Imperfections after HT

D

David R Davis

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Jul 30, 2018
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As you are probably well aware I’m fairly new at knife making. But here is my issue. I’m using 1095 steel, heat treating in paragon oven at 1500, using 100% argon for oxygen free environment, and queching in sewing machine oil (just happened to have several gallons laying around). Knives are worked down with 320 grit and cleaned with acetone prior to HT. After quenching hardness is tested with a enco Rockwell hardness tester, most are at 60-62 hrs. Tempered at 400. I don’t really have any scale, knives come out fairly clean. What is causing the small imperfections on the blade?
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Last edited:
valknut said:
1095 needs a faster quench medium like parks 50. That could have something to do with it
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Ditto. While Parks 50 is recommended for 1095 I've had good success with Canola oil. If you can afford it, get the Parks. If not you might try the Canola oil.
 
I started using canola oil but was having trouble getting the hardness. But also at that time I wasn’t using the argon and had more scale than I liked. So I thought I would use the machine oil. Most of the time I’ve been good at getting about 60 RHC, though about 25% of the time I only get 40-45.
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1500 is a little hot for 1095.

Also, your mention of scale leads me to wonder if you're trying to avoid grinding post-heat treat.

After HT, you should be grinding the blades a bit more to remove any scale, decarb or any other undesirable effects of the HT process.

And the need to be ground.....not just polished to shiny.
 
Well, I tried using foil to minimize scale, but I couldn’t unwrap the blade fast enough, since I had bought the ht oven used and it was configured for argon, I took the bottle off my TIG. After shaping (grinding, hand sanding) the blade, going back to the 2x72 grinder after ht created more mess that had to be trued back up by hand sanding. I’m not trying to go to polishing after ht, still hand sanding to to get where it needs to be. But back to the original question, what is causing the small lines/imperfections on the blade surface?
 
looks like decarb or some other normal stuff that happens when you heat a blade red hot. i think you need to leave the blade a little thicker and less refined before heat treating. you wont waste time getting it nearly perfect and then wasting more time by having to fix things post heat treat. that way you will be forced to remove more metal after HT and that funky patterns on the blade will disappear as well.
 
I was answering your original question. If you didn't go back and grind the blade significantly after HT, there's no telling what the imperfections on the blade are. Ruling out scale, decarb or other HT artifact by grinding is step one.

Don't waste time and steps getting a blade nearly finished prior to heat treating.
 
Two things similar to J-doyle's response.
1) Rc60 out of the quench is WAY too low. It should be Rc 65-66 with 1095. Read on as to why your test is probably wrong.
2) You don't mention cleaning up the blade. The argon may cut down on scale, but you will still need to grind off the decarb - which will be less, but still there. If you did a hardness test without grinding a clean and smooth spot on the flat tang, the reading will be incorrect.

To test a blade as-quenched, grind a small smooth and clean spot on the tang. Test in the middle of the spot. A 1X1/4" fine Cratex wheel in a flex shaft or Dremel will do this fast and easy.
The surface of a freshly heated and quenched blade can have all sorts of patterns on it. The photo wasn't clear enough to see what your issue is. Grind the bevels clean to 220 grit and if there are still any issues, that is more of a concern.
 
I appreciate all the responses.. I have lots to learn. The links provided by Ian F. Are probably what is happening. But according to Stacy Apelt and J-Doyle , John, I’ve been to cought up in getting the blade to look good prior to heat treat. I have been waisting way to much time there. Also hardness testing incorrectly. Yesterday I had thoughts about that. I had been working on a blade most of the day and wasn’t very happy with my results. Then After HT I tested a blade and it was in the high 40s, and I might have got a little upset and slammed it against my anvil, and of course it broke. I think I’ll grind off a spot on the broken blade and see how the test changes.

Thanks again
 
Shealding gas does not prevent decarb just scale. At high tempatures the carbon in the steal turns into a gas and leaves the surface of the steel. But yeah 60rc as aquenched is WAY WAY to low for 1095.
 
Well I’m going to take your all’s recommendations. This evening I heat treated three blades at 1450 and quenched them in canola oil that were about 75% ground. Initial testing on one blade had a hardness of 64. So far so good. Tomorrow I’ll temper at 400 then in the next few days, finish grinding.
 
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