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Steel Making

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

The Thermo-couple
With the application of the thermo-couple, the measurement of...

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

Sulphur
SULPHUR is another element (symbol S) which is always found i...

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

The Care Of Carburizing Compounds
Of all the opportunities for practicing economy in the heat-t...

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

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

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

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

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

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

Annealing
ANNEALING can be done by heating to temperatures ranging from...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...



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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