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Steel Making

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

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

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...

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

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

High Speed Steel
For centuries the secret art of making tool steel was handed ...

Heat-treating Equipment And Methods For Mass Production
The heat-treating department of the Brown-Lipe-Chapin Company...

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...

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

This steel like any other steel when distorted by cold worki...

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

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

Highly Stressed Parts
The highly stressed parts on the Liberty engine consisted of ...

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

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

Nickel may be considered as the toughest among the non-rare a...

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

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

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

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

Temperatures To Use


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.

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
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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