Decarb pitting

J

jtwodogs

Joined
Feb 1, 2009
Messages
421
Let me preface this with a IMHO.
I am new to knife making and just wanted to share an experience so that others that are new may benefit. If you are new to knife making and......
1. Do not do your own heat treat.
2. Hand finish your knives.
3 You are working with carbon steel and not stainless.

It to me anyway is worth the weight of your knife in gold to find a heat treat company that has minimal decarb pitting.
I did put my blades back on the belts, but am not proficient enough to take them all the way down to a finished product without hand sanding, which with heavy decarb pitting is taking hours per blade.
 
From what I understand you can soften decarb with a soak overnight in vinegar. True it takes longer, but you're already wasting time grinding, plus it saves on belt wear.
 
I don't think vinegar will help this problem. It will have to be ground or hand sanded out.
Frank
 
A soak in vinegar will help, but a soak in sodium bisulfate will do better. Mix a cup or two of PH-Down (NaHSO4) in a gallon of water and soak for a few hours to overnight. Rinse well, scrubbing with a stiff brush, and then sand the blade down.

BTW, use plastic or glass containers to soak the blade and store the pickle solution.

All blades need to be re-sanded after HT.
 
I did not have to much problem getting the decarb off. The problem was the deep pitting into the blade metal that has given me the problem it is almost like I have had to re-profile the blade all over again. The HT seems to be spot on, but the deep pitting has killed me.
HPIM1192_zpsq6f93jou.jpg
 
I sent the blades off to be HT'ed. I sent 3 blades of 1084 and one AEB-L. I would rather not mention the HT company, the stainless blade came back excellent. It was the carbon blades that have given me the headache.
 
Just to be sure, you did tell the HTer that three were carbon and one was stainless?

Was the HT done by a company or just by another knifemaker?

Did you forge the blade or grind it?




In the photo, it looks like you just hit it with a fine belt. When you give this blade a clean up grind on a 120 grit belt, how does it look? I suspect you just haven't removed the decarb layer.
 
Yes, all blades were listed as to what steel composition they were.
It was a Company and not another knife maker, although I have already spoken to another knife maker who said they would be glad to do future carbon blades for me with very little decarb pitting.
The blades were ground from Aldos steel, before I sent them I finished with 220 grit.
 
I think there is some confusion going on here. Decarb vs Scale. Scale can be removed with vinegar and the like, but decarb??? AFAIK, the only way to get thru a decarb layer is to sand it out. As far as the pitting goes on the knife you have pictured.....I am thinking that is caused by the anti-scale coating the heat treater used. I noticed when using ATP-641, I get pitting similar to what you have shown.....not nearly as bad tho. Maybe the flux or whatever is in the anti scale causes it....I really don't know. But every time I use the product (which I LOVE BTW), I get small divots across the blade. They must be sanded out. The problem is even more noticeable to me if I do any thermal cycling with the ATP (which I have to re apply every cycle...the stuff blows off even in an air quench). Seems like the more cycling I do, the worse the pitting is.

Also looked like you got a bit of reverse sori from the quench. (in the photo the edge appears to drop as you approach the tip). I just quenched a 1084 chef's knife in P50, and there was a smidge of it detectable.
 
Again new to all this. But the 1st 4 I sent off to a different HT'er came back with minimal sanding to get them into shape, seems like I have been working on these blades forever
 
Stuart is right mentioning the 2 different faces of athmosphere issue during the heat treatment.

A great product for protecting carbon steel blades is PCB sold by usaknifemaker. I would recommend it to everybody HTing carbon steels, actually i don't understand why people use foil when working with SS and don't use PCB antiscale compound when treating carbon steels and damascus. It is scale proof and offers almost total protection against decarb.
 
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