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Pyrometers
Armor plate makers sometimes use the copper ball or Siemens' ...

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

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

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

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

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

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

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

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

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

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

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

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

Effect Of Different Carburizing Material
[Illustrations: FIGS. 33 to 37.] Each of these different p...

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

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

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



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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