Any ideas what is wrong with this blade?

J. Hoffman

J. Hoffman

Joined
Jan 1, 2011
Messages
1,798
This is a chefs knife I'm working on, and I've been progressing through the different grits of hand sanding. On each level of wet sanding (using Mobil 1) I get this band of discoloration in the blade. The band is perpendicular to the edge and about 1" wide. The band is only visible when wet sanding, and as soon as you wipe away the sanding slurry the band goes away. The band is on both sides of the blade. It can not be seen at all if the blade doesn't have the sanding slurry on it. I cleaned the blade and did a quick FC bath, and the band did not show up in the etch. I can feel no difference in the blade. I thought maybe I would be able to feel a dip, but it seems as flat as can be. I tried taking a file to the edge and the file skated the entire length of the edge. I thought perhaps this area had not gotten properly HT'd. The HT was a salt bath for both high and low temp. Any ideas what this is? Is it going to come back to haunt me?2013-11-01_20-31-09_10.jpg2013-11-01_20-30-58_685.jpg2013-11-01_20-31-37_558.jpg
 
PT Doc said:
Maybe an odd magnetic field that arranges the slurry oddly?
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That almost makes sense, because the band isn't evident until you have a good slurry. The plain oil doesn't show the band, and it doesn't show right away when you first start with a new grit. Is it possible to have only a section of the blade be magnetized?
 
Mooseyard said:
That almost makes sense, because the band isn't evident until you have a good slurry. The plain oil doesn't show the band, and it doesn't show right away when you first start with a new grit. Is it possible to have only a section of the blade be magnetized?
Click to expand...

Your sample would not be the first with this ghosting. Steel can be magnetized by the way it gets worked so my guess is that your piece is such an example.
 
I took a small round magnet and touched it the metal in the area of the band. I went back to wet sanding at now the marks are round circles the size of the magnet. That makes me happy.
 
Take a magnet, a rather powerful one if you have one, and stroke it from one end of the blade to the other about 20 times. Make sure to wrap in toilet paper to keep it from scratching the blade. This is how I magnetize screwdrivers and it will also work on knives. Then let us know if the banding disappears.
 
A demagnetizer coil is a very useful shop tool....especially when you use grinding magnets.
 
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