HT Questions: Decarb and Multiple Quenches

[Don Nguyen]

Hello all again

Yesterday I was quenching some chisels I was making. The tips would NOT harden! Aldo's 1084, warm vegetable oil, mellow red color (in dim lighting), back and forward agitation. After about 5 tries, I cut off almost an inch off the tip, and tried again. HARDENED, no problem. Was this an effect of decarb during the forging process? I am assuming that during forging, the tips would get to a bright yellow, maybe 5 times, at most 8 times. If it is decarb I'm dealing with, I'm kind of surprised at how easy it is to occur; I always assumed it was minimal without major, noticeable effects.

This brings me to another question. Am I putting any unnecessary stress on the metal or affecting it in a negative way when I'm quenching it repeatedly?

Thanks everyone in advanced. Sincerely,

-Don

 

[mete]

Decarb is a time/temperature thing ,in addition the atmosphre is another factor. You should be heating it in the neutral or reducing part of the flame . I don't think your problem is decarb ,probably poor temperature control.

 

[Salem Straub]

mellow red color (in dim lighting)

I think Mete's right, you should at least be using a magnet. Yesterday evening I was normalizing W2 in dim light, the steel when viewed in shadow had quite a bit of heat color to it (medium red) although a magnet definitely stuck to it. 1500 degrees can look orange in shadow. 1418 (non magnetic) can look bright red in shadow.

Also, if some decarb did occur, it would be very shallow- did you file test just the edge of the chisel, and if so, how many file strokes? It can take a couple strokes to get through shallow decarb to the hardened steel underneath.

Another quick note: if you are forging fairly small chisels, and the amount of stock reduction is not dramatic, bright yellow heats are too high for forging. Even when starting with large stock, when higher heat is necessary to move the steel, one should use lower heats when finish forging. Forging hand chisels at yellow heats will lead to grain growth, necessitating thermal cycling after forging to reduce grain size. Better to work at lower heats in the first place, then normalize at least once after forging for good measure.

 

[Don Nguyen]

Hmm. I'll keep a magnet to check with from now on then. I'm going to do some tests and record the results. I'll cut out and forge some small, thin sample pieces and then test them each with a different quench temperatures - then break them to peek at the grain structure.

I'll try this: one almost-dead red, another one at steady red, then plunge one in orange, and last a mellow yellow.

 

[Remyrw]

red and dull orange probably aren't hot enough. Most of the time it's visible as a light orange for me. It really does depend on the ambient light. I tried to do it on a very bright day with no shade near the forge and could hardly see any color but it was non magnetic. The problem was, of course, that I didn't know how much past magnetic it was, I just knew I'd overshot that particular reference point. I usually try to test as i think it's going non magnetic, where the bulk of the blade is there but the spine and ricasso aren't. Then I know what shade we're working with right then AND that we're close. I then even up the heat and bring it up a bit more and it's done. By not having everything non magnetic I know I haven't completely overshot unless the thinner spots were clearly way over temp compared to the rest, at that point I'd have screwed up. I haven't done that in a while, but I've got a blade or two around that I restarted after doing that. If I know what the non magnetic threshold looks like in my current lighting conditions I can also judge the actual temp I want for 1080 and 1084. I wouldn't try it with something that required higher temps or soak times, but when you're talking a minute or two at most between checking around non magnetic and finishing it's not tough.