I have indicated in a foregoing chapter the growing use of manganese and chrome steel for grinding balls in tube mills as well as their use for linings. It is therefore important that the student or operator should be conversant with the qualities imparted to steel by the addition of quantities of the various substances now used in " alloy steels".

If we consider the various stresses to which crushing machines are subjected we readily appreciate the fact that some attention should be given to the study of the various alloy steels now coming into use. We should not be led to believe that their use is a remedy for all evils for both wrought iron and carbon steel are more suitable for some classes of work than any mixtures of steel with manganese, nickel, chrome, tungsten or vanadium.

Most steels contain a small percentage of manganese by reasons of the methods of manufacture, so that this element is a basic constituent of steel and until this amounts to over 2 per cent., the product is still carbon steel. Over this amount we have manganese steel, but the real manganese steel contains over 6 per cent, manganese for between 2 and 6 per cent, the alloy is so brittle as to be worthless from an economic point of view.

Owing to the ease with which some of the elements enter the slags, it is difficult to keep to a fixed percentage of the element within narrow limits. In the manganese alloys containing 10 to 15 per cent., when made in large quantities by the openhearth process, the manufacturers require a limit of at least lj^ percent., up and down. On account of the difficulty of decarburizing the raw products containing the alloy element, it is not commercially profitable to fix the carbon content, this being approximately regulated by the amount of carbon in the steel before the addition of the alloy element, and by that contained in the alloy iron. For example, ferromanganese containing from 60 to 80 per cent, manganese, has a carbon content of 6 to 6.50 per cent., and while the carbon content in the steel, before adding the ferromanganese, may be lowered to under 0.10 per cent, carbon, yet it must take in the carbon of the ferromanganese when this is added. The above inference pertains to steels made by the openhearth or Bessemer processes; those made by the crucible and electro-smelting processes are more even in composition, and can be duplicated within very narrow limits.

It appears that steel is a nicely balanced product, in which any increase in any one physical quality is compensated by a decrease in some other quality. For example, when we increase its tenacity by the addition of some element such as carbon, we decrease some other quality, such as its ductility or elasticity. With plain carbon steel, an increase of carbon up to a certain maximum, increases the tensile strength, likewise the hardness, but at the same time it decreases the ductility until this becomes nil. This may be seen by consulting the graphs.

The curious feature in respect to the alloy steels is that the increase and decrease of the physical qualities follows no definite rule, so one cannot predetermine qualities of steel containing a certain per cent, of the alloy element, from a knowledge of what the qualities were when a different proportion of this element is used. It is therefore a question for experiment to determine the physical qualities of alloy steels, with different percentages and combinations of the alloy.