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

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

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

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

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

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

The Modern Hardening Room
A hardening room of today means a very different place from ...

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

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

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

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

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

Complete Calibration Of Pyrometers
For the complete calibration of a thermo-couple of unknown e...



Chromium






Category: ALLOYS AND THEIR EFFECT UPON STEEL

Chromium when alloyed with steel, has the characteristic function
of opposing the disintegration and reconstruction of cementite.
This is demonstrated by the changes in the critical ranges of this
alloy steel taking place slowly; in other words, it has a tendency
to raise the Ac range (decalescent points) and lower the Ar
range (recalescent points). Chromium steels are therefore capable
of great hardness, due to the rapid cooling being able to retard
the decomposition of the austenite.

The great hardness of chromium steels is also due to the formation
of double carbides of chromium and iron. This condition is not
removed when the steel is slightly tempered or drawn. This additional
hardness is also obtained without causing undue brittleness such as
would be obtained by any increase of carbon. The degree of hardness
of the lower-chrome steels is dependent upon the carbon content,
as chromium alone will not harden iron.

The toughness so noticeable in this steel is the result of the
fineness of structure; in this instance, the action is similar
to that of nickel, and the tensile strength and elastic limit is
therefore increased without any loss of ductility. We then have
the desirable condition of tough hardness, making chrome steels
extremely valuable for all purposes requiring great resistance
to wear, and in higher-chrome contents resistance to corrosion.
All chromium-alloy steels offer great resistance to corrosion and
erosion. In view of this, it is surprising that chromium steels
are not more largely used for structural steel work and for all
purposes where the steel has to withstand the corroding action
of air and liquids. Bridges, ships, steel building, etc., would
offer greater resistance to deterioration through rust if the
chromium-alloy steels were employed.

Prolonged heating and high temperatures have a very bad effect upon
chromium steels. In this respect they differ from nickel steels,
which are not so affected by prolonged heating, but chromium steels
will stand higher temperatures than nickel steels when the period
is short.

Chromium steels, due to their admirable property of increased hardness,
without the loss of ductility, make very excellent chisels and
impact tools of all types, although for die blocks they do not give
such good results as can be obtained from other alloy combinations.

For ball bearing steels, where intense hardness with great toughness
and ready recovery from temporary deflection is required, chromium
as an alloy offers the best solution.

Two per cent chromium steels; due to their very hard tough surface,
are largely used for armor-piercing projectiles, cold rolls, crushers,
drawing dies, etc.

The normal structure of chromium steels, with a very low carbon
content is roughly pearlitic up to 7 per cent, and martensitic
from 8 to 20 per cent; therefore, the greatest application is in
the pearlitic zone or the lower percentages.





Next: Nickel-chromium

Previous: Nickel



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