Trying to better grasp the differential heat treat thing...

[PocketKnifeJimmy]

Specifically the method used by the Tops knife company, which is shown on a few videos online.
Craig at Tops describes their edge on their differentially heat treated 1095 steel to be in the 56-58 hardness range. He also states the spine to reach the 40'ish ranges. I am assuming that the middle maybe hits in the upper 40's to lower 50's ranges?... Am I correct that this is how it works? In other words, the edge at 56 to 58, and then progressively getting softer and softer as you go towards the spine, where it finally winds up being at that 40+ hardness range that Craig mentions?
I made this quick blade sketch to better explain my question, and to kind'a show what "I think" is found on such knives when this process is used.
Also, how low in hardness before the range is too low to hold any spring back feature? Does the middle and spine areas of the blade still retain some "springy-ness", or does it easily bend and stay bent?

Oh, and please don't criticise my sketch work... It just is what it is, lol!

 

[danbot]

Specifically the method used by the Tops knife company, which is shown on a few videos online.
Craig at Tops describes their edge on their differentially heat treated 1095 steel to be in the 56-58 hardness range. He also states the spine to reach the 40'ish ranges. I am assuming that the middle maybe hits in the upper 40's to lower 50's ranges?... Am I correct that this is how it works? In other words, the edge at 56 to 58, and then progressively getting softer and softer as you go towards the spine, where it finally winds up being at that 40+ hardness range that Craig mentions?
I made this quick blade sketch to better explain my question, and to kind'a show what "I think" is found on such knives when this process is used.
Also, how low in hardness before the range is too low to hold any spring back feature? Does the middle and spine areas of the blade still retain some "springy-ness", or does it bend and stay bent very easily?

Oh, and please don't criticise my sketch work... It just is what it is, lol!

I think you've pretty much got it.
Depending on how it's done, it could remain dead soft at the spine if you wanted. If you check out Ed Fowler's website, he has all kinds of info on differentially heat treated 52100 blades.
He etches them so that you can see the transition zones and bends them for destructive testing.

 

[PocketKnifeJimmy]

I think you've pretty much got it.
Depending on how it's done, it could remain dead soft at the spine if you wanted. If you check out Ed Fowler's website, he has all kinds of info on differentially heat treated 52100 blades.
He etches them so that you can see the transition zones and bends them for destructive testing.

I know that in one of the videos about Tops, Craig mentions their 1095 steel knife spine area reaches into the 40's range for hardness.

I don't know what the lowest hardness ratiing can be gauged at, but when you say that one could even get the spine to remain dead soft, I'm thinking that would likely have little benefit, correct? I mean, wouldn't the overall chance of too easily bending, and it staying bent, then exist? What would be the lowest hardness range that would still keep some spinginess, (if that's even a word), in the 1095 carbon steel? I mean springiness in the sense that it can get bent a certain distance, but still return to, or close to it's true.
Thanks in advance for any insight on this you may be able to share

 

[danbot]

If you were to use the knife as a crowbar, then sure, it would be easier to permanently bend a knife with a dead soft spine. But even a short piece (say, 5 inches long) of soft 1095 at 1/4" thick will take much more force to permanently bend than you should ever put on a knife.

That being said, I believe a typical hardness range for a spring temper in 1095 is generally 40-50 HRC. And the thinner the blade, the higher the hardness should be (within that 40-50 HRC range).

Hope this helps!

 

[davek14]

Don't know how much this is helps but this guy does some backyard differential heat treat. Years ago when files were usually good quality, not case hardened, I worked in a big plant which threw away dull knife files. I used to grind on the spine with a worn out belt sander belt and try to get it to turn blue, but not have the blue reach the edge. Yes, if I overdid it they wouldn't be springy enough. 62 rockwell made a great cutting edge though. Made easy knives for trading at pow wows and re-inactments.

http://www.primitiveways.com/pt-knives-1.html

http://www.primitiveways.com/Steel heat treatment.html

 

[PocketKnifeJimmy]

If you were to use the knife as a crowbar, then sure, it would be easier to permanently bend a knife with a dead soft spine. But even a short piece (say, 5 inches long) of soft 1095 at 1/4" thick will take much more force to permanently bend than you should ever put on a knife.

That being said, I believe a typical hardness range for a spring temper in 1095 is generally 40-50 HRC. And the thinner the blade, the higher the hardness should be (within that 40-50 HRC range).

Hope this helps!

That is very helpful, thank you.
You saying that the 40 to 50 hardness range is likely the "spring temper" zone for 1095... Now it makes more sense to me that Tops would state the 40'ish range on the spines of their differentially heat treated 1095 carbon steel blades. The 56 to 58 hardness for their edge to retain decent sharpness, then progressively getting softer as one goes towards the spine, (but still being hardened enough to remain in a "spring temper" zone for added blade toughness).
Again, numbers like that are what I was looking for, thank you!