A question about Delta 3V

Twindog said:
I had a reblade heat treated by a knife maker known for using A8(mod). The idea behind using that steel was to allow the knife to do some light chopping of branches, which -- because of uneven grain changes in the wood -- can create some severe stresses along the edge.

All the maker had was a small scrap of A8(mod) that was barely large enough to made a 4-inch blade. I asked about the grain direction, and was told it was OK, but I now have my doubts.

Using this super-tough steel in the same way as an exactly paired blade with the same geometry and shape in Vanax (both replaces for a Benchmade Rukus 610), the A8(mod) failed and the Vanax did not.

Here's a shot of the A8(mod) blade <60 Rc that chipped, but also cracked along what seems to be (although I really don't know for sure) poor grain direction.

2v2HtjqHGxAWtWs.jpg
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Gently increase the secondary bevel by 5 degrees. Try that, if it's still chipping maybe add more thickness behind the edge. Then add another 5 degrees, until the edge is strong and stable.

It's difficult to tell by the picture, how acute of the secondary angle is it? Looks thin.
 
Crag the Brewer said:
Gently increase the secondary bevel by 5 degrees. Try that, if it's still chipping maybe add more thickness behind the edge. Then add another 5 degrees, until the edge is strong and stable.

It's difficult to tell by the picture, how acute of the secondary angle is it? Looks thin.
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It was thin -- 15 thousands behind the edge, 15 dps edge angle. It was exactly the same for the A8(mod) and the Vanax. The Vanax (60 Rc) didn't fail. The A8(mod) did. And the A8(mod) should have been far tougher than the Vanax. But if you look at how the A8 failed, it doesn't seem right. I've never had a failure look like that. And it looks like an issue of grain direction -- at least to my mind what a grain-direction failure would look like.

The heat treater asked for the blade back to test. I sent it back, but he did not test it. He just kept the evidence.
 
Twindog said:
It was thin -- 15 thousands behind the edge, 15 dps edge angle. It was exactly the same for the A8(mod) and the Vanax. The Vanax (60 Rc) didn't fail. The A8(mod) did. And the A8(mod) should have been far tougher than the Vanax. But if you look at how the A8 failed, it doesn't seem right. I've never had a failure look like that. And it looks like an issue of grain direction -- at least to my mind what a grain-direction failure would look like.

The heat treater asked for the blade back to test. I sent it back, but he did not test it. He just kept the evidence.
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Kind of looks like you might have hit a rock? I agree, that is an unusual looking failure, if I'm seeing it right.

Are you sure that A8 is at 60? It might not be. Or, it may have been barely tempered to have retained that much hardness and be outside of its sweet spot. Under-tempered steel, even if it is at a reasonable rockwell hardness, often doesn't work very well. You have areas of highly tetragonal martensite. Steel can go up in strength slightly as it is tempered before it starts going back down.

15 DPS is probably too acute for A8 mod. Unless you were using one of those 15 degree wedges as your reference. And if the primary grind on your knife is 5°, and you add that to the 15° then you're up at 20° per side which is actually about right.

People don't want tough knives. People want durable knives and mistake toughness as durability. Just like they mistake wear resistance with edge retention.

Wear resistance is just one facet of edge of retention, edge stability being the other.

Toughness is just one facet of durability, strength is the other. Toughness and strength are often diametrically opposed attributes.

It's possible that the problem with your blade is too much toughness (too soft and weak) compared to the harder (stronger) alternative.

Toughness is just the amount of energy absorbed in a fracture impact. Dead soft steel is pretty tough.

A8 is good at not breaking. It would not be my first choice for a small blade not subject to breaking.
 
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Nathan the Machinist said:
Kind of looks like you might have hit a rock? I agree, that is an unusual looking failure, if I'm seeing it right.

Are you sure that A8 is at 60? It might not be. Or, it may have been barely tempered to have retained that much hardness and be outside of its sweet spot. Under-tempered steel, even if it is at a reasonable rockwell hardness, often doesn't work very well. You have areas of highly tetragonal martensite. Steel can go up in strength slightly as it is tempered before it starts going back down.

15 DPS is probably too acute for A8 mod. Unless you were using one of those 15 degree wedges as your reference. And if the primary grind on your knife is 5°, and you add that to the 15° then you're up at 20° per side which is actually about right.

People don't want tough knives. People want durable knives and mistake toughness as durability. Just like they mistake wear resistance with edge retention.

Wear resistance is just one facet of edge of retention, edge stability being the other.

Toughness is just one facet of durability, strength is the other. Toughness and strength are often diametrically opposed attributes.

It's possible that the problem with your blade is too much toughness (too soft and weak) compared to the harder (stronger) alternative.

Toughness is just the amount of energy absorbed in a fracture impact. Dead soft steel is pretty tough.

A8 is good at not breaking. It would not be my first choice for a small blade not subject to breaking.
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Thanks, Nathan. You might be right. I could have been too soft. The A8 was supposed to be hardened to 60 Rc. But after the failure (hitting a green, free hanging branch, not a rock) I tried to figure out what the hardness was, suspecting a bad heat treat, as you say. With an S30V blade rated by Benchmade as 58-60 Rc, I could easily scratch the Rc 60 A8 blade, but the A8 blade could not scratch the S30V blade. So I was pretty sure the hardness came in too soft.

With the Rukus S30V blade stock, it would microchip a bit when chopping small branches hanging over the trail. But it was early S30V that often did chip a bit as makers tried to dial in the quench rate. A8 at 60 Rc should have been tougher (more resistant to chipping) by a lot, and just as strong, if not stronger. Only wear resistance should have gone down.

I've been whacking branches with my Vanax blade for many years, with no chipping.

Well, maybe it was heat treat. But those straight parallel cracks in the edge make me think grain orientation.
 
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Delgadonine said:
After reading what Nathan wrote, anyone else feel like an apprentice?

Thank you for your responses Nathan.

Tied for first place in my next purchases: a Carothers and a Winkler.
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A few years ago, I took my CPK Light Chopper out to clear some old-growth salmonberries and give my newly planted redwoods a fighting chance to catch a little sun.

That knife was amazing. After a couple of hours chopping, I could barely tell I'd used it. It's not just the steel. It's everything. The edge that Nation puts on it lasts and lasts. The only other time I had an edge last that long was one that Jerry Hossom sharpened for me. Some knife guys just know how to make an edge that lasts.

And the handle of that knife is perfect. The balance. I kept stopping every 20 minutes or so just to look at and admire that knife. Nathan puts a lot of thought into every aspect of his knives. It really shows.
 
Twindog said:
A few years ago, I took my CPK Light Chopper out to clear some old-growth salmonberries and give my newly planted redwoods a fighting chance to catch a little sun.

That knife was amazing. After a couple of hours chopping, I could barely tell I'd used it. It's not just the steel. It's everything. The edge that Nation puts on it lasts and lasts. The only other time I had an edge last that long was one that Jerry Hossom sharpened for me. Some knife guys just know how to make an edge that lasts.

And the handle of that knife is perfect. The balance. I kept stopping every 20 minutes or so just to look at and admire that knife. Nathan puts a lot of thought into every aspect of his knives. It really shows.
Click to expand...

Id like to see a picture of Your redwood trees.
😁
 
Twindog said:
A few years ago, I took my CPK Light Chopper out to clear some old-growth salmonberries and give my newly planted redwoods a fighting chance to catch a little sun.

That knife was amazing. After a couple of hours chopping, I could barely tell I'd used it. It's not just the steel. It's everything. The edge that Nation puts on it lasts and lasts. The only other time I had an edge last that long was one that Jerry Hossom sharpened for me. Some knife guys just know how to make an edge that lasts.

And the handle of that knife is perfect. The balance. I kept stopping every 20 minutes or so just to look at and admire that knife. Nathan puts a lot of thought into every aspect of his knives. It really shows.
Click to expand...

Man, I really appreciate that, thank you.

I'm going to go out on a limb here and speculate that it held an edge really well, not because I'm super good at sharpening but perhaps because of the steel and heat treat. Which, at this point, are damn near witchcraft. 😁
 
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