Reply To: Hardness of steel rod…

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david pierce
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Tom, Bob,
I have a personal rule of no open flames inside my house. This especially includes welding or anything else that involves a tourch. I clear an open space on my driveway and have a large fire extinguisher on hand. When I was experimenting with NAPTHA as a cleaning solvent in my ultrasonic cleaner, I took it out to my driveway and used it there first. When I do it now (inside) I still put it in a sink just in case.
Oil can and does sometimes flame when a red hot piece of steel is dropped into it. I recommend a fairly heavy metal container that will not easily tip over plus a metal lid to cut off the oxygen supply if the oil should flame up. If your are holding the part with your pliers you don’t want to accidently knock the can over when you are swirling the part around in the oil. A cooking pot with a lid will work. You can use pretty much any oil however peanut oil does not smell as bad as nasty motor oil when it is used for this purpose. The tempering can be done in a toaster oven if you want a little more consistancy with your temperature control.
By the way. You said that your rod was S7. S7 is an air hardening steel. The material is designed to give its best performance when hardened this way. All you have to do is heat it to the proper temperature (1700-1750) degrees and then blow air on it. All of the expensive materials that went into making this steel give it this property. We used to heat air hardening tool steel in a small gas furnace after sealing it in stainless steel foil. When the proper temperature was reached the foil was removed and the part was cooled with a small pedestal desk fan.