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

substances.





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