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Steel Making

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

Hardness Testing
The word hardness is used to express various properties of me...

Take Time For Hardening
Uneven heating and poor quenching has caused loss of many ve...

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

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

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

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

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

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

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

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

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

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

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

Chromium
Chromium when alloyed with steel, has the characteristic func...

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

Standard Analysis
The selection of a standard analysis by the manufacturer is t...

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...



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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