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Steel Making

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

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

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

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

Furnace Data
In order to give definite information concerning furnaces, fu...

Conclusions
Martien was probably never a serious contender for the honor ...

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

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

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

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

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...

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

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

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

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

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...



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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