CPM 3-V hardness

S

Steve Beckwith

Joined
May 29, 2004
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What hardness should I use with CPM 3-V in an axe that is 36" long, with approximately a 15" cutting edge, strong 1/4" thick. I'd like for this thing to be able to split wood among other things. Thanks, Steve B
 
1/4 inch thick steel is going to make marginal axe, not enough weight and thin for appropriate taper of bit.

If you are expecting to split wood use an axe.
 
I know that but that is not what I am asking. This is a custom piece for a friend and it is what it is. This axe is for splitting heads, not wood BTW. It is finished and ready for heat treat.
 
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Steve Beckwith said:
What hardness should I use with CPM 3-V in an axe that is 36" long, with approximately a 15" cutting edge, strong 1/4" thick. I'd like for this thing to be able to split wood among other things. Thanks, Steve B
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Low temp or high temp temper?
58-59 HRC for high temp, 60-61HRC for low temp temper. Don't go beyond 61 as toughness dips considerably. Almost D2 zone.
 
JoeBusic said:
Low temp or high temp temper?
58-59 HRC for high temp, 60-61HRC for low temp temper. Don't go beyond 61 as toughness dips considerably. Almost D2 zone.
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Not sure where you got that from. It just didn't sound close to me, and when I checked, 3V at 62HRC has about 25ft lbs, where D2 at the same hardness will have no more than 5ft lbs, according to the data provided by L Thomas in his book. And I personally wouldn't use the high temper especially for that application, as it increases wear resistance (a little bit), but really decreases toughness by robbing the steel matrix of carbon to make those tempering carbides. Take a look at the data and videos Nathan Carothers did with impact performance on 3V with low vs high temp tempering.
 
The sweet spot for 3V seems to be below 62. I've tried higher, but I haven't had any luck. That Bluntcut guy might have a process for it, but I don't.

I've come to realize that getting the low temp tweaks to work with 3V is not always easy for everyone. The low temp tweaks are, objectively, significantly better. But it isn't fool proof.
 
Nathan the Machinist said:
That Bluntcut guy might have a process for it, but I don't.
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It seems he was going for low temp Bainite formation. As he never displayed the aust temp, I guess he was going for more carbon in solution and with low bainite avoided an plate martensite. Also I found some research on low temp bainite and it really looks very good for toughness sake in knives. Just nobody made an edge retention test to see how that goes.
But the time it takes is subjectively long.
 
After creating this thread I looked around. This is what Crucible says:

"Recommended heat treating for the best combination of toughness and wear resistance:
Austenitize 1950°F (1065°C), hold 30/45 minutes, temper 3 times at 1000°F (540°C), aim hardness 58-60 HRC. The higher austenitizing temperatures can be used to obtain higher hardness, at a slight decrease in impact resistance. The lower austenitizing temperatures provide the best impact toughness."

I guess I will be using Peter's to heat treat, hopefully they can dial this in.
 
For what you have the industrial standard high temper heat treat is fine. It is not like you are going to grind the bevel to a straight razor. If you loose some edge stability it will never be noticed in your project.
 
Nate is the 3V guru, but the first knife I made was a 5" blade of 3V in 3/16" stock; I sent it to Paul Bos for HT back when he was at Buck and he said 60 was optimal.
 
Originally we planned to have it water jet cut but I ended cutting it with my side angle grinder. It took about an hour to cut, another half hour with an 80 grit belt. The original profile weighed 6.25 lb, between grinding the bevels and drilling the handle it is right at 4.65 lb. I had never ground anything that long or that heavy before. Canvas micarta scales are going to bring it back up to about 6lb.
 
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