Cracked

[SteelSlaver]

I have an order from a couple brothers for 2 D2 sharp finger style knives and 2 of my D2 drop points. Because these sell well and things happen I started out with 3 blanks of each. Good plan because after finishing the drop points to the point of being ready for scales I was working on the sharp fingers and one of them had a "scratch" running down from the spine that wasn't coming out even when I went back to 220. Finally I took it back over the the grinder with a A65 belt and it didn't go away then either. Something about the scratch had said crack even before I went to the grinder. I took it to a vise and clamped it with some hardwood pads by the scratch and pulled on it with a bit of force. Snap. Sure enough it was a crack. The steel was maybe 1/8" thick at this point. The crack was a light brown and about 1/2 way (1/16") through the steel and about 3/8" down the blade and made a semi jagged triangle. The rest of the steel was good with real fine grain. This is Bohler K110 D2 and I have a lot of it and never had a problem like this with it. I am glad I saw it and broke it and the knife never left the shop.

The brown color has me thinking the problem have been some kind of an inclusion in the steel? There is also a tiny spot of the brown slightly away from the main part. Really has me wondering.

Standard heat treat. 1500 soak then 1850 for 40 minutes then quench between cold aluminum plates, then dry ice slurry followed by 2 tempers at 425. All came out straight and none needed any straightening. The other 5 knives seem fine, sanded out and polished up well.

 

[quint]

I think the brown color is just corrosion basically. I know every single crack Ive found if I let the blade sit for a while (like I dont get to sanding it for a couple of days) then find the crack and snap the blade it will either be a darker grey to blackish color or a brownish color. Depends on what I have done to it also, if I have etched it then it shows blacker. Kind of cool in the fact ya can see how far the crack went into the metal, ok not cool because it sucks finding a crack after hours of hand sanding.

 

[Omega Leather Works]

Quint, would that corrosion happen with stainless (or close anyway)? I've been able to patina d2,but it took some doing. I know most stainless can corrode, I'm just wondering what would cause it under normal circumstances.

 

[Stacy E. Apelt - Bladesmith]

The darker color would indicate that it had been in the steel during the HT. It could have been an inclusion, a stress crack, or just a plain old flaw.

 

[SteelSlaver]

I tend to think along the same line as Stacy. Lean more towards some kind of inclusion because of the stainless envelope and any HT color I get in D2 is a grey or slightly bluish. I guess I will just write it up to stuff happens and keep an eye on tiny scratches that don't sand out. Sucks to get one that far along and lose it, but way better than having it go out the door and have it break on a customer. Even replacement wouldn't completely fix the damage that could do. I have sold a bunch of D2 hunting knives basically by loaning one to a friend I was hunting with to clean his deer when his knife wasn't "cutting it". He told friends who bought and they told friends etc and it has just kept spreading. That one knife has sold another 40 or so. Mostly they like the edge retention, then nice scales and finish. I always send a note that D2 is on the brittle side and not to pry with them, but, a knife that broke of short could really hurt a guys reputation. A broken tip not so bad.