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 deg.F. instead of 2,200 deg. or even higher, as with the tungsten.



This steel is forged at 1,900 to 2,000 deg.F. and must not be worked

at a lower temperature than 1,600 deg.F. It requires soaking in the

fire more than the tungsten steels. It can be normalized by heating

slowly and thoroughly to 1,475 deg.F., holding this for from 10 to 20

min. according to the size of the piece and cooling in the open

air, protected from drafts.



A peculiarity of this steel is that it becomes non-magnetic at or

above 1,960 deg.F. and the magnetic quality is not restored by cooling.

Normalizing as above, however, restores the magnetic qualities. This

enables the user to detect any tools which have been overheated,

with a horseshoe magnet.



It is sometimes advantageous to dip tools, before heating for hardening,

in ordinary fuel or quenching oil. The oil leaves a thin film of

carbon which tends to prevent decarbonization, giving a very hard

surface.



For other makes of high-speed steel used in lathe and planer tools

the makers recommend that the tools be cut from the bar with a

hack saw or else heated and cut with a chisel. The heating should

be very slow until the steel reaches a red after which it can be

heated more rapidly and should only be forged at a high heat. It

can be forged at very high heats but care should be taken not to

forge at a low heat. The heating should be uniform and penetrate

clear to the center of the bar before forging is begun. Reheat

as often as necessary to forge at the proper heat.



After forging cool in lime before attempting to harden. Do not

attempt to harden with the forging heat as was sometimes done with

the carbon tools.



For hardening forged tools, heat slowly up to a bright red and

then rapidly until the point of the tool is almost at a melting

heat. Cool in a blast of cold, dry air. For large sizes of steel,

cool in linseed oil or in fish oil as is most convenient. If the

tools are to be used for finishing cuts heat to a bright yellow

and quench in oil. Grind for use on a sand wheel or grindstone

in preference to an emery or an artificial abrasive wheel.



For hardening milling and similar cutters, preheat to a bright

red, place the cutter on a round bar of suitable size, and revolve

it quickly over a very hot fire. Heat as high as possible without

melting the points of the teeth and cool in a cold blast of dry

air or in fish oil.



Light fragile cutters, twist drills, taps and formed cutters may

be heated almost white and then dipped in fish oil for hardening.

Where possible it is better to give an even higher heat and cool

in the blast of cold, dry air as previously recommended.





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