Question for knife makers

[thboz]

My question is regarding the tempering of an knife blade. I should say re-tempering. I left it in the oven a little long or the thermostat was off a little. I set it at 450 degrees. It got into the purple range. I would like to know if I can just temper again, or do I have to heat treat again? The knife is made from a file. Tom

 

[jaguarxk120]

I would think that the tempering process takes out the hardness from the steel and makes it tougher. Have you tried it at the temper it's at now? If too soft then reharding is in order. You might want to look around for a infrared therometer to check oven temps. Good luck TF

 

[LRB]

If you want it harder, you will have to re-harden. Buy an oven thermometer, they are not over $5.oo. Never trust the settings on your range, especially gas ranges. For max temper, give it three one hour tempers, letting it cool to room temp in between.

 

[rich pierce]

Purple may work. Old butcher knives were not quite as hard as new custom knives are made now. Files are very high carbon. Try it with a fine needle file, then try the edge of a dull kitchen knife and a dull pocket knife with the same file.

The purpose of the knife will also dictate how hard you want it to be as opposed to tough. If you will use it roughly, you'll want it a bit softer. Cleavers are not made as hard as boning knives.

 

[thboz]

Thank's for the replies. I think I will live with it as is. I tried a needle file on a carbon steel paring knife ( old one ) I have and the knife I'm making from file. The new one is quite a bit harder. I think I'll put the handle on it and move on to my next one. (from cut off saw blade ) Thanks again. Tom