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Originally Posted by Manoel
Not sure if you already seen it, but Dave wrote one of his memorable posts about it a while ago. Here it is. |
Thanks for remembering the post, hopefully you will find it useful. Here is a little additional information -
If you do a water (instead of oil) quench for the hardening/tempering steps, you can improve the results and consistency of the hardening by using an appropriate surfactant in the water. As you quench the part, bubbles form in the liquid at the interface between the hot part and the quenching fluid. You want to move the bubbles away from the hot metal as quickly as possible, and and keep a solid surface of quenching fluid against the metal. The surfactant will break the surface tension around the bubbles, and allow them to quickly seperate from the metal and float free in the fluid. This will allow the fluid to restore contact with the metal, and lets it do its work cooling off the part. The "magic mix" that I use is 1/4 cup of Cascade dishwasher
powder per gallon of water. DO NOT use a liquid dish soap or laundry detergent! You want something with a low "suds content" that will not foam up when you stir it around (remember, we are trying to avoid bubbles here!).
If you are using a low-carbon or mild steel, you will want an alternative to the quench-and-temper process (which is really only effective on high-carbon steels like tool steel). For low-carbon steel you can do small-job case hardening (which will basically add carbon to the surface of the metal and increase its ability to be temperature hardened). Heat up the part until it is cherry red, bury it in a surface hardening compound, reheat it and cool by quenching. The compound (I use
Kasenit, available from MSC, and there are others) will provide a surface case hardening a few tens of mils deep, which should be good for most applications that we will run across. The case hardening will give you a harder surface, but the effect will not penetrate as deeply into the metal as the quenching/tempering process. You will have to figure out where you want to be in the hardness/depth trade space based on your application.
(note: there has been a lot of discussion recently in the hobby machinist community on this topic recently - if you can grab a few of the recent issues of the
Home Shop Machinist, there are some good articles that will provide additional information)
-dave