I’m not sure there is one pat answer to that question because there are some heat treating processes which are not always economically feasible. But first, let’s consider what you might be getting for your money when you use a commercial heat treater.
Commercial heat treaters are in business for one purpose… Making Money. Most commercial heat treaters have large or medium size furnaces and they must have a sufficient volume of metal in that furnace to justify turning it on. Thus, if you send them 2 lbs or 100 lbs of A2 tool steel, they may not be able to justify running the furnace until they have 300-400 pounds collected. So delivery time becomes an issue.
But worst yet, is if the commercial heat treater is not quite ethical, they may load your A2 tools, which require 1775F, in with some S7 that requires 1725F and D2 or H13 which requires 1850F and heat treat all at 1825F. What that does is over cook your A2 and S7, resulting in a low hardness and excessive retained austenite, which they fix by freezing in a mechanical freezer to –150F. That transforms enough austenite to martensite to get by and raises the hardness back to an acceptable level. But even though the hardness reads fine, the grain structure is not correct and the tool’s life is affected. The D2 and H13, on the other hand, are not quite cooked enough, which means you are missing all the carbides the steel could offer because they did not get into full solution during the soak. Again, the deep cold will bump the hardness up to acceptable levels but, again, your tools will not wear as long as they should and may even chip easily.
So far we haven’t even discussed the various sizes of the parts in the mix. A2, D2, H13 and S7, plus other air hard steels, require a soak at austenizing temperatures of 1 hour per inch of cross section. So, if the load contains small parts and larger parts, they must heat treat based on the size of the larger parts in order to get any hardness at all. This over cooks the smaller shape parts and again using deep cold they gloss over the problem and fool the customer.
Next is tempering. Tempering should be started once the metal is quenched to below 150oF, and never allowed to reach room temperature and if it does absolutely should it never be allowed to sit at room temperature for more than 2 hours before the tempering begins. This is something that happens very commonly at many commercial treaters. It is so important that from a mill stand point a piece of steel that has been allowed to sit longer than 2 hours at room temp should be annealed and re-heat treated because that much damage; that much life has been lost. And, all steels require a minimum temper of 2 hours per inch of cross section. This does happen in some reputable commercial shops, but, again, is a major value concern if it doesn’t. One hour of soak is not sufficient because the entire mass does not get to the tempering temperature.
Please remember, most commercial heat treat companies hire lower cost workers to actually handle your parts during the processes, normally with little or no supervision. Having visited over 100 commercial heat treat shops in New England, NY and NJ, I’ve only found a small hand full that actually have their act together and the life of your tools and parts are in their hands.
No, I’m not against all commercial heat treaters. There are good ones out there, but often they are hard to find without a lot of evaluation. And there are times that you will need them when specialty processes can’t be done in smaller in-house heat treat equipment. But it’s wise to be careful when choosing or specifying the use of a commercial house. A machinist can work for days to make a tool that can be ruined in a couple hours by a poorly controlled process.
With a Cress Heat Treat Furnace you can take control of your own destiny as far as heat treatment and turn around time is concerned.
COPYRIGHT © September 2007, by Advisor In Metals
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