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Steel Making

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

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

Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...

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

Phosphorus
Phosphorus is one of the impurities in steel, and it has been...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

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

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

Effect Of Different Carburizing Material
[Illustrations: FIGS. 33 to 37.] Each of these different p...

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

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

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

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

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

Highly Stressed Parts
The highly stressed parts on the Liberty engine consisted of ...

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

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...



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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