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Steel Making

Annealing
ANNEALING can be done by heating to temperatures ranging from...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

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

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

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

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

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

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

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

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

Furnace Data
In order to give definite information concerning furnaces, fu...

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

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

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...



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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