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

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Annealing Method
Forgings which are too hard to machine are put in pots with ...

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

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

Vanadium
Vanadium has a very marked effect upon alloy steels rich in c...

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

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

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...

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

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

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

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

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

Critical Points
One of the most important means of investigating the properti...

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...



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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