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Steel Making

The Forging Of Steel
So much depends upon the forging of steel that this operation...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Heat-treating Equipment And Methods For Mass Production
The heat-treating department of the Brown-Lipe-Chapin Company...

Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

Phosphorus
Phosphorus is one of the impurities in steel, and it has been...

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

Chromium
Chromium when alloyed with steel, has the characteristic func...

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

Critical Points
One of the most important means of investigating the properti...

Hardness Testing
The word hardness is used to express various properties of me...



Steel For Chisels And Punches






Category: HARDENING CARBON STEEL FOR TOOLS

The highest grades of carbon or tempering steels are to be recommended
for tools which have to withstand shocks, such as for cold chisels
or punches. These steels are, however, particularly useful where
it is necessary to cut tempered or heat-treated steel which is
more than ordinarily hard, for cutting chilled iron, etc. They are
useful for boring, for rifle-barrel drilling, for fine finishing
cuts, for drawing dies for brass and copper, for blanking dies for
hard materials, for formed cutters on automatic screw machines
and for roll-turning tools.

Steel of this kind, being very dense in structure, should be given
more time in heating for forging and for hardening, than carbon
steels of a lower grade. For forging it should be heated slowly
and uniformly to a bright red and only light blows used as the
heat dies out. Do not hammer at all at a black heat. Reheat slowly
to a dark red for hardening and quench in warm water. Grind on a
wet grindstone.

Where tools have to withstand shocks and vibration, as in pneumatic
hammer work, in severe punching duty, hot or cold upsetting or
similar work, tool steels containing vanadium or chrome-vanadium
give excellent results. These are made particularly for work of
this kind.

CHISELS-SHAPES AND HEAT TREATMENT[1]


In the chief mechanical engineer's department of the Midland Ry.,
after considerable experimenting, it was decided to order chisel
steel to the following specifications: carbon, 0.75 to 0.85 per
cent, the other constituents being normal. This gives a complete
analysis as follows: carbon, 0.75 to 0.85; manganese, 0.30; silicon,
0.10; sulphur, 0.025; phosphorus, 0.025.

The analysis of a chisel which had given excellent service was as
follows: carbon, 0.75; manganese, 0.38; silicon, 0.16; sulphur,
0.028; phosphorus, 0.026. The heat treatment is unknown.


At the same time that chisel steel was standardized, the form of
the chisels themselves was revised, and a standard chart of these
as used in the locomotive shops was drawn up. Figure 83 shows the
most important forms, which are made to stock orders in the smithy
and forwarded to the heat-treatment room where the hardening and
tempering is carried out on batches of fifty. A standard system
of treatment is employed, which to a very large extent does away
with the personal element. Since the chemical composition is more
or less constant, the chief variant is the section which causes
the temperatures to be varied slightly. The chisels are carefully
heated in a gas-fired furnace to a temperature of from 730 to 740 deg.C.
(1,340 to 1,364 deg.F.) according to section. In practice, the first
chisel, is heated to 730 deg.C.; and the second to 735 deg.C. (1,355 deg.F.);
and a 1 in. half round chisel to 740 deg.C., because of their varying
increasing thickness of section at the points. Upon attaining this
steady temperature, the chisels are quenched to a depth of 3/8
to 1/2 in. from the point in water, and then the whole chisel is
immersed and cooled off in a tank containing linseed oil.

The oil-tank is cooled by being immersed in a cold-water tank through
which water is constantly circulated. After this treatment, the
chisels have a dead hard point and a tough or sorbitic shaft. They
are then tempered or the point let down. This is done by immersing
them in another oil-bath which has been raised to about 215 deg.C.
(419 deg.F). The first result is, of course, to drop the temperature
of the oil, which is gradually raised to its initial point. On
approaching this temperature the chisels are taken out about every
2 deg.C. rise and tested with a file, and at a point between 215 and
220 deg.C. (428 deg.F.), when it is found that the desired temper has been
reached, the chisels are removed, cleaned in sawdust, and allowed
to cool in an iron tray.

No comparative tests of these chisels with those bought and treated
by the old rule-of-thumb methods have been made, as no exact method of
carrying out such tests mechanically, other than trying the hardness
by the Brinell or scleroscope method, are known; any ordinary test
depends so largely upon the dexterity of the operator. The universal
opinion of foremen and those using the chisels as to the advantages
of the ones receiving the standard treatment described is that
a substantial improvement has been made. The chisels were not
normalized. Tests of chisels normalized at about 900 deg.C. (1,652 deg.F.)
showed that they possessed no advantage.

Tools or pieces which have holes or deep depressions should be
filled before heating unless it is necessary to have the holes
hard on the inside. In that case the filling would keep the water
away from the surface and no hardening would take place. Where
filling is to be done, various materials are used by different
hardeners. Fireclay and common putty seem to be favored by many.

Every mechanic who has had anything to do with the hardening of
tools knows how necessary it is to take a cut from the surface of
the bar that is to be hardened. The reason is that in the process
of making the steel its outer surface has become decarbonized.
This change makes it low-carbon steel, which will of course not
harden. It is necessary to remove from 1/16 to 1/4 in. of diameter
on bars ranging from 1/2 to 4 in.

This same decarbonization occurs if the steel is placed in the
forge in such a way that unburned oxygen from the blast can get at
it. The carbon is oxidized, or burned out, converting the outside
of the steel into low-carbon steel. The way to avoid this is to use
a deep fire. Lack of this precaution is the cause of much spoiled
work, not only because of decarbonization of the outer surface
of the metal, but because the cold blast striking the hot steel
acts like boiling hot water poured into an ice-cold glass tumbler.
The contraction sets up stresses that result in cracks when the
piece is quenched.





Next: Preventing Decarbonization Of Tool Steel

Previous: Uses Of The Various Tempers Of Carbon Tool Steel



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