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Steel Making

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

Drop Forging Dies
The kind of steel used in the die of course influences the he...

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

Quenching
It is considered good practice to quench alloy steels from th...

Impact Tests
Impact tests are of considerable importance as an indication ...

Crucible Steel
Crucible steel is still made by melting material in a clay or...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

Judging The Heat Of Steel
While the use of a pyrometer is of course the only way to hav...

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

Manganese
Manganese adds considerably to the tensile strength of steel,...

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...



Temperatures To Use






Category: HARDENING CARBON STEEL FOR TOOLS

As soon as the temperature of the steel reaches
100 deg.C. (212 deg.F.) the transformation begins, increasing in intensity
as the temperature is raised, until finally when the lower critical
range is reached, the steel has been all changed into the ordinary
constituents of unhardened steels.

If a piece of polished steel is heated in an ordinary furnace, a
thin film of oxides will form on its surface. The colors of this
film change with temperature, and so, in tempering, they are generally
used as an indication of the temperature of the steel. The steel
should have at least one polished face so that this film of oxides
may be seen.

An alternative method to the determination of temper by color is
to temper by heating in an oil or salt bath. Oil baths can be used
up to temperatures of 500 deg.F.; above this, fused-salt baths are
required. The article to be tempered is put into the bath, brought
up to and held at the required temperature for a certain length
of time, and then cooled, either rapidly or slowly. This takes
longer than the color method, but with low temperatures the results
are more satisfactory, because the temperature of the bath can
be controlled with a pyrometer. The tempering temperatures given
in the following table are taken from a handbook issued by the
Midvale Steel Company.

TABLE 23.--TEMPERING TEMPERATURES FOR STEELS
----------------------------------------------------------------------------
Temperature Temperature
for 1 hr. for 8 min.
--------------- Color --------------- Uses
Deg. F.Deg. C. Deg. F.Deg. C.
-----------------------------------------------------------------------
370 188 Faint yellow 460 238 Scrapers, brass-turning tools,
reamers, taps, milling cutters,
saw teeth.
390 199 Light straw 510 265 Twist drills, lathe tools,
planer tools, finishing tools
410 210 Dark straw 560 293 Stone tools, hammer faces,
chisels for hard work, boring
cutters.
430 221 Brown 610 321 Trephining tools, stamps.
450 232 Purple 640 337 Cold chisels for ordinary work,
carpenters' tools, picks, cold
punches, shear blades, slicing
tools, slotter tools.
490 254 Dark blue 660 343 Hot chisels, tools for hot
work, springs.
510 265 Light blue 710 376 Springs, screw drivers.
----------------------------------------------------------------------------

It will be noted that two sets of temperatures are shown, one being
specified for a time interval of 8 min. and the other for 1 hr. For
the finest work the longer time is preferable, while for ordinary
rough work 8 min. is sufficient, after the steel has reached the
specified temperature.

The rate of cooling after tempering seems to be immaterial, and
the piece can be cooled at any rate, providing that in large pieces
it is sufficiently slow to prevent strains.





Next: Knowing What Takes Place
Previous: The Theory Of Tempering



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