Soft-centre Steel
Bar steel with a hard surface enclosing a tough centre core of mild or soft steel. This steel is used especially for making articles that, besides having a hard-tempered surface, must possess the strength of mild steel. The mild-steel ingot is cast, hammered down, and treated in the cementation-furnace until the surface has been carburized to the depth required, when it is again subjected to the process of rolling or hammering down to the size and shape of bar needed. See CEMENTATION; BLISTER-STEEL. Softeners are a class of pig iron containing such softening qualities as will destroy, or at lest neutralize, opposite qualities existing in other irons; or they may wholly consist of another metal to alloy with iron, as aluminum or aluminum ferro-silicons, etc. The softening elements in pig iron are graphitic carbon and silicon, while combined carbon, phosphorus, manganese, and sulphur may be classed as hardeners. It is an established fact that all pig irons low in the latter elements, and which are at the same time high as to the former, are recognized as softeners, because of the remarkable quality of silicon to change chemically combined carbon to graphitic carbon; in other words, changing hard iron to soft, and enabling the founder to use up large quantities of inferior irons, at reduced cost, by the simple admixture of another iron that costs no more than any other ordinary brand; and all this without any deteriorating effect on the resultant castings. See SCOTCH PIG IRON; SILICON; ANALYSIS.