its back to drive me crazy

Gahagan

Gahagan

Well-Known Member
ok a while back I posted a question about some lines I got when etching my hamon that did not show up before the etch. http://knifedogs.com/showthread.php?36976-Perplexed!!!!-Flaw we chalked it up to carbon from htinng at a rougher grit. Well its back and I cant figure what it is. I sanded the blade to 320 before ht, put on the clay, hted, tempered, sanded to 800 grit and etched and these showed up all over the edge of the blade! What is it how do I get rid of it. You cant feel it and it does not show up until ethcing. When etched it turns white while the edge turns black. It is driving me crazy. I hate hand sanding to begin with and to have to do it over again is no fun.

 
Warren Krywko said:
Are you sure you sanded past the deformation in the steel from the courser grits fully removing the problem?
Click to expand...

My question also. I didn't read anything in your first post that mentioned any post HT grinding. There is likely some decarb after HT that hand sanding alone might not take care of.

Also............are you sure it's not some residue or oil left over from cleaning the blade prior to etching? I know it seems like if you have oil or acetone or windex or anything else on your blade before you etch it, it seems like the acid will etch that spot into your blade. Just a thought.
 
At the Southern Alberta Hammer In I discussed this exact problem with Kevin Cashen. I'm sure he can explain it better than me. The steel is distorted by the 36g belt grit, and when you sand or polish just enough to not see the grit marks, it looks fine until etched, but the etching reveals the distortion in the steel. If I got it correct, the steel needs to be ground with a finer grit beyond the 36g with max 120g. Finer grits will just polish the distortion rather than remove it. Hopefully he will come along and correct me of I'm wrong. I did as suggested, and it seems to work.
 
"sanded to 320 before ht, put on the clay, hted, tempered, sanded to 800 grit and etched"
I started out with a 50 grit belt and moved through the grits to 320 grit before ht. After ht and tempering I ground it on the belt starting at 80 grit and moved up to 320. I then moved to hand sanding starting out at 180 and went up to 800 grit. I then cleaned the blade and etched it.
 
"put on the clay, hted, tempered, sanded to 800 grit and etched"

Sorry. I didn't equate 'sanded to 800 grit' to 'ground' with a belt. :)

I've never seen anything like that with my own blades. Seems like once you described your post HT process more, it would most likely rule out decarb. I've seen some alloy or carbon banding in my blades before but it never looked like that. Then again, I'm no metallurgist either.

So I guess outside of something on your blade that got 'etched' in (and I've had that happen before and it etches in deeper than you would think), I'm out. Sorry to not be of more help.
 
I am going to take it back to the belt and work from 120 back up and see if it helps. This is killing me. Thanks for trying.
 
I've had this pop up from time to time too, my solution was a satin, unetched finish for that blade....:) I too would dearly like to know what it is, what causes it, and how to avoid it. Warren's post is the best explaination I've heard yet.
 
If the steel was hot rolled, somewhere along the process, scale or something else may have been pressed into the bar (?). It would be interesting to see if this occured through out the bar at that level if ground down. Sorry, no definitive solution. The closest I've seen was in a polished 5160 blade but those showed up as slightly darker "flakes" if held right in the light.

Rudy
 
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