A practical manual of autogenous welding, (oxy-acetylene) with a chapter on the cutting of metals with the blowpipe by Granjon R

Author:Granjon, R
Language: eng
Format: epub, pdf
Tags: Welding
Publisher: London, Griffin
Published: 1915-03-25T05:00:00+00:00

tion of the oxide of the metal in fusion, may be considered as undergoing true combustion during the course of welding.

In each case impoverishment of the line of welding is produced by volatilisation or burning, and conseqiiently a change in the nature of the metal in relation to the rest of the article follows— this should be avoided.

According to the alloys, the welder can avoid this volatilisation or burning of the elements, or remedy it by using, for example, a welding rod containing an excess of the element which tends to disappear and thus replace it by an equal portion.

CARBONISATION—DECARBONISATION.

The steels and cast iron are alloys of iron and carbon, the proportion of the latter element being 0*05 per cent, (extra mild steel), 1*5 per cent, (extra hard steel), and can attain 4'5 to 5 per cent, in the cast irons.

The carbon can burn either directly by contact with oxygen or by the reduction of the oxide of iron ; in each case there is a decar-bonisation of the metal, and the phenomenon is similar to that just studied in the preceding paragraph.

There can also take place carbonisation of irons and steels, that is to say, addition of carbon to the metal, since carbon tends to be taken up. In fact, if the flame contains an excess of acetylene, the carbon content can be added to, that is to say, it will unite with the iron at the high temperature. This is so true that one can carbonise mild steel with the aid of an oxy-acetylene flame containing an excess of acetylene.

The welder should remember these phenomena of carbonisation and decarbonisation in all cases where he is working with the blowpipe on iron or its alloys.

SEGREGATION: SEPARATION OF THE ELEMENTS.

When certain alloys are raised, under special conditions, to a definite temperature, the phenomenon known as segregation or liquation occurs in which the elements separate one from the other.

This property, which has to be carefully considered in the manufacture of welding rods because the elements incorporated must be distributed equally throughout the mass, is not frequently met with in autogenous welding; it is produced so rarely that we need only mention it.

MODIFICATION OF MECHANICAL PROPERTIES.

The mechanical properties of metals : tenacity, hardness, ductility, malleability, strength, etc., vary according to their temperature, their molectilar constitution, and the internal strains localised at certain points of the articles considered.

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