Thread: Heat-Treating Basics

WOW! Josh
Just getting into tempering knife blades and you really gave me some great info on temps.
Thanks!

Really like your post and loved your razors.

Thanks,

McKie

Very informative, can't wait for the next chapter!

In general terms this post is very well done and should be left as is for reference and basic understanding of the meat treating process. Since we reference a long lasting edge to hardness I would like to mention that in a typical furnace the metal being heat treated looses some carbon to the air creating co2 which results in a lower hardness in the end result. To reduce the loss of carbon to the atmosphere furnaces have an atmosphere control. I believe they flood the furnace chamber with nitrogen but it may be some other inert gas that is used. These furnaces are more expensive and typically not in smaller machine shops that do their own heat treating. To avoid the carbon loss the items being heat threated are put in a metal foil pouch that is sealed by folding the edges over several times. This limits the amount of oxygen available to form co2 and limits the carbon loss in the metal. By limiting the amount of carbon loss the hrc of the metal after tempering will be higher under the same tempering conditions.

foil wrap is not used for the most part on oil quench or water quench steels
most makers i know leave a bit of extra thickness on the blade before heat treat and then grind clean
alot of production knife makers grind there blanks full hard and not even part ground before heat treat (shaped yes but not beveled )


for the more simple steels 10xx and the like the quench from temp is only around 1500 ish and soak times are short so decarb may not be a big deal

not like when i do SS at 2050f for a 30 min soak. with out foil there would be nothing left of the blade to use

Originally Posted by Joed

To reduce the loss of carbon to the atmosphere furnaces have an atmosphere control. I believe they flood the furnace chamber with nitrogen but it may be some other inert gas that is used. These furnaces are more expensive and typically not in smaller machine shops that do their own heat treating. To avoid the carbon loss the items being heat threated are put in a metal foil pouch that is sealed by folding the edges over several times.

The gas is argon. It is actually available in small kilns too. Flooding of the chamber tends to ruin the elements quickly and most manufacturers warn against this. I've known knifemakers who have tried HT with and without the argon flood... Without works better. Butch is right that the foil is only really used on Stainless.

So, when quenching, if you were to use something really cold, it would trap more of the carbon, right? Leaving you with a harder steel?

That is logical thinking but it is the wrong thing to do. Think in terms of thermal shock. If you take a high carbon steel and quench it in cold water then it will most likely crack the blade or warp it.
Generally speaking I have the quench at 100 degrees or better for 1095 steel.

You will learn, as I did, the hard way!