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Steel Making

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

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

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

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

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

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

Judging The Heat Of Steel
While the use of a pyrometer is of course the only way to hav...

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

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

Tungsten
Tungsten, as an alloy in steel, has been known and used for a...

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

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

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

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



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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