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Steel Making

Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

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

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

Manganese
MANGANESE is a metal much like iron. Its chemical symbol is M...

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

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

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

Pyrometers
Armor plate makers sometimes use the copper ball or Siemens' ...

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

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

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

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

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

Effects Of Proper Annealing
Proper annealing of low-carbon steels causes a complete solu...

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...

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

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

Quality And Structure
The quality of high-speed steel is dependent to a very great ...



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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