Re: Heat-treating question
thomd
>Hi Thom,
>When I have done this, I saw no discernible color change.
There isn't any discernable color change because the steel is going through the transformation. It's just a colour that one gets used to with experience. Like counting beats when tuning a piano you can almost feel a pulse in the steel. I find this unreliable though because I do most of my work outdoors. So I only get good colour when it's turning dark and so one has the steel changing colour, the light falling, not very reliable. However, in better conditions if I hit a few with the magnet, I won't really need it as time goes by.
>And as you say the magnet is only good for .77% carbon steel (I think). Steels with more or less require more heat to get to critical. I guess the magnet will, tell you if you are under 1000F or over.
It's much more accurate than that. The magnet isn't related to a particular temperature like 1000F, it's related to the realignment that takes place just below the trans temp. For most steel you have to go 50 degrees more, or thereabouts. This is where colour comes in. You get non-magnetic, I stick it back in and I quench the moment I see a discernable colour change. That works for me. My ability to see a colour change seems to be about that extra nudge, but it might be different for another person. I would expect it to be something one could tell.
One good thing for me about the magnet, is that with propane forges it's not good to be looking in the fire all the time there is a lot of IR radiation. So you can just go to the magnet after a glance and you only have to look at it to see the colour change. Then the next time one does one, one can just do the same count. Really more a concern for people actually doing a lot of this kind of thing. Still my comfort level for hazards is pretty low.
>I'm just wondering if there is a better way. I bought a tempilstik.
Tenpilstik is very accurate as are the cones they use in furnaces, A little wax cone that slumps at the right temp. I don't know if people use them in a forge situation, I would expect them to burn up. It's different actually having a flame there vs. the kiln. Worth checking into. Templestick is good for tempering in your electric oven. Just to catch if the heat where your blade is, is actually what the knob says. The other way is just to run a cycle and read the oxide colour, start low and work up. You can't overtempter at low temperature, at least not from a practical perspective. By the way, that's another reason to use olive oil or something similarly benign for the quench since used trans fluid or whatever is not something I want burning off in the oven.
"I'm wondering if an infrared pyrometer would work and if any one has tried it."
I have heard that those who tried it in the past were disappointed. Maybe because the required temps are int he inaccurate range on the cheaper models. There are now a lot of them around at quite cheap prices, not to mention Harbor Freight. I would buy one just for mechanical testing and checking the house envelope.
Pyrometers are considered reliable. Though most of those seem to be used for setting the internal environment in ovens, including ovens for heat treating. Like folks will use a toaster oven for heat treating and just drill a hole in it for the pyrometer. Some thing with a forge. So it becomes a process control for the forge moreso than a means of ensuring the actual part temp.
"I know you've done quite a bit of this work. Is that what you use? A magnet? OR do you go by color? And how often must you fix something because it wasn't quite right the first time around?"
Right at the moment I am just trying to make useable tools. I think of it like buying cast steel at the flea market. I want each tool to be good, but they don't all have to be the exact same, and I don't have a good way to measure that. The last batch I did about 11 tools and one broke, which was a first for me. Another seems soft. The rest all seemed to have hardened off properly, and they went into the same tempering oven, so that should mean the overall result is pretty good. Those were done out of doors in the winter. with several inches of snow on the ground, very poor conditions, except for the extended low light. I knew it would be poor at some point becasue each blade was taking the oil temp up further.
Industrial heat treating is very repeatable. So one can absolutely program certain conditions and repeat them very consistently. There are, however, ways of turning inconsistent processes to your advantage and getting even better results. It's not logically comparable to this following example, but...: Compare the consistency of a drum sanded surface to the smoothness of a perfectly hand planes one. The drum sanded surface should be more consistent, it won't have plane tracks weaving back and forth over it, but in the end, which is a better surface. Don't get me wrong, I'm not making an artsy claim for an inferior performing blade being "better". I'm just saying consistency isn't the be all and end all. You can outperform the plastic processors just by digging a little deeper into the craft. As anyone who has used a Gransford axe of Japanese hand forged tool could tell you. Unlike hand cut dovetail, good heat treating is not slower than industrial heat treating. It's all over in seconds. Repeat heat treating is not always a bad thing. It can be part of a fairly foolproff process.
Adam
- PS I wouldn't want to do this over and over to a good quality carving tool in fear of grain/crystal growth.
I agree that's why I suggested O1. However it's not necessarily going to be a disaster. Good tools are presumably targeted at some audience, and changing their characteristics may well improve them in someone's mind. Jim Cumming FWW video in which he improves a blister pack chisel seems a more modest point of initial departure.
