Blotchy ferric chloride treatment with 1095

Frank Hunter

Frank Hunter

Well-Known Member
I'm putting together a couple of hunting knives that I'm going for a darker color theme with, ferric chloride treatment on the blades to a dark grey and probably a cold blue for the bolsters. The steel is 1095 from Admiral, 1500 degree austenitizing temp with a 5 minute hold, 130 degree canola oil for the quench. Tempered twice so far at 375 for two hours each. This steel required an annealing cycle before I could drill it. The ferric chloride etch is turning out awfully blotchy on the flats of the blades with my 600 grit hand finish, and I can see with magnification that there are herringbone pattern like borders to the blotches. I'm guessing my heat treatment is to blame but I'm trying to figure out just where I went wrong.
 
Frank, did you clean the steel thoroughly? I had the same issue a while ago due to a quick de-greasing that didn't remove all of the oil from the blade. But then again, I didn't have any pattern other than blotchy circle-like blobs.
 
I have had similar issues. Beings I work mostly damascus I etch almost every blade.

I have found that when I get a blotchy etch, its normally one of two things.

1st ad in my case most of the time. Its left over decarb from heat treating that I didnt sand past. that was not fully removed before attempting to etch.

2nd, and less often.. The heat treat and or quench rate was not even throughout the blade. In that case Its not as much blotchy as is it etches 2 very different colors. and sorta blotchy looking In this case, I re heat treat the blade. and problem solved.

I dont know if either of these may be part of the problem. Just shooting from the hip and trying to help. If it was my blade I would go back to 400G and sand the heck out of one side of the blade and try a quick re etch to see if the blotchy look goes away or is less then before.

I do agree that you need a clean blade as well as clean/frech Ferric.. If its contaminated by anything. It can cause spotty looking etches. and or streaking and other issues. So bottom line, both can and will effect outcome of etch.

Hope this helps, your mileage may vary!

God Bless
 
Thank you both for the information. Here's an update with some photos. Shown is some rust from the ferric chloride, silvery-frost decarb from the quench in some spots on the hollows still, and the pattern on the flats. I'm degreasing the heck out of them (acetone then windex) and not getting anywhere. Makes me wonder what the unfinished hollows look like. Definitely two different regions in the steel. I'm guessing it's my heat treatment, does my recipe sound viable or am I way off the mark with this one?

P2050014.jpgP2050015.jpgP2050017.jpg

The third photo is with a quick wipe of "3 in 1" oil to bring out the contrast a little better. That's a fiber of paper towel, not a crack ;)
 
That looks suspiciously like a quench line, in the first image anyway.... the splotchiness on the flats looks like decarb, or could possibly be an auto-hamon... In fact, after looking at the images again I am leaning towards auto-hamon, 1095 likes to do that sometimes...

What mix are you using,how much is the ferric diluted? Is it fresh, or has it been setting around for a few years?

And on a side note, why are you tempering 1095 to only 375f? You need to go at least 50-75 degrees higher for a durable cutting edge, IMO.
 
I ran these all the way into the oil, not going for a differential quench at all. The hollows are just scuffed up with a 60 grit belt at this point to get the scale off...I was gonna experiment with finish on the flats before I risked grinding the edges too thin. The ferric is a 1-1-1 ratio of ferric chloride, distilled water, and white vinegar. Freshish is how I'd describe it...only had about half a dozen blades in the bucket and some test pieces with a volume of a little over a gallon. As for the temper, I may creep up on a 400-425 for these for the third cycle, I have done smaller knives at 375 and everything was excellent, bowies are typically 450. These will be my first two finished 5" blade hunters using this steel. Tell me a little more about this auto-hamon...haven't heard that term before.
 
According to my information 375f will leave a rockwell hardness of about 63, which will likely be a bit 'chippy'... 450f leaves them about 61-62 HRC according to my chart, which is still rather hard.
As for the auto-hamon, check out this thread: http://forums.dfoggknives.com/index.php?showtopic=17496
1095 is a very shallow-hardening steel, and it can be difficult to cool the thicker sections fast enough to get full hardness, especially in canola oil. This gives rise to the blade getting a differential hardening regardless of quenching methods. It's kinda cool, but can be a shock if you're not expecting it. You can either leave them as is, or quench them again with a faster quenchant (brine or parks#50) and the effect might go away... again, 1095 likes to do this, so you may be best off leaving them as they are and acting like you ment for it to happen... :)
 
Once you get it looking like you want it just be aware that the feric cloride finish is not durable and will wear off rather quickly with use. If you want a more permenant darkening look at parkerizing your blade. Midway USA sells two solution for this and it isn't really hard to do. I think the Zinc will be darker than the magnesuim one.
 
burchtree said:
That is decarb. Grind or sand it down some more and you'll be fine. :)
Click to expand...

I agree with burchtree from the pictures. However! I did have this happen once when I did a bad job in HT. The soak wasn't right so I had different hardnesses throughout the blade which gave me a blotchy look.
 
As an update, I took the calipers to the knives, picked the thicker one, and went to grinding one side of it. Seems to be improving but not entirely. I stopped while I still had enough knife left, and will re-heat treat with a faster quenchant. The hollows are definitely uniform, just the flats and ricasso area are showing some differential. If I'd have ground these to a scotchbrite satin finish I doubt I would have ever noticed so this was an interesting learning experiment. Thanks everyone!
 
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