MANGANESE Manganese.— Manganese acts in two op posite ways on cast iron. It increases the power of the iron to hold carbon in solution and conse quently tends to increase the combined carbon and hardness. It unites with the sulphur and forms a sulphide of manganese which separates out before the iron sets and thus prevents the sulphur from exerting a hardening effect. Pie iron contains from 0.2 of 1 per cent to 3% per cent manganese, while cast iron ordinarily runs from 0.1 of 1 per cent to 1 per cent in manganese. Owing to its affinity for carbon, manganese is also found as iron-manganese carbide. To this same affinity must be ascribed the fact that iron with a high manganese con tent has as a rule a high carbon content. The carbide assumes a very hard granular form causing hard spots in the iron very difficult to machine.
Condition of Manganese in Cast Iron.- Manganese exists in three conditions in cast iron. In the molten condition it tends to unite with the sulphur as manganese sulphide. As the iron cools through the critical temperature the manganese unites with the carbon to form a carbide Mn,C. Any manganese not so united alloys with the iron.
Effect of Manganese on the Properties of Cast Iron.— Manganese by its action on the carbon tends to harden cast iron, while its effect on sulphur tends to soften cast iron. Whether the hardening effect with the carbon or the softening effect on the sulphur predominates depends upon the relative amount of manganese and sulphur present.
Action of Manganese on Cast Iron.— Manganese unites with the sulphur and forms a manganese sulphide at a temperature above the solidifying temperature of cast iron. Con sequently this manganese sulphide has no more detrimental effect on the iron than so many small particles of any neutral impurity, and eventually reaches the slag, unless ferrous oxide is present. In this case it is apt to form a layer between the molten iron and the slag. Manganese therefore prevents the bad effect of the sulphur, and hence in the case of high sulphur irons it acts as a softener. However, the combination of manganese and sulphur takes place only at very high temperatures, and then but slowly, so that sufficient time must be al lowed for such cleating out of the sulphur. The manganese in excess of that which unites with the sulphur unites with the carbon to form a carbide Mn,C. This carbide hardens the iron, for it of itself is an intensely hard substance. Consult Keep, W. J.,