OIL
I normally use 5-weight oil for all my quenching, but any mineral oil 5 weight or less will work fine. The
temperature of the oil should be held 100 to 130 degrees F.
LYE
Carbon Steels may be quenched in a 5% lye solution with very good results. I have found that it will
eliminate soft spots in the steel. It will give a bright finish; in addition, it will not rust the tools if they are
not dipped in oil.
TEMPERING
Now comes the most important part of heat-treating process and that is of tempering of the metal.
Harden steel can be tempered or made softer and less brittle by re-heating it to a predetermined
temperature. Depending upon the nature of the steel and its intended use, and then the cooling.
When the tempering is done by the color method, the temper is gauged by the colors formed on the
surface of the polished metal as the heat increases. The color method of gauging temperatures is not
dependable, as the color is affected, to some extent, by the composition of the metal. Tempilaq is a
compound that you can buy, in any temperature range, to put on the metal.
When it melts you, have the metal at the proper temperature. It is better to have a temperature gauge to
get the correct temperature. After you have worked with a certain type of steel for a while, you will be
able to judge the correct temperature by the color. It is best to polish the metal to a bright finish so the
color can be seen clearly.
COLORS FOR TEMPERING
430 degrees, Very pale yellow, extra file hard, dies, milling cutters, cut off tools.
440 degrees, Light Yellow, file hard, reamers, thread chasers; fly cutters, and hollow mills.
450 degrees, Pale straw yellow, profile cutters for milling machines, rolling dies, knurling tools.
460 degrees, Straw yellow, knife hard, swages.
470 degrees, deep straw yellow.
480 degrees, Dark yellow, cutting dies.