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Annealing Work
With the exception of several of the higher types of alloy s...

Care In Annealing
Not only will benefits in machining be found by careful anne...

Manganese
Manganese adds considerably to the tensile strength of steel,...

Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

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

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

Hardness Testing
The word hardness is used to express various properties of me...

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

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

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

Pickling The Forgings
The forgings were then pickled in a hot solution of either ni...

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....

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

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

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

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

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

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

Chromium
Chromium when alloyed with steel, has the characteristic func...

The Influence Of Size
The size of the piece influences the physical properties obta...



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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