Damaged knives

[jason]

OP chip not as bad as this
https://www.instagram.com/p/BvqI6lrnxIH/

What on earth did they do to it???

[jason]

I got the knife back. A little over a week as they were busy but I wasn't in a hurry anyway. Here's a before/after



[Instagram]https://www.instagram.com/p/Bv7FPj-hSUM/[/Instagram]

[URLtarget]https://www.instagram.com/p/Bv7FPj-hSUM/[/URLtarget]

[rayl1234]

Looks good though not much remaining core steel left below the cladding.

[Drewski]

Don't want to be hijacking this thread, but the title suggests it's open to others. Was just using my Matsubara b2 to cut up some yams on my edge grain cutting board and noticed a strange mark along the edge on only one side of the knife. At the top part of the mark, there's a small lip that catches on my fingernail. The edge on the opposite side of the knife looks normal. It's like a chip, but only on one half of the knife edge. Clicking on the image makes it a lot easier to see.

I know that to get rid of it, I'll need to take it to the stones, but I was hoping to hear if anyone has any insight as to what caused this, or if this is somewhat normal. I'm sure it was just improper technique, so I won't take any comments personally.

Was it there before you used it? Not that it makes a difference that it needs fixing

I don't think so.

[Rufus Leaking]

My guess is the chips earlier in the thread, the OP’s has its genesis in the original ingot. Interstitial malformation due to silica, hence the whitish appearance, and can only be corrected by taking the edge back down with some rather serious grit. I don’t think these abnormalities are due to any heat treatment, as those types of failures would likely be more serious, like the subsequent photo with the >1mm chip. The foundry processes are wrought with potential inconsistencies and I’d imagine that as many as 1 in 10 blanks are affected, and most are likely discovered and discarded during sharpening. I’d ask some of the knife makers like Mr Harner and Mr Carter for their opinion, as I think they’ve likely seen this very thing. I know that as a machinist, voids in castings were quite common, and I recall one incident where a guy in the shop was drilling a heli-coil insert into a tool steel based casting, and uncovered an intact ball bearing within the billet right on the surface, and it was explained that it was common practice to use recycled materials within the foundry to make up the ingot.

[Carter]

I recently did some destruction testing on a very closed to finished differentially hardened W2 steel blade and did find some areas of the edge that were more prone to chipping. I made a mistake in the earlier part of the heat treat and cooked it with the recipe for 52100, approx 15F lower in temp than W2 gets...realizing the error after the full time at the lower temp, I raised the temp to the proper level...was the blade damaged by approx 25 minutes at such heats??? Normally during the austenization process the blade is heated at temp for approx 12 minutes. I also hardened this blade to a very high level for W2, approx 65Rc. I then tempered this blade at a lower than normal temp, and was pushing the steel hard to get a higher Rc #....maybe I left it too hard. So, the testing....I broke the blade and the grain structure looked great. Doing the hammer and nail test....cutting 10 penny nails by hitting the spine of the knife, I did get some areas that chipped out perfectly semi-circle round from the nail, and in other areas, I got a slight wrinkle at the edge....I tested multiple areas, there was no consistent area as to where the more brittle steel was. I did some hardness testing and did see some areas at 67Rc and other's in the low 60'sRc. Now, it is hard to get an accurate Rc on real thin portions of the blade, so I don't put full faith in the test figures. Also, there are no real conclusions, other than the grain structure looked great, and next time I will temper the steel to a 62-63Rc, W2 seems happy there.

I know some blades are prone to chipping and whether it is a base metal defect, an issue with heat treat (like above), or maybe an area of the blade that got overheated during grinding post temper, who knows. I my experience, removing some metal via sharpening/thinning will reveal some better steel. Just my $0.02.