how hard should a thin blade be?

B

bill may

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Jul 30, 2014
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Alright I've have taken a 2 inch piece of 1084 3/16 thick and 1 inch wide that's just my blade specs handle not included. I have drawn that 2 inch to 3 inch's and the 3/16 down to a 1/16 at the tip. I have hardened and tempered it to 55 Rockwell. My question is have I made it to hard is it going to leave that thin tip brittle? I have thought about putting the edge in water and using a torch on the spin or should I put it back in the oven and try to bring hardness down some or am I just over thinking it? interested to see what you guy's think
 
55HRC is already too soft, IMO. There is really no need to temper back the spine of a knife meant for general use... especially one as short as yours. If you achieve full hardness in the quench, tempering 1084 between 400F-450F will give you a nice range to work with for edge retention vs. toughness.
 
We usually run our smaller thinner knives 61-62. Some 63-64.

Larger knives and choppers 60+

I made Dan's knife here at 63.5 and it's only .020 behind the edge and it's pretty durable.


I think good steel with a good heat treat shouldn't need to be so soft. That hedge against breaking really isn't necessary today.
 
Nathan the Machinist said:
We usually run our smaller thinner knives 61-62. Some 63-64.

Larger knives and choppers 60+

I made Dan's knife here at 63.5 and it's only .020 behind the edge and it's pretty durable.


I think good steel with a good heat treat shouldn't need to be so soft. That hedge against breaking really isn't necessary today.
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I didn't realize you made knives in 1084. That seems pretty hard but maybe you know something I don't.
 
Nathan the Machinist said:
We usually run our smaller thinner knives 61-62. Some 63-64.

Larger knives and choppers 60+

I made Dan's knife here at 63.5 and it's only .020 behind the edge and it's pretty durable.


I think good steel with a good heat treat shouldn't need to be so soft. That hedge against breaking really isn't necessary today.
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Nice! Anyone know if he will appear on the Knife or Death show?
 
Thank you guy's for the useful information sounds like I'm going to have to modify my tempering process so I retain my hardness. but now I know were to take it to. thanks again
 
Nathan the Machinist said:
We usually run our smaller thinner knives 61-62. Some 63-64.

Larger knives and choppers 60+

I made Dan's knife here at 63.5 and it's only .020 behind the edge and it's pretty durable.


I think good steel with a good heat treat shouldn't need to be so soft. That hedge against breaking really isn't necessary today.
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Very impressive I've never seen competitons like that before good job.
 
bill may said:
Thank you guy's for the useful information sounds like I'm going to have to modify my tempering process so I retain my hardness. but now I know were to take it to. thanks again
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I don't think Nathan is talking about 1084. He tends to use 3V, I think... which is very different.
 
Rick Marchand said:
I didn't realize you made knives in 1084.
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I have made a few in 1084...

The question was "how hard should a thin blade be?" In my opinion the answer is 55 is way too soft and I like the low 60's. We're not producing patterns in 1084, but Elmax, AEBL, D2, A2, 3V, 4V and V4E are all run in the mid to low 60's and I think 1084 would do okay there too. Won't it?

I see running blades soft as hedge for poor steel quality or poor heat treat so it doesn't break. The reality is a soft thin knife is easy to damage, it takes some strength to support thin geometry.


Rick Marchand said:
maybe you know something I don't.
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oh my god yes...

:D
 
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Just to clarify, I never make knives below Rc60. I suggested Rc58 and higher because people heat treating in a forge with canola oil might choose to go a bit softer because of inconsistent structures.

I’ve used 1084 at Rc61-62 in small knives, and they hold up fine.
 
My standard starting point for anything made with 1084 is 1500/400 which, according to Mr. Cashen and others, should give you hardness in the 61 Rc range. I temper a bit cooler for damascus kitchen knife blades of 1084/15N20.
 
Nathan the Machinist said:
I have made a few in 1084...

The question was "how hard should a thin blade be?" In my opinion the answer is 55 is way too soft and I like the low 60's. We're not producing patterns in 1084, but Elmax, AEBL, D2, A2, 3V, 4V and V4E are all run in the mid to low 60's and I think 1084 would do okay there too. Won't it?

I see running blades soft as hedge for poor steel quality or poor heat treat so it doesn't break. The reality is a soft thin knife is easy to damage, it takes some strength to support thin geometry.




oh my god yes...

:D
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The OP was asking SPECIFICALLY about the 1084 blade he had made and you suggested 61-62, which I agree with for 1084... but then went on to say 63-64RC and showed a video of a knife at 63.5 RC. I just thought that was a bit misleading... maybe he understood you were talking about high alloy steel but other folks might not
 
In reply to the OP - 1084 thin blades do fine at Rc 60-61. I have made dozens that were .060" to .090" thickness and never had a problem.
 
As a general rule, being thin doesn't mean that you need to temper to a lower hardness. A thin blade at a given hardness in a given alloy will have a tighter minimum bend radius and be less prone to break with a given amount of bend (than would a thicker blade). You can see this with edge rolling. A thin geometry edge is more prone to edge rolling than chipping, when compared to a thicker geometry. Put another way minimum bend radius gets tighter as steel gets thinner at any given hardness.

Now all of this ignores the fact that a thicker blade is stronger, due to the additional material, allowing it to withstand more abuse in some circumstances. But there is no rule that thin blades should be softer than thick blades.

I generally think that you should consider the variables in the reverse. Which is to say, determine a blade thickness based on use and desired geometry, then get it as hard as you can without experiencing major negatives. For something like a kitchen knife, that would be generally a very thin blade at high hardness. For a general use folder, it would be similar (though maybe a bit thicker and a point or two softer). For a heavy chopper, something thicker to give mass and rigidity with a lower hardness and comparatively higher toughness.
 
Wow I haven't checked this thread in a few days. My general question was would over hardening a thin blade make it brittle and I got a lot of good answers thank you very much out here on my own trying to piece this stuff together it helps. I appreciate you guy's taking the time to help me out.
 
bill may said:
Wow I haven't checked this thread in a few days. My general question was would over hardening a thin blade make it brittle and I got a lot of good answers thank you very much out here on my own trying to piece this stuff together it helps. I appreciate you guy's taking the time to help me out.
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Most of us have been there. Many of us are self taught and survived. If you like to read. you will do fine. :)
 
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