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Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

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

Phosphorus
Phosphorus is one of the impurities in steel, and it has been...

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

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

The Leeds And Northrup Potentiometer System
The potentiometer pyrometer system is both flexible and subst...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

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...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

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

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

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

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

High Speed Steel
For centuries the secret art of making tool steel was handed ...



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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