"Tom Quackenbush" wrote in message
...

I'm wondering how this would affect "selective" (I don't know the
right word) tempering - as in applying a torch to the spine of a knife
blade in order to produce a hardness gradient from the spine to the
edge. Does this work at all, or is it counter-productive? Does it work
better with "forgiving" type steels (say, O-1 or simple carbon
steels)? Given the specific application of scarifying blades for a box
scraper, would I be better off wear facing the blades rather than
relying on tempering to achieve a hard face and softer, springy back?
Tom Q.

Tom,

There's a slightly better way of selective tempering and a few little tricks
you can use, most important is to do a full temper first to the correct heat
for the RC that you want the edge to be. Once this is done, there's a few
ways of producing a selective temper, the simplest and not requiring
technical know-how is to preheat a reasonable sized piece of steel, big
enough to lay the spine on and not so small that it loses it's heat too
quickly. Take it out and lay the spine of the edge tool on the hot metal and
watch till the straw colour approaches the blade edge (a good way to lose a
hamon though :-( ....) . Heat protecting gels just applied to the edge can
also help. it's a lot more controllable than the method you described with
direct torch heat. The other method is to build a small toaster device that
only the back of the blade sits in, only worth doing if you are planning on
doing lots of selective tempering.
got a link to a knife manufacturer's FAQ that uses selective tempering on
their blades, you might find it interesting.:
http://www.mdk.idv.tw/mdkfaq.htm#3.11

Simon