After quenching the knives I
take a metal file and try to file
the edge of the blade. If the
files skates across the surface
without digging in then the
steel got hard enough. If the
file cuts into the steel
something went wrong in the
heat treat stage and the knife
wont stay sharp.
In the picture notice the 4th
blade down..you can see the
hamon line is wavy and trails
off towards the tip...thats a big
no-no. The steel wasn't quite
hot enough when I quenched
and not all portions hardened,
so I must reheat treat it. (i'm
going to blame doing all the
photograhpy for the mistake
this time ;)
After steel is hardened it is too
hard and it will be brittle....so
what we now do is temper the
knives. For this application I
will be baking them in the oven
at 400 degrees for 3 cycles of
1 hour each. Before I stick the
blades in the oven I grind
some of the scale that formed
during heat treating off so i
can see plain steel. As steel is
heated it changes
colors...these colors form at
certain temps. At around 400
degrees a golden straw color
appears. i grind the scale off
the blade a bit so i can see the
golden hue form....that way i
know the right temp was
reached. Picture 1 shows the
knives before tempering,
picture 2 shows them
after...can you see the golden
tone that formed? All of the
blades turned this color, its
just not noticeable in this pic.
