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Steel Making

The Influence Of Size
The size of the piece influences the physical properties obta...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

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

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

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

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

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

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

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

The Leeds And Northrup Potentiometer System
The potentiometer pyrometer system is both flexible and subst...

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

Sulphur is another impurity and high sulphur is even a greate...

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...

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

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

Phosphorus is one of the impurities in steel, and it has been...

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

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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