Hardening High-speed Steel
Category: HIGH-SPEED STEEL
In forging use coke for fuel in the forge. Heat steel slowly and
thoroughly to a lemon heat. Do not forge at a lower heat. Do not
let the steel cool below a bright cherry red while forging. After
the tool is dressed, reheat to forging heat to remove the forging
strain, and lay on the floor until cold. Then have the tool rough
ground on a dry emery wheel.
dotted line. Remember this is a boring mill tool and will stand
out in the tool-post, and if you do not have a high thorough lemon
heat, your tool will snap off at the dotted line. (Ninety-five
per cent of all tools which break, have been forged at too low a
heat or at a heat not thorough to the center.)]
For built-up and bent tools special care should be taken that the
forging heat does not go below a bright cherry. For tools 3/4 by
1-1/2 or larger where there is a big strain in forging, such as
bending at angles of about 45 deg. and building the tools up, they
should be heated to at least 1,700 deg.F. Slowly and without much blast.
For a 3/4 by 1-1/2 tool it should take about 10 min. with the correct
blast in a coke fire. Larger tools in proportion. They can then be
bent readily, but no attempt should be made to forge the steel
further without reheating to maintain the bright cherry red. This
is essential, as otherwise the tools crack in hardening or while
In hardening place the tool in a coke fire (hollow fire if possible)
with a slow blast and heat gradually up to a white welding heat
on the nose of the tool. Then dip the white hot part only into
thin oil or hold in a strong cold air blast. When hardening in
oil do not hold the tool in one place but keep it moving so that
it cools as quickly as possible. It is not necessary to draw the
temper after hardening these tools.
In grinding all tools should be ground as lightly as possible on
a soft wet sandstone or on a wet emery wheel, and care should be
taken not to create any surface cracks, which are invariably the
result of grinding too forcibly. The foregoing illustrations, Figs.
84 to 91, with their captions, will be found helpful.
Special points of caution to be observed when hardening high-speed
DON'T use a green coal fire; use coke, or build a hollow fire.
DON'T have the bed of the fire free from coal.
DON'T hurry the heating for forging. The heating has to be done
very slowly and the forging heat has to be kept very high (a full
lemon color) heat and the tool has to be continually brought back
into the fire to keep the high heat up. When customers complain
about seams and cracks, in 9 cases out of 10, this has been caused
by too low a forging heat, and when the blacksmith complains about
tools cracking, it is necessary to read this paragraph to him.
DON'T try to jam the tool into shape under a steam hammer with one
or two blows; take easy blows and keep the heat high.
DON'T have the tool curved at the bottom; it must lie perfectly
flat in the tool post.
DON'T harden from your forging heat; let the tool grow cold or
fairly cold. After forging you can rough grind the tool dry, but
not too forcibly.
DON'T, for hardening, get more than the nose white hot.
DON'T get the white heat on the surface only.
DON'T hurry your heating for hardening; let the heat soak thoroughly
through the nose of the tool.
DON'T melt the nose of the tool.
DON'T, as a rule, dip the nose into water; this should be done
only for extremely hard material. It is dangerous to put the nose
into water for fear of cracking and when you do put the nose into
water put just 1/2 in. only of the extreme white hot part into the
water and don't keep it too long in the water; just a few seconds,
and then harden in oil. We do not recommend water hardening.
DON'T grind too forcibly.
DON'T grind dry after hardening.
DON'T discolor the steel in grinding.
DON'T give too much clearance on tools for cutting cast iron.
DON'T start on cast iron with a razor edge on the tool. Take an
oil stone and wipe three or four times over the razor edge.
DON'T use tool holder steel from bars without hardening the nose
of each individual tool bit.
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