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Steel Making

Manganese
Manganese adds considerably to the tensile strength of steel,...

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

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

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

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

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

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

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

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

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

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

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

Air-hardening Steels
These steels are recommended for boring, turning and planing...

Knowing What Takes Place
How are we to know if we have given a piece of steel the ver...

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

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...



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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