Silicon
This substance is the base of silex or silica, and is now supposed to be a non-metallic element. More or less of this element is present in all varieties of pig iron, but whether in chemical combination or otherwise it has not yet been satisfactorily determined. Silicon acts to change the combined carbon in cast-iron to graphitic carbon. Describing the result of his experiments for ascertaining the influence of silicon upon cast-iron, W. J. Keep says: "We have seen, however, that a white iron which will invariably give porous and brittle castings can be made solid and strong by the addition of silicon; that a further addition of silicon will turn the iron gray, and that as the grayness increases the iron will grow weaker; that excessive silicon will again lighten the grain and cause a hard and brittle as well as a very weak iron; that the only softening and shrinkage-lessening influence of silicon is exerted during the time when graphite is being produced, and that silicon of itself is not a softener, or a lessener of shrinkage, but through its influence on carbon, and only during a certain stage, it does produce these effects."
To produce highly siliceous iron, or siliconeisen, in the blast-furnace the blast requires to be extremely hot, the furnace driven slowly, and the charges, while containing much silica, must be highly aluminous and not markedly calcareous.
When 20 per cent of silicon is present in siliconeisen the amount of carbon in the alloy is very low.
To prevent honeycombing in soft cast steel which contains very little carbon, an alloy containing 8 per cent silicon, about 15 per cent manganese, and 1.3 per cent carbon is employed extensively in some steel manufactories. The presence of silicon along with manganese acts to diminish the formation of honeycomb in steel ingots. See HONEY-COMBING; SOFTENERS; ANALYSIS.