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Making Steel Balls
Steel balls are made from rods or coils according to size, st...

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

Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

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

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

The Effect Of Tempering On Water-quenched Gages
The following information has been supplied by Automatic and ...

Silicon
SILICON is a very widespread element (symbol Si), being an es...

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

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...

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

The Modern Hardening Room
A hardening room of today means a very different place from ...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

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

Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

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

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

Manganese
MANGANESE is a metal much like iron. Its chemical symbol is M...



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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