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Steel Making

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

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

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

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

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

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

Refining The Grain
This is remedied by reheating the piece to a temperature slig...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

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

Take Time For Hardening
Uneven heating and poor quenching has caused loss of many ve...

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Double Annealing
Water annealing consists in heating the piece, allowing it to...

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

Sulphur
Sulphur is another impurity and high sulphur is even a greate...

Corrosion
This steel like any other steel when distorted by cold worki...

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

The Thermo-couple
With the application of the thermo-couple, the measurement of...

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...



Nickel






Category: ALLOYS AND THEIR EFFECT UPON STEEL

Nickel may be considered as the toughest among the non-rare alloys
now used in steel manufacture. Originally nickel was added to give
increased strength and toughness over that obtained with the ordinary
rolled structural steel and little attempt was made to utilize its
great possibilities so far as heat treatment was concerned.

The difficulties experienced have been a tendency towards laminated
structure during manufacture and great liability to seam, both
arising from improper melting practice. When extra care is exercised
in the manufacture, particularly in the melting and rolling, many
of these difficulties can be overcome.

The electric steel furnace, of modern construction, is a very important
step forward in the melting of nickel steel; neither the crucible
process nor basic or acid open-hearth furnaces give such good results.

Great care must be exercised in reheating the billet for rolling
so that the steel is correctly soaked. The rolling must not be
forced; too big reduction per pass should not be indulged in, as
this sets up a tendency towards seams.

Nickel steel has remarkably good mechanical qualities when suitably
heat-treated, and it is preeminently adapted for case-hardening. It
is not difficult to machine low-nickel steel, consequently it is
in great favor where easy machining properties are of importance.

Nickel influences the strength and ductility of steel by being
dissolved directly in the iron or ferrite; in this respect differing
from chromium, tungsten and vanadium. The addition of each 1 per
cent nickel up to 5 per cent will cause an approximate increase of
from 4,000 to 6,000 lb. per square inch in the tensile strength and
elastic limit over the corresponding steel and without any decrease
in ductility. The static strength of nickel steel is affected to
some degree by the percentage of carbon; for instance, steel with
0.25 per cent carbon and 3.5 per cent nickel has a tensile strength,
in its normal state, equal to a straight carbon steel of 0.5 per
cent with a proportionately greater elastic limit and retaining
all the advantages of the ductility of the lower carbon.

To bring out the full qualities of nickel it must be heat-treated,
otherwise there is no object in using nickel as an alloy with carbon
steel as the additional cost is not justified by increased strength.

Nickel has a peculiar effect upon the critical ranges of steel,
the critical range being lowered by the percentage of nickel; in
this respect it is similar to manganese.

Nickel can be alloyed with steel in various percentages, each percentage
having a very definite effect on the microstructure. For instance, a
steel with 0.2 per cent carbon and 2 per cent nickel has a pearlitic
structure but the grain is much finer than if the straight carbon
were used. With the same carbon content and say 5 per cent nickel,
the structure would still be pearlitic, but much finer and denser,
therefore capable of withstanding shock, and having greater dynamic
strength. With about 0.2 per cent carbon and 8 per cent nickel, the
steel is nearing the stage between pearlite and martensite, and
the structure is extremely fine, the ferrite and pearlite having
a very pronounced tendency to mimic a purely martensite structure.
Steel with 0.2 per cent carbon and 15 per cent nickel is entirely
martensite. Higher percentages of nickel change the martensitic
structure to austenite, the steel then being non-magnetic. The
higher percentages, that is 30 to 35 per cent nickel, are used
for valve seats, valve heads, and valve stems, as the alloy is a
poor conductor of heat and is particularly free from any tendency
towards corrosion or pitting from the action of waste gases of
the internal-combustion engine.

Nickel steels having 3-1/2 per cent nickel and 0.15 to 0.20 per
cent carbon are excellent for case-hardening purposes, giving hard
surfaces and tough interiors.

To obtain the full effect of nickel as an alloy, it is essential
that the correct percentage of carbon be used. High nickel and
low carbon will not be more efficient than lower nickel and higher
carbon, but the cost will be much greater. Generally speaking,
heat-treated nickel alloy steels are about two to three times stronger
than the same steel annealed. This point is very important as many
instances have been found where nickel steel is incorrectly used,
being employed when in the annealed or normal state.





Next: Chromium

Previous: Hardness Testing



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