With modern steel, is a differential quench ever superior?

kuraki

kuraki

Fimbulvetr Knifeworks
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As I'm standing in front of the furnace with some w2 and 80crv2 blades being thermal cycled I'm wondering about this. I'll be trying to produce hamon with the w2 for appearance sake, but is there really a reason for performance?

I understand the idea of a hard edge and relatively soft spine. I understand why techniques like this were developed, given the methods and materials available, east or west.

My problem with the supposed advantage with modern steel is my perception that a transition in hardness also creates a fault line. Maybe not a significant one, but more than would exist in a through hardened blade or tool.

I could however be wrong and I'm sure this has been discussed before, so my question focused: will a differentially hardened w2 blade with the same edge hardness, grain refinement, etc annually be superior to a through hardened w2 blade of the same physical characteristics? And if so, in what way?

I'm not trying to stir anything up, I'm going to keep trying to achieve hamon like some of the masterful work posted here, but I doubt I'll be tempering any spines with a torch or edge quenching again, unless at a customer request.
 
Hamons are cool, but today's steels don't benefit from that kind of heat treat, as far as I can tell.
 
Technically speaking I don't really think any steel benefits, it is better to convert fully then draw the spine back if that is needed.
 
Daniel, doing it that way must achieve a "softer" transition, but does the added toughness in the spine actually help support the harder edge? Or if it is abused by say lateral bending, will the edge break perpendicular to the spine, while the spine springs back?
 
kuraki said:
Daniel, doing it that way must achieve a "softer" transition, but does the added toughness in the spine actually help support the harder edge? Or if it is abused by say lateral bending, will the edge break perpendicular to the spine, while the spine springs back?
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I think under extreme stresses, both sections will act independently of each other. Not sure if the method they used to produce this katana and euro longsword were accurate but I think this video shows clearly what happens.

https://www.youtube.com/watch?v=w_3W1zg683A

Skip to 5:40.
 
Oh thanks for the video link, for a number of reasons.

I was wondering more about how a knife might be used to pry, though I believe the results would be similar.
 
A fully martensitic blade with good grain structure is the best. I don't even know if drawing back the spine has real benefit with a good heat treat. Compensating for a bad heat treat or inconsistent steel is where differential hardening or tempering has benefits. It compensates for other problems.
 
I love a hamon, but Willie is right - martensite is better than pearlite in a knife blade. If you have a use that requires a softer spine, draw back the temper on the spine.

Generally speaking the perfect blade is:
100% fine grain martensite
evenly and properly tempered at the correct hardness for the task
 
Katana is a weapon .In fight soft spine is good for blocking impact of the opposing katana..........
 
Natlek said:
Katana is a weapon .In fight soft spine is good for blocking impact of the opposing katana..........
Click to expand...

You should watch the video.

San mai is a different animal. Composite materials can often exceed the performance of the sum of their parts.
 
Well , I watched the video .They use German sword to brake another one German sword ? And If they use that German sword on katana I don t think that katana will brake like this German sword do ? What is better broken sword or bend katana ? Broken knive or bend knive ?
 
Katana blade is designed to cut an opponent .The opponent with a katana block strike with spine of catana/which is soft/ not with edge . And that mind that katana will have little damage to the edge .....
 
If the test was repeated on a katana the results would have been same or similar. The answer to your question is neither. The fully hardened sword in motion will have the advantage over a fully hardened or differentially hardened sword in stasis.
 
kuraki said:
If the test was repeated on a katana the results would have been same or similar. The answer to your question is neither. The fully hardened sword in motion will have the advantage over a fully hardened or differentially hardened sword in stasis.
Click to expand...

I do not think so. Soft spine will absorb the shock of full hardened sword .But you're right ......fully hardened sword in motion will have the advantage over a fully hardened or differentially hardened sword in stasis
 
Katana is the most commonly used against katana, means the same manufacturing technology. The Japanese are not that crazy to make swords which will break on first strike ? Both have soft spine , both are blocking strike with spine , where things can go wrong ?
 
That's not what the thread is about. I wanted to know if there was consensus on which technology was superior.
 
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