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Drop Forging Dies
The kind of steel used in the die of course influences the he...

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...

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

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

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

Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

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

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

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

Hardening
The forgings can be hardened by cooling in still air or quen...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

Vanadium
Vanadium has a very marked effect upon alloy steels rich in c...

Conclusions
Martien was probably never a serious contender for the honor ...

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

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

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

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

The Thermo-couple
With the application of the thermo-couple, the measurement of...



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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