How much heat does it take to ruin temper?

[Phil Wilson]

p3pe, a couple more thoughts to add to your relief. If you heat one side of a blade the heat is being conducted away almost as fast on the other side. Depending on the original tempering temp you would have to see at least light straw color on both sides to have done any damage. Also tempering either on purpose or accidental is time related. if you get a blade too hot due to contact with a grinding belt or sharpening wheel you would instantly see some color change. If you got it say dark brown on both side of the edge then some damage is done but only in that area. Heating with hot air like you did would take some time to have any effect. In fact with most steels it takes at least an hour for the full temper effect. Phil

[hokie88]

It's be awhile since material science but I remember Austenite being the hardest and if you heat it you get like cementite and perlite and can't get back. The image is arbitrary its called a two-phase diagram you need to find one of those for the type of steel in question which is probably hard to find.

http://www.substech.com/dokuwiki/lib/ex ... iagram.png