HELP!!! Acid etch issue

[WaltE99]

Can someone explain what is going on in this picture? I have attempted to etch this blade (prior to stone tumble) in Ferric Chloride 3 times and this is what keeps coming out....always the same section of the blade. After the 1st time it came out like this, I took it back to the Scotchbrite belt and then cleaned again with denatured alcohol. Same result. So after this 2nd failure, I went back to 400 and 600 Trizacs, Scotchbrite, and alcohol. This photo is after this 3rd attempt. This isn't a glare on the blade, this one section just will not take the acid etch.

Not sure if this makes any difference, but I had several blades out of my last batch that I had to clamp between 2 pieces of aluminum during the 2nd temper to straighten. Once straightened, I didn't keep those separate from the ones that were straight to begin with so I don't know if this was even one of thoseView attachment 733195 .

Since one definition of insanity is to do the same thing over and over again and expect different results, I figured after 3 tries it was best to ask for help. Did I get bad steel? Or screw something up in heat treat or temper? I have enough trouble with hand/eye coordination, I sure don't need this kind of problem.

 

[kuraki]

I don't think you've removed all the decarb from heat treat.

 

[Josh Rider]

Your blade and ricasso are hardened, the tang is not.
That's my guess anyway.
Did you harden in a small forge?

 

[WaltE99]

Thanks. Stupid question here, but how do I know when I've gotten it all off? I just assumed that decarb was gone once you grind through the black scale and down into "fresh" steel, which I did.

 

[WaltE99]

Your blade and ricasso are hardened, the tang is not.

Thanks. So I HT in a kiln rather than a forge, so that means the entire blade was heated. I suppose I could have not gotten the tang into the quench fast enough. From your reply then, non-hardened steel will not take an etch, correct?

 

[Josh Rider]

It won't etch the same. Did you just dip the blade in the quench?
Oh I re-read your last post.
That's just a guess on my part,

 

[kuraki]

There are 2 layers of undesirable material on your blade after heat treat, the first is scale, it's the black flaky stuff. The second is the layer that leached carbon out and developed that scale. It looks enough like "good" steel it's hard to explain in words how it's visually different, but you'll begin to recognize it. Until then the easiest way is what you just did. Etch it. The light areas are decarb.

 

[WaltE99]

It won't etch the same. Did you just dip the blade in the quench?
Oh I re-read your last post.
That's just a guess on my part,

Thanks. I just got my oven recently and have now done 2 batches of O1 blades in it. The first batch I did in the oven was 4 blades, all but one of which were FC etched. No issues with any of those 3.

Previously I have HT'd in a small forge of sorts so the tang was not hardened and my recollection is that they etched fairly evenly. Those were 1084. Also, after the handle is completed, I always have to touch up the tang with a dab of FC on a QTip or small paint brush and it always takes the etch. In the case of this blade, there is virtually no etch in the affected area.

Can I put this blade back through HT and temper? Do I have to normalize first and if so, how many cycles?

 

[WaltE99]

There are 2 layers of undesirable material on your blade after heat treat, the first is scale, it's the black flaky stuff. The second is the layer that leached carbon out and developed that scale. It looks enough like "good" steel it's hard to explain in words how it's visually different, but you'll begin to recognize it. Until then the easiest way is what you just did. Etch it. The light areas are decarb.

Thanks. So in this case I should just grind the flats some more, correct?

 

[kuraki]

Yes. To avoid this from happening, I generally start grinding after heat treating oil hardening steel at 60 grit and probably remove .010-.015" per side post heat treat.

An easy check to see if I'm right, is to grind through a portion of that light area under your scales with a dremel and see if it etches properly.

 

[Josh Rider]

Kuraki is probably right based on the kiln heat treat and your history of etching blades. I ran into etching issues with different shades of grey when I started out, but that was in a propane forge and not in a kiln.
Didn't mean to throw you off.

 

[WaltE99]

Thanks to both of you! I had to go out for a couple of hours so am just now getting back to this. It makes sense because even though I thought I had gotten all blades from the batch straight, this one still a very slight warp that I could (or thought so) grind out. What you don't see in that photo is that at the butt end of the blade on that side it did etch just fine. However, on the other side of the blade, the problem area is at the butt end and the center etched just fine, i.e. it's just flip-flopped. I'll just grind the flats a little bit more and see what that does. It's a small fixed blade EDC so I should have a little room to work. Thanks again!