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

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

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

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

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

Placing Of Pyrometers
When installing a pyrometer, care should be taken that it re...

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

Quenching The Work
In some operations case-hardened work is quenched from the bo...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

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

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

Machineability
Reheating for machine ability was done at 100 deg. less than ...

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

Quality And Structure
The quality of high-speed steel is dependent to a very great ...

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

Carbon-steel Forgings
Low-stressed, carbon-steel forgings include such parts as car...

Bessemer Process
The bessemer process consists of charging molten pig iron int...

Conclusions
Martien was probably never a serious contender for the honor ...



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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