Cooling.—We recommend quenching all of the above tools in oil when taken from the fire. We have found fish oil, cottonseed oil, Houghton's No. 2 soluble oil and linseed oil satisfactory. The high heat is the important thing in hardening Blue Chip tools. If a white hot tool is allowed to cool in the open air it will be hard, but the air scales the tool.
Drawing the Temper.—Tools of this class should be drawn considerably more than water-hardening steel for the same purpose.
HEAT TREATMENT OF PUNCHES AND DIES, SHEARS, TAPS, ETC.
Heating.—The degree to which tools of the above classes should be heated depends upon the shape, size and use for which they are intended. Generally, they should not be heated to quite as high a heat as lathe tools or milling cutters. They should have a high heat, but not enough to make the flux run on the steel (by pyrometer 1,900 to 2,100°F.).
Cooling.—Depending on the tools, some should be dipped in oil all over, some only part way, and others allowed to cool down in the air naturally, or under air blast. In cooling, the toughness is retained by allowing some parts to cool slowly and quenching parts that should be hard.
Drawing the Temper.—As in cooling, some parts of these tools will require more drawing than others, but, on the whole, they must be drawn more than water hardening tools for the same purpose or to about 500°F. all over, so that a good file will just "touch" the cutting or working parts.
Barium Chloride Process.—This is a process developed for treating certain classes of tools, such as taps, forming tools, etc. It is being successfully used in many large plants. Briefly the treatment is as follows:
In this treatment the tools are first preheated to a red heat, but small tools may be immersed without preheating. The barium chloride bath is kept at a temperature of from 2,000 to 2,100°F., and tools are held in it long enough to reach the same temperature. They are then dipped in oil. The barium chloride which adheres to the tools is brushed off, leaving the tools as dean as before heating.
A CHROMIUM-COBALT STEEL
The Latrobe Steel Company make a high-speed steel without tungsten, its red-hardness properties depending on chromium and cobalt instead of tungsten. It is known as P. R. K-33 steel. It does not require the high temperature of the tungsten steels, hardening at 1,830 to 1,850°F. instead of 2,200° or even higher, as with the tungsten.