuraistuart said:
"but I tested low vs high tempering with 4V for edge retention (I'm not talking about plain abrasive wear resistance)" Thank you Nathan. There is a distinction between "edge retention" and "wear resistance" that, for whatever reason, is not making sense to some in this community. As far as I understand, the high temper treatments are actually slightly more wear resistant than the low temper treatments. But on the flip side, the low temper treatments are tougher (can stand impact better), which gives a better "edge retention" because of "chips, rolls, and mushy showing edge damage". And the reason for this is because the high temper treatments rob carbon to form tempering carbides (better wear resistance), but the matrix surrounding the carbides is robbed of the carbon that make it strong, supporting the carbides (primary and tempering).

So while the high temper protocols might be slightly better at, say, rope cutting because of slightly better "wear/abrasive resistance", this does not at all mean that the high temper protocol gives better "edge retention".
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I think it's possible that precipitating additional carbide could give higher wear resistance in certain kinds of applications, but it seems to me that all else being equal, a hard, strong, carbon saturated martensitic matrix supporting that carbide is going to be better than a soft over tempered matrix. Or, put another way, if you want tons of carbide just select a steel with more carbide. But any optimal solution would have the matrix at its strongest most robust potential.

We are unencumbered by high temperature requirements like cutting tools and the dimensional stability constraints and need to minimize risk of distortion and cracking like tool and die.
 
Nathan the Machinist said:
Not to be controversial, but I tested low vs high tempering with 4V for edge retention (I'm not talking about plain abrasive wear resistance) and there was a significant difference in controlled testing. We're using that alloy on our competition cutters (which we use to win almost every competition we attend) and the high temp chips, rolls and behaves mushy showing edge damage that would get a competitor points deduction, where low temp 4V shows very little edge deterioration in our cut tests. 4V is a very good candidate for the low temp tweaks, the improved edge retention from superior edge stability is unambiguous. And, although we did develop our own heat treat for it, we found that Peters had developed a similar HT and it is available to everyone and works very well.
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By any chance did you ever have any experience with M4? I'm making a large knife right now and was just going to run with high temper since the seal on my dewer broke and it doesn't hold. If it makes a big difference I can profile a sheet of M4 that I have been sitting on for a few years so it's worth the expense of having the dewer filled for a single HT. I finally moved into a place where I have power for my oven again.
 
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