Hardened tool steel has soft outside layer

spend a little more money and get some A-2 and wrap it tight. never fails me

Tom

When using a torch the thing to remember is that both acetylene or propane both contain carbon in there chemical composition and therefore will stop any decarb or oxidization when the flame is set correctly. As to the decarb I should also really have mentioned oxidization, which would occur instantly when you remove it form the protective vacuum, I am assuming scale is forming on the work piece before it gets to the quench, also if the vacuum is not high enough this would be detrimental. The vacuum furnaces I work with go down to about 3 x 10 -4 and use nitrogen quench straight into the main chamber in conjunction with a circulating fan so I am not au fait with the concept of heating in a vacuum and then removing to quench in oil. My furnaces would go into self-destruct mode if I tried to open them at high temperatures. Pumps would explode and elements disintegrate, but I have treated more O1 in a salt bath than you can shake a stick at.

Ian

You do not say whether the tool steel you are trying to harden has been ground prior to heat-treatment. All the "black" carbon tool steels have a layer of about the dimensions you quote that has lost carbon during manufacture. It has to be machined away prior to ht if you are to achieve full hardness at the surface.

Bob

This is probably a decarbonization problem, the carbon in the outer layer is oxidized therefore the alloy in the outer layer is no longer a high carbon alloy. You need to use an inert gas atmosphere or a carbon rich atmosphere.

I am saying that it is useful to check assumptions that are checkable.

Michael Dahms

BTW: Please do not full-quote and top-post any more!

How do I check the carbon level in the outer layer?

BTW - my assumption is based on several sources of reference materials which suggest that vacuum ovens do not deplete the carbon levels.

You should look to the microstructure at first. Maybe, you can show us a picture. A decarburized zone can be seen as ferritic surface layer.

Michael Dahms