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

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

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

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

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

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

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

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

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

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

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

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

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

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

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

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...

Sulphur
Sulphur is another impurity and high sulphur is even a greate...



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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