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Steel Making

The Modern Hardening Room
A hardening room of today means a very different place from ...

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

Hardness Testing
The word hardness is used to express various properties of me...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

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

Drop Forging Dies
The kind of steel used in the die of course influences the he...

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

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

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Steel is hardened by quenching from above the upper critical....

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

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

ANNEALING can be done by heating to temperatures ranging from...

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

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

There is no mystery or secret about the proper annealing of d...

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

Carburizing Material


The simplest carburizing substance is charcoal. It is also the
slowest, but is often used mixed with something that will evolve
large volumes of carbon monoxide or hydrocarbon gas on being heated.
A great variety of materials is used, a few of them being charcoal
(both wood and bone), charred leather, crushed bone, horn, mixtures
of charcoal and barium carbonate, coke and heavy oils, coke treated
with alkaline carbonates, peat, charcoal mixed with common salt,
saltpeter, resin, flour, potassium bichromate, vegetable fibre,
limestone, various seed husks, etc. In general, it is well to avoid
complex mixtures.

H. L. Heathcote, on analyzing seventeen different carburizers, found
that they contained the following ingredients:

Per cent
Moisture 2.68 to 26.17
Oil 0.17 to 20.76
Carbon (organic) 6.70 to 54.19
Calcium phosphate 0.32 to 74.75
Calcium carbonate 1.20 to 11.57
Barium carbonate nil to 42.00
Zinc oxide nil to 14.50
Silica nil to 8.14
Sulphates (SO3) trace to 3.45
Sodium chloride nil to 7.88
Sodium carbonate nil to 40.00
Sulphides (S) nil to 2.80

Carburizing mixtures, though bought by weight, are used by volume,
and the weight per cubic foot is a big factor in making a selection.
A good mixture should be porous, so that the evolved gases, which
should be generated at the proper temperature, may move freely
around the steel objects being carburized; should be a good conductor
of heat; should possess minimum shrinkage when used; and should
be capable of being tamped down.

Many secret mixtures are sold, falsely claimed to be able to
convert inferior metal into crucible tool steel grade. They are
generally nothing more than mixtures of carbonaceous and cyanogen
compounds possessing the well-known carburizing properties of those

Next: Quenching

Previous: Rate Of Absorption

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