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Steel Making

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

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

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

Impact Tests
Impact tests are of considerable importance as an indication ...

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

Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

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

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

Heating
Although it is possible to work steels cold, to an extent de...

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...

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

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

Effects Of Proper Annealing
Proper annealing of low-carbon steels causes a complete solu...

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

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

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

Gears
The material used for all gears on the Liberty engine was sel...



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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