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Steel Making

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

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

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

Crankshaft
The crankshaft was the most highly stressed part of the entir...

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

Nickel-chromium
A combination of the characteristics of nickel and the charac...

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

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

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

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

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

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

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

Care In Annealing
Not only will benefits in machining be found by careful anne...

Refining The Grain
This is remedied by reheating the piece to a temperature slig...

The Electric Process
The fourth method of manufacturing steel is by the electric f...

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

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

Quenching
It is considered good practice to quench alloy steels from th...



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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