Hardening High-speed Steels





We will now take up the matter of hardening high-speed steels. The

most ordinary tools used are for lathes and planers. The forging

should be done at carbon-steel heat. Rough-grind while still hot

and preheat to about carbon-steel hardening heat, then heat quickly

in high-speed furnace to white heat, and quench in oil. If a very

hard substance is to be cut, the point of tool may be quenched in

kerosene or water and when nearly black, finish cooling in oil.

Tempering must be done to suit the material to be cut. For cutting

cast iron, brass castings, or hard steel, tempering should be done

merely to take strains out of steel.



On ordinary machinery steel or nickel steel the temper can be drawn

to a dark blue or up to 900 deg.F. If the tool is of a special form

or character, the risk of melting or scaling the point cannot be

taken. In these cases the tool should be packed, but if there is

no packing equipment, a tool can be heated to as high heat as is

safe without risk to cutting edges, and cyanide or prussiate of

potash can be sprinkled over the face and then quenched in oil.



Some very adverse criticism may be heard on this point, but experience

has proved that such tools will stand up very nicely and be perfectly

free from scales or pipes. Where packing cannot be done, milling

cutters, and tools to be hardened all over, can be placed in muffled

furnace, brought to 2,220 deg. and quenched in oil. All such tools,

however, must be preheated slowly to 1,400 to 1,500 deg. then placed in

a high-speed furnace and brought up quickly. Do not soak high-speed

steel at high heats. Quench in oil.



We must bear in mind that the heating furnace is likely to expand

tools, therefore provision must be made to leave extra stock to

take care of such expansion. Tools with shanks such as counter

bores, taps, reamers, drills, etc., should be heated no further

than they are wanted hard, and quench in oil. If a forge is not

at hand and heating must be done, use a muffle furnace and cover

small shanks with a paste from fire clay or ground asbestos. Hollow

mills, spring threading dies, and large cutting tools with small

shanks should have the holes thoroughly packed or covered with

asbestos cement as far as they are wanted soft.





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