What is differential hardening?

[golok]

I have come across this term now and then. I take it to mean that different parts of a single blade are subjected to varying temperatures in the hardening process.

Am I right? Or, is tbere a simpler and more accurate explanation?

 

[kile]

The most basic form of differential hardening is to heat the whole blade to critical temperature, but only quench the edge of the blade, this leaves a hard cutting edge, but a softer back which in theory adds toughness to the whole blade. There are other ways to acheive the same result, such as only heating the edge past critical and quenching the whole blade, or using clay to cover the back of the blade so it doesn't cool as quickly. There is also diffential tempering which involves hardening the whole blade, and then tempering the spine of the blade at a higher temperature than the cutting edge.
Most of the time these teqhniques are only used on carbon steels, although occasionally people have differentially harderend stainless steels as well.
Kyle Fuglesten