Just finished my first SS heat treat. Comments? Advice?

Self Made Knives

Self Made Knives

Well-Known Member
Came home from work last night and fired up the oven. Followed Ken's posted Sandvik info for 14c28n and brought temp up to 1975. Wow! That's hot! I've been using O1 up to know and have never had it higher than 1500 degrees. That extra 500 degrees makes it a big difference. Blade was finished to 600 grit and at pretty much final dimensions.

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I used one of BossDog's pre-made foil packages and double creased it on the open end, getting as much air out as possible. I put a small strip of paper in the package too, seemed like a lot of people think it helps. When I put it in the oven, I immediately noticed/heard it crinkling. Didn't think that much about it, until 12 minutes later when I opened oven to get it out. Foil pack had ballooned up huge, making it kind of hard to get between quench plates. I just jammed then down as hard as I could, as fast as I could, but the foil wrinkled up a lot.

I think it still quenched fast enough, even with the wrinkled foil, but I was disappointed when I opened the package. My blade was pretty dark. It was even all over, but I wasn't expecting this much heat treat patina. Maybe it was caused by the strip of paper? Actually, the strip of paper was still whole, kind of like char-cloth, so I don't think it had much oxygen present. Is this much patina normal?
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I checked it with a file in one of the lightning holes, and it seems super hard, file wouldn't touch it. Did a dry ice and acetone cryo on it next. Found dry ice at a grocery store for $1.29 a pound, bought $8 worth, but probably only need about $2 of it. Oh well, the kids had fun with the rest of it! Put a thermocouple right on the blade to check temp, easily went below the -95 degree spec.
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Tempered it at 400 deg for 2 hours, so I'm expecting a harness of about 60 or so. Don't have a way to check it. See anything wrong with my procedure? Is the blade supposed to come out that color? Comments and advice needed, I want to get this right for next time.

Anthony
 
I'm not up on Sandvik steels but all my 154cm, S35vn, 440 or ATS34 blades come out with a slight electric blue and pink oxide, very slight. These are always 95% done blades, usually just a quick clean up with the last grit used does the trick. I didn't see mention of a pre-soak, which I do. I'm betting that the envelope blew up because of the expanding air at that high heat which may have compromised the seal. I use cigarette butts from my ashtray to burn off the air but paper is good too. For this to work, you have to burn off the air before the steel reaches the temp at which it forms scale (around 1400+ degrees).....hence the pre-soak. I could be completely wrong but I also do blades for other makers locally and can't afford to mess up. I also make my own foil envelopes, just another thing to check out. Hope you get it sorted out.


Rudy
 
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Well, I wondered about a soak, but nothing I'd read seemed to mention it for this steel. I put the package in once oven was up around 1500+ and let it ramp to temp from there. I worried about it being in too long, but maybe that's where I messed up. My oven seems to take a long time to get up to temp, especially the 1975. Maybe I should've put it in from the start, anybody know for sure?
 
Rob from Canadian Knifemaker explained the double foil technique. In the first layer, pit a pinhole in the envelope by the handle. In the second foil package, put a pinhole in the opposite corner. This allows just enough airflow to prevent balooning, but not enough to cause decarb. I've done the past four batches this way, and it works very well. Thanx Rob!
 
Yeah, I think it you mentioned that in another thread a while back, but I only had the one pre-made foil pack so that wouldn't have worked this time. When I get a roll of the foil, I want to try that technique sometime. But, watching YouTube and everywhere else, I don't see the package swelling up like mine did, still not sure what I did wrong.

One idea I had that might have contributed to the problem is the size of the package. I'm sure Boss only has certain pre-made packs available to him, and they're probably not sourced by a knife maker, look at the dimensions. In order to get a pack that is long enough for a blade, it is also way too wide. My blade is only 1.5" wide, but the pack is more like 4" wide. I thought about rolling the top down, but I was afraid it would interfere with my quench plates. Might have had way too much surface area above the blade.
 
I doubt the foil pouch was too large, but I use foil and make my own pouches, just barely large enough to handle the blade. No room to spare, and sometimes I barely have room to make the double crimp. I put the paper in the pouch a couple of times and the carbon given off by paper sure does leave a nice almost black patina on the blade. It's just not tough enough for a final finish for the blade or it could look good. I quit using the paper, I didn't like the way the paper made the pouch balloon up - just as you mentioned.

By not having any paper in pouch, the blade comes out a lots nicer looking - I finish to about 600 grit then HT. Just a few swipes with sandpaper usually cleans the blade up nicely. Remember, you have a full 2 minutes to get below 1100F (per Sandvik).

Sandvik doesn't mention any pre-soak for HT'ing. The heat time is a function of thickness of blade - their view on heating was the same as cooling. Doesn't need any soak, just get the metal to required temperature and good to go. The Sandvik engineer agreed the way I put a mist of water on plates to cool a bit faster was a good idea, mostly for getting the plates cool enough to handle was the feeling I got from his response to my question about the water mist. As in "If it makes you feel good", but did say it sure wouldn't hurt anything.

Since Rex turned me on to Sandvik steels, and Calvin suggested 14C28N, the 12C28N has become my favorite SS. Not saying much since I've only used 440C other than the Sandvik steels.

Ken H>
 
Well, the patina on my blade is pretty tuff, I dropped back to 400 grit to get it off. Took several minutes to get it off. I doubt that it hurt anything really, just a pain. Like everybody, hand sanding is not my favorite chore, so I want to avoid this next time. Probably skip paper next time and make my own smaller pouch. Going to start scales today.
 
You can also give a shot of WDT-40 in the envelope instead of the paper. I do 4 at a time in the envelope. I do not go above that number. I pull the envelope out and cut the end off with snips and extract a blade with pliers to put on cooling blocks and top with another block.
 
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