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Steel Making

Properties Of Alloy Steels
The following table shows the percentages of carbon, manganes...

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

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

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

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

Annealing Work
With the exception of several of the higher types of alloy s...

The Electric Process
The fourth method of manufacturing steel is by the electric f...

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

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

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

Air-hardening Steels
These steels are recommended for boring, turning and planing...

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

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

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

Connecting Rods
The material used for all connecting rods on the Liberty engi...

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

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

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

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



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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