| Silicon | < .02 |
| Phosphorus | < .01 |
| Sulphur | trace |
can hardly be bought for less than 5 cents a pound.
This difference of three cents a pound is justifiable when the highest grade of tool-steel is to be made; and it would be silly to require any such material in any spring, machinery, or structural steel.
In addition to these impurities there are other difficulties to be guarded against, chief among which is an uneven distribution of elements.
In all steel there is some segregation; that is to say, as the liquid metal freezes, the elements are to some extent squeezed out and collected in that part of the ingot which congeals last. It is claimed that in the Bessemer and Open-hearth processes any ferro-silicon added to quiet a heat, or any ferro-manganese added to remove oxygen, are at once absorbed and distributed through the mass, and so when any serious irregularity is discovered it is charged to segregation.
A heat may produce billets of 75 carbon and 120 carbon, and again it is called segregation.
As a rule, inertia has more to do with such differences than segregation. One crucible of steel may produce an ingot containing 90 carbon and 130 carbon. Segregation has nothing to do with this: a careless mixer has put a heavy lump of 140- or 150-carbon steel in the bottom of the pot and covered it up with iron. The steel melted first and settled in the bottom of the pot, the iron melted later and settled on top of the steel, and they did not mix. The teeming was not sufficient to cause a thorough mixing.
Segregation covers a multitude of sins.
Exactly how much is sin and how much is segregation will not be known until analyses are made of the top, middle, and bottom of the bath, and of the contents of the ladle, these to be compared to analyses of the top, bottom, and middle of the ingots. There is certainly an unavoidable amount of segregation, and as equally certain an amount of curable irregularity due to inertia.