Annealing Of High-speed Steel





For annealing high-speed steel, some makers recommend using ground

mica, charcoal, lime, fine dry ashes or lake sand as a packing

in the annealing boxes. Mixtures of one part charcoal, one part

lime and three parts of sand are also suggested, or two parts of

ashes may be substituted for the one part of lime.



To bring about the softest structure or machine ability of high-speed

steel, it should be packed in charcoal in boxes or pipes, carefully

sealed at all points, so that no gases will escape or air be admitted.

It should be heated slowly to not less than 1,450 deg.F. and the steel

must not be removed from its packing until it is cool. Slow heating

means that the high heat must have penetrated to the very core of

the steel.



When the steel is heated clear through it has been in the furnace

long enough. If the steel can remain in the furnace and cool down

with it, there will be no danger of air blasts or sudden or uneven

cooling. If not, remove the box and cover quickly with dry ashes,

sand or lime until it becomes cold.



Too high a heat or maintaining the heat for too long a period,

produces a harsh, coarse grain and greatly increases the liability

to crack in hardening. It also reduces the strength and toughness

of the steel.



Steel which is to be used for making tools with teeth, such as

taps, reamers and milling cutters, should not be annealed too much.

When the steel is too soft it is more apt to tear in cutting and

makes it more difficult to cut a smooth thread or other surface.

Moderate annealing is found best for tools of this kind.





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