Call for Charpy toughness samples

hugofeynman said:
Can’t remember, Larrin, did Warren went down to 57hrc with 8670, where it has even more toughness?

How amused I’ll be if this “simple” steel reveals to be tougher at 60hrc than 3v at that same hardness, no matter the way it is tempered (high or low temper)!
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I just did the two samples. I thought I did more, but the more complete sets of samples evolved later in the process. The charts said that sample should have been Rc56, so I will do more tempered even higher, as well as lower to see where the toughness takes a nose dive.
 
Willie71 said:
I just did the two samples. I thought I did more, but the more complete sets of samples evolved later in the process. The charts said that sample should have been Rc56, so I will do more tempered even higher, as well as lower to see where the toughness takes a nose dive.
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Very good, Warren! Let’s take that steel to his toughness limit!

Have you re heat treated NZ3 already? Take your time!!!! Just curious about the hardness it can reach and even more with the toughness numbers!!!!:)
 
Simplified table:
toughness-table.jpg
 
The problem that I have seen with 8670, at least from our knife maker sources, is the lack of stock over 5/32. It also seems to be a bit more pricey than say 80CrV2 or other simple steels.
 
One extra size would be good and, of course, cheap would be better. :D
 
hugofeynman said:
Very good, Warren! Let’s take that steel to his toughness limit!

Have you re heat treated NZ3 already? Take your time!!!! Just curious about the hardness it can reach and even more with the toughness numbers!!!!:)
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Nz3 is out for grinding.
 
jdm61 said:
The problem that I have seen with 8670, at least from our knife maker sources, is the lack of stock over 5/32. It also seems to be a bit more pricey than say 80CrV2 or other simple steels.
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8670 is available up to almost 1/4”. About 0.224”. https://www.alphaknifesupply.com/shop/8670-carbon-steel

I think you are referring to 15n20, which is only available up to 0.130”.

80crv2, 15n20, and L6 are out for grinding. Getting this toughness data will be very interesting. We also have W2, 1095, 1084, O1 and 52100 in multiple conditions to compare.
 
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No, referring to 8670 not being available in sizes larger than that 7/32. If you get it from Admiral, it appears to ONLY be available in 3/16.
Willie71 said:
8670 is available up to almost 1/4”. About 0.224”. https://www.alphaknifesupply.com/shop/8670-carbon-steel

I think you are referring to 15n20, which is only available up to 0.130”.

80crv2, 15n20, and L6 are out for grinding. Getting this toughness data will be very interesting. We also have W2, 1095, 1084, O1 and 52100 in multiple conditions to compare.
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Willie71 said:
I’m finding mental comparisons interesting. 8670 is very tough, but at Rc64, it’s less tough than M2. M2 will have much better wear resistance. The right steel, in its sweet spot balancing toughness/hardness can be identified for the desired application.
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And CruForgeV is twice as tough at 64 Rc. Sometimes a higher carbon steel is tougher if at high hardness.
 
I bet 15N20 would be similarly tough to 8670. I wonder at what hardness the toughness drops off steeply, probably around 62rc, which would make it the sweet spot for knife application. Another comment, I've used M2 at 64 rc and it was not chippy at all, easily adequate for kitchen knives, so perhaps we shouldn't be so awed by big absolute numbers and pick an adequate toughness, which may be a lowish appearing charpy score.
 
Larrin said:
And CruForgeV is twice as tough at 64 Rc. Sometimes a higher carbon steel is tougher if at high hardness.
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Then add in wear resistance, and z-wear really shines again. It is slightly tougher than 52100 or cruforgev at Rc61.9, but it’s double the wear resistance of 52100 based on personal experience.

This is fascinating stuff!
 
cotdt said:
I bet 15N20 would be similarly tough to 8670. I wonder at what hardness the toughness drops off steeply, probably around 62rc, which would make it the sweet spot for knife application. Another comment, I've used M2 at 64 rc and it was not chippy at all, easily adequate for kitchen knives, so perhaps we shouldn't be so awed by big absolute numbers and pick an adequate toughness, which may be a lowish appearing charpy score.
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I have a few cast cru wear kitchen knives at Rc63+. They hold up just fine. Tough enough for the application is all we really need. I have a kitchen knife in 8670 tempered at 175f, and the owner prefers it to his W2 knives at Rc62. Again, tough enough for the application.

What I’m taking from this, is that we are often leaving performance on the table. We can go thinner, or harder and still have surviving knives, especially if we stay in the steel’s sweet spot.
 
Warren, do you think that at 64, the 8670 is essentially "untempered?"
Willie71 said:
I’m finding mental comparisons interesting. 8670 is very tough, but at Rc64, it’s less tough than M2. M2 will have much better wear resistance. The right steel, in its sweet spot balancing toughness/hardness can be identified for the desired application.
Click to expand...
 
Quick update. Ive got the 80crv2 done, and a bunch more 8670. I’ll do up the chart later today. I’ve got some V4e and 4v done. I need to refill my dewar so it’s oil hardening and high temper until Monday, when I can make it into town. I’ve cut some more M2 and N690 coupons. I’m going to email my charts to Larrin, so he can add the charpy values, or he can send them to me so I can add the values.

It would be nice if we could set up an interactive feature, so the chart can be ranked based on steel, hardness, or toughness, so comparisons would be easier. I’m not sure if this forum can do that.
 
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