Differential harden vs diff temper

[rodriguez7]

So, I’ve been reading non stop about all this, and am in the process of testing some blades myself. Pics to follow eventually. What I’m wondering if clay coating is better than drawing the spine back with a torch, I don’t have enough time to test all these myself. I’m wanting to build 3 identical blades out of 15n20, clay coat 1, edge quench 1, and through harden 1 with a spine draw with a torch. I know with the edge quench, I loose some strength/easier to bend, but not break. But how does clay coating hold up? What kind of spine rc would I need for an extremely tough “survival knife”!!! Or am I over thinking this? I have broken a few blades in testing with a spine draw, I’m only reaching about a 45 degree bend with a torch draw on a blade with an rc of around 61-62. Guesstimate!! What are everyone’s thoughts on this? Has anyone done this kind of testing? I was able to bend a knife I did an edge quench on, 90 degree bends, back and forth, with about a 25 degree set on the blade after, but I haven’t tested a clay coated blade yet.

 

[Ian Fifelski]

I have never done any testing but I know that a clay quenched knife will have a more ductile spine than a spring temper spine. But in testing what would that mean? Maybe the ductile spine will bend farther but hold the bend more than a spring tempered spine that would spring back more. Interested in the tests, hope to see some pictures soon!

 

[Rick Marchand]

I have used several methods to harden blades..

Differential Hardening
Edge Quenching - Partial quenching. I stopped using it because I could not get past the uncontrolled variables... thermal mass, convection in the quench medium.
Torching - This one was much the same. The battle of thermal conduuctivity... how do you gauge temperature when the spine is relentlessly pulling heat from the edge?
Clay Coating - IMO, This is the most valid of the three. The only variable is the clay thickness and whether of not it stays adhered to the steel. The temperature can be controlled in a kiln and the quench medium is not hindered. The clay is the variable.

Differential Tempering
By far my favorite, when I think it is appropriate. There is some debate as to how much tempered martensite embrittlement comes into play but as far as I'm concerned, it is one of the most consistent methods of deferentially heat treating a blade.

Fully Hardened and Tempered
I always felt this was the way for slicing knives that wouldn't see much impact stress. After looking into TME (tempered martensite embrittlement) I feel that a decent full tempering is every bit as good if not marginally better than a differential temper.

I am still learning and may change my mind in light of new information... but for now, I'm right and you're wrong!

 

[rodriguez7]

So much to learn, thank you guys for weighing in. I guess the only way to know for sure is some crazy destructive testing. I was really happy when my edge quenched blade went back and forth on my bend test, I like a blade that doesn’t snap easily. Yet it was hard to bend. Guess I need to order some more steel, and keep trying. Hopefully more people comment on here.

 

[Willie71]

All of these techniques were developed at a time when steel sciences weren’t as developed as they are now. Folding steel, clay quenching, drawing back a spine all compensated for inconsistencies in the steel to prevent a crack from propagating through the blade resulting in full failure. We see this problem on FIF on many episodes. Smiths who make great blades use less than perfect equipment under extreme time constraint, and we see these failures.

With modern high quality steel, and proper heat treat, a fully hardened blade with a proper temper can withstand a lot of abuse. We can go in extremes such as S7 for toughness or hitachi White for a fine stable edge, but for the life of me, I can’t think of an application where I would need both in the same blade.

Maybe the bushcraft guys who fantasize about one knife they can use as a ladder, prybar, axe, and fillet knife, but I don’t go out in the Bush with only one knife expecting to do everything with it. I love a good hamon for the beauty of it, but I can get great toughness and pretty good edge holding with lowly 15n20. Step up to 3v or z-wear, and your expectations will be exceeded by a wide margin.

Are we looking for marketing claims, or real world performance increases?

 

[rodriguez7]

Well, my thoughts on this, is the people I build the blades for, mainly guides and outdoorsman. They all want just a single blade, they want something lightweight and really durable, that’s easy to touch up in the field. That’s why I’m using mainly 15n20. The feedback so far has been great. But this is me over thinking things, and wanting the most durable that I can possibly build, in such a thin lightweight knife! When I go out, I’m a blade nut, and usually take to many dam knives!!! I’m just trying to build something that won’t break regardless of what I’m doing to it! These guys are usually out for weeks at a time, in the middle of the gila wilderness here in New Mexico. Maybe fantasy, maybe possible reality! I’d rather not take a chance I guess, maybe I’m over exaggerating a bit. No clue!

 

[Willie71]

Well, my thoughts on this, is the people I build the blades for, mainly guides and outdoorsman. They all want just a single blade, they want something lightweight and really durable, that’s easy to touch up in the field. That’s why I’m using mainly 15n20. The feedback so far has been great. But this is me over thinking things, and wanting the most durable that I can possibly build, in such a thin lightweight knife! When I go out, I’m a blade nut, and usually take to many dam knives!!! I’m just trying to build something that won’t break regardless of what I’m doing to it! These guys are usually out for weeks at a time, in the middle of the gila wilderness here in New Mexico. Maybe fantasy, maybe possible reality! I’d rather not take a chance I guess, maybe I’m over exaggerating a bit. No clue!

I’m not meaning to be rude or harsh, so I hope it wasn’t taken that way. I use a lot of 15n20 for hunters who want easy to touch up. I run them at Rc62 for smaller knives. I might go rc60/61 for a chopper. I’ve not drawn back a spine in four years now. I’ve had zero knives returned with damage.

 

[rodriguez7]

I’m not meaning to be rude or harsh, so I hope it wasn’t taken that way. I use a lot of 15n20 for hunters who want easy to touch up. I run them at Rc62 for smaller knives. I might go rc60/61 for a chopper. I’ve not drawn back a spine in four years now. I’ve had zero knives returned with damage.

No sir, I understand where your coming from, you’ve helped me here with this steel, and I appreciate that. I just know how some of my customers use these things. Nothing has broke yet, and I’m hoping it stays that way. I guess it’s that differential heat treats really intrigue me! Whether it’s needed or not, I guess I enjoy trying different things! Thanks for your help!

 

[Lapedog]

How long and big are these knives rodriguez?

Is differential hardening even worth it with a blade that size and use? (I'm asking, i don't know) Even blades with differential hardening where the spine can bend and be bent back, the edge can still break. I have seen many pictures or videos of diff hardened where the spine is fine but the edge has a devastating crack.

Just wondering if like a spring temper or whatever might be better. (Again just throwing ideas)

 

[Willie71]

If you want indestructible, 15n20, 5160, 9260, 8670, and even 80crv2 at Rc58/59 would be nearly impossible to break. You will give up edge holding, but that’s the trade off you are looking for. I’ve not used S7 myself, so I haven’t listed it, but it’s extremely tough. Others can recommend hardness that works for super tough knives.

 

[JTknives]

If you want indestructible, 15n20, 5160, 9260, 8670, and even 80crv2 at Rc58/59 would be nearly impossible to break. You will give up edge holding, but that’s the trade off you are looking for. I’ve not used S7 myself, so I haven’t listed it, but it’s extremely tough. Others can recommend hardness that works for super tough knives.

After reading everything above I eco your post. Drop the hardness to just under 60 with 15n20 and you will have a very tough blade. It will be easy to sharpen and this might sound weird but it seams to hold true with at least how I sharpen. I find blades that are a tad lower on the RC I can get crazy scary sharp easier. If the steel is to hard to develop the wire edge that gets stroped off then the edge seams less keen. But you sacrifice edge holding but how much is any ones guess.

 

[jdm61]

OR you can go with though hardened that isn't TOTALLY hardened to the same degree in some places as in others. like with shallow hardening steels and a fairly thick spine. That is how you can get the "accidental hamon" on say W2 even even you use parks #50.

 

[jdm61]

JT, in your experience, how would 15N20 be as a "Western" sword steel assuming that you had a chunk big enough? Unfortunately, that would involve forge welding today, but we have seen some guys like Karl do that in the past. The normal steels for western swords seem to be 1065,1075, 9260, 5160, 6560,etc, but left rather soft in many cases. Obviously, hardness can look a bit different with the shallow hardening steels, but the stated numbers for factory "battle ready" western swords seem to be in the low to mid 50 range compared to the much higher edge hardness and lower spine hardness say in a Japanese style sword.

After reading everything above I eco your post. Drop the hardness to just under 60 with 15n20 and you will have a very tough blade. It will be easy to sharpen and this might sound weird but it seams to hold true with at least how I sharpen. I find blades that are a tad lower on the RC I can get crazy scary sharp easier. If the steel is to hard to develop the wire edge that gets stroped off then the edge seams less keen. But you sacrifice edge holding but how much is any ones guess.

 

[rodriguez7]

How long and big are these knives rodriguez?

Is differential hardening even worth it with a blade that size and use? (I'm asking, i don't know) Even blades with differential hardening where the spine can bend and be bent back, the edge can still break. I have seen many pictures or videos of diff hardened where the spine is fine but the edge has a devastating crack.

Just wondering if like a spring temper or whatever might be better. (Again just throwing ideas)

They vary in length, from 3 inches to about 7 inches. I ordered some steel, so some heavy testing is in order when I get some extra time!

 

[Lapedog]

OR you can go with though hardened that isn't TOTALLY hardened to the same degree in some places as in others. like with shallow hardening steels and a fairly thick spine. That is how you can get the "accidental hamon" on say W2 even even you use parks #50.

Strangely both my 440c La Griffe and my 12c27 Le Shark seem to have an auto hamon. The hamons are not put in on purpose on these production Perrins.