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

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

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

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

Quenching
It is considered good practice to quench alloy steels from th...

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

Compensating Leads
By the use of compensating leads, formed of the same materia...

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

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

Connecting Rods
The material used for all connecting rods on the Liberty engi...

Knowing What Takes Place
How are we to know if we have given a piece of steel the ver...

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

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

Silicon
SILICON is a very widespread element (symbol Si), being an es...

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

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

Nickel
Nickel may be considered as the toughest among the non-rare a...

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



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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