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Compensating Leads
By the use of compensating leads, formed of the same materia...

Crucible Steel
Crucible steel is still made by melting material in a clay or...

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

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

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

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

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

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

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

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

Double Annealing
Water annealing consists in heating the piece, allowing it to...

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

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

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

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

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

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

Placing Of Pyrometers
When installing a pyrometer, care should be taken that it re...



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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