Reground kitchen knife tip rusts quickly

B

BobJackson

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Sep 21, 2015
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I got a 1x30 sander a couple weeks ago, and today I figured I'd reshape the tip of a kitchen knife that I broke a while ago. It was a cheap knife, so I wasn't really concerned about screwing anything up. After fixing the knife, I put it in the sink with the other dishes and soaked them for half an hour before washing everything. After cleaning and rinsing the knife off I saw that where I had ground the new tip, it had already begun to show show speckled rust spots. There are no markings on the blade as to the type of steel, but I assume it's stainless. I always soak my dishes for a bit before washing them, and this knife has been through that countless times with no issues. Also, if it makes any difference, I re-shaped the tip with a fairly course belt, and was planning on going over it with very fine grit sandpaper in the near future.

Another thing I just thought of, I didn't completely clean the knife off before putting it in the sink. I wiped it off on my pants, but there was still a bit of ground/powdered steel magnetically stuck to the blade (the grinding dust was sticking to blade as I went along, and making little magnetic spikes of dust on the knife edge and spine). I just noticed that even a part of the spine that was never reground has some rust spots on it too. And one of the plates that was at the bottom of the sink ended up with some faint brown speckles on it after washing, like the steel dust had stained it.

Does anyone know what the problem is? Is it because I exposed new steel? The area I was grinding off heated up a bit while I was working on it. It was nothing extreme, but can this create problems? In any case, it's a cheap knife and I don't really care about it, but I'm just curious about why the rust is starting. Thanks in advance for any info.
 
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Hmmm ... being a 'cheap knife', it's probably just plated metal. You ground off the plating and exposed the rust-prone metal underneath.
 
What type of abrasive is on your grinding belt?
But my best guess is it was overheated. There is a whole explanation of "sensitization" of stainless I won't get into.
 
Rougher finishes also tend to rust faster as there is more surface area exposed.
Could be a few reasons, but I would polish it up and see what happens.
 
Based on what you've said, I'm guessing it was metal dust that rusted. Here's your experiment:

Clean the blade thoroughly preferably with something like a good degreaser or Bar Keeper's Friend... something that will guarantee that all of the dust is gone. Then soak it in the sink for half an hour again. If the rust comes back, something is amiss. If it doesn't rust, it was just dust.

Brian.
 
I know this is a really late reply, but I figured I'd add it just in case it ends answering a future question. I finally got around to trying to fix the rusting tip of the stainless kitchen knife I reground. I hand sanded the rusty bits off with a fresh piece of fine sandpaper (took about 2 minutes). Then I let it soak for a bit and then air dry, same as before, and now there is no rust.

The belt I originally used on the blade was first used on other things, which likely deposited grains on the stainless. So, problem solved.
 
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