Newbie Question On Heat Treating And Tempering

Joe Pitz

Joe Pitz

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Hi all,

I have seen images of various items that folks have heat treated and tempered here on the forum.
They have a blueish or brownish hue to them.

When I look at, let say, a new dead center, live center, end mill etc. The tooling is bright and shiny.

How then do you perform heat treating, tempering and then get the really nice finish back on the tool, without machining again?

Sorry, really newbie question.

Thanks

Joe
 
Most of the tools you are seeing were heat treated and then brought to finished size by grinding. Hence the bright finish.
After heat treating you can also use sandpaper or polishing compound to remove the oxidation from the part.
 
Jim, Thanks, but doesn't the grinding remove the heat treating? Or let me ask it another way, does heat treating only affect the surface of the tool or the entire
tool?

Thanks

Joe
 
When heat treating tool steels the hardness is all the way thru. Mild steels are usually only hard to a depth. And some steels need to be carburized in order to get a hard skin leaving the center soft.
 
The oxidation from running colors during the tempering process can be chemically removed as well. Hydrochloric acid will dissolve the oxide coat very quickly. A polish will then give a bright finish.
If tools are tempered in an oven with an inert atmosphere, there will be no discoloration. Tools are also wrapped in stainless steel tool wrap to prevent oxidation.
 
There are two forms of heat treating. If you are working with mild steel then any hardening would have been done as case hardening. Only the surface of the part has had the carbon increased and is hardened. If you are dealing with a high carbon steel or a tool steel, the hardening process will have hardened the part all the way through it. With case hardening, the depth of hardening is often enough to allow finish grinding in the hardened layer.
 
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