Pesky hole in HT foil......decarb

Kentucky

Kentucky

Joined
Dec 13, 2008
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Every so often no matter how well we check our HT foil some way a pin hole finds its way into the foil. So after heat treat you have a spot of nice dark black decarb :mad: Just curious when this happens to you, do you just grind the decarb away or does that black spot of decarb make you throw it away? The first time that happened to me I got worried and kept the knife for testing. After I ground that few thou of decarb away(just a spot along the edge) it seemed perfectly fine and tested fine..Which made me think I redid a whole knife for nothing...Another post got me thinking about that and I just thought Id ask..
 
Clean it up and keep going. The surface is carbon depleted, but that doesn't go very deep and grinds away easily.

If it was an extreme case, and it was on the edge, I'd test the edge before I sold it to be sure by carving slivers off a nail along the length and see if the spot rolls differently than the rest of the edge. But I'd be real surprised if there any difference at all because the cutting edge is buried in a lot of steel that gets removed when you sharpen it and decarb is pretty shallow.
 
I'm with Nathan. People worry about decarb way too much. Surface colors and dark/light areas are just part of HT. Sand it down to smooth white steel and you likely have removed all decarb. Refine the edge to the proper thickness and sharpen and you surely have removed any decarb in the cutting part of the blade. Of the 100 things that can affect a blade's performance and quality, decarb is 99 or 100 on the bottom of the list.
 
That's about what I thought also..Ive had it happen a couple of times but always just ground it away. My own fault for trying to use too small of a foil packet.
 
This just happened to me today on a TEST KNIFE, how serendipitous.

The measured hardness all over the knife, both in areas where the 309 foil had welded to the blade and had to be scraped off and areas with a lot of black scale all measured the same within half a point.

The worst of the decarb was on the very edge.

I tested the blade thoroughly chopping and carving on osage orange, carving slivers from a large nail and finally chopping up a bunch of nails along the length of the edge. There was no noticeable difference in edge retention, roll, chipping or mushiness anywhere along the length of the edge. The surface decarb has no effect on the performance of the edge.
 
A surface grinder will show straighter sparks through the decarb layer and busy sparks with the base steel. It's usually only about .001 thick.

Hoss
 
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