What is an alloy steel? The general definition of an alloy steel is, “a solidified solution of two or more metallic substances”. The International Committee upon the nomenclature of iron and steel defines alloy steels as “those steels which owe their properties chiefly to the presence of an element (or elements) =other= than carbon”. This latter definition more nearly applies to our case, but it must be born in mind that the distinction between an element added merely to produce a slight benefit to ordinary carbon steel, and the very same element added to produce an alloy steel itself, is sometimes a very delicate one. For example: Manganese is added in amounts usually less than 1.50% to all Bessemer and Open-Hearth Steels, for the purpose of getting rid of oxygen, and neutralizing the effect of the sulphur. But this does not produce an Alloy Steel. When we make “manganese steel” containing 10 to 20% manganese, the material then has properties quite different from the same steel without the manganese, and we then have a Manganese Alloy Steel. Thus, for our purpose, we may consider an alloy steel as being one to which some element =other= than carbon has been added in sufficient amount to materially affect the physical properties which the steel will have when hard. HIGH SPEED STEELS. High Speed Steels are perhaps the most important of alloy steels, and derive their name from the fact that they can be used as cutting tools when the cut on the machined member is being made at a high speed. This, of course, subjects the tool to severe operating conditions, which simple carbon steels could not stand. These steels have other notable characteristics, among which is that of “self-hardening” or “air-hardening”, as it is sometimes called. This means, when the steel cools naturally in the air, from a red heat or above, it is not soft like ordinary steel, but is hard and capable of cutting other metals. Another striking characteristic of high speed steels is their ability to maintain a sharp cutting edge while heated to a temperature far above that which would at once destroy the cutting ability of a simple tool steel. Because of this property, a tool made of high speed steel can be made to cut continuously at speeds three to five times as great as that practicable with other tools. The result of the friction of the chip on the tool may cause the tool to become red hot at the point on top where the chip rubs hardest, and the chip may, itself, by its friction on the tool, and the internal work done on it, by upsetting it, be heated to a blue heat, or even hotter. ELEMENTS WHICH OCCUR IN ALL STEELS. There are certain elements which are practically always found in =any= kind of steel. These elements are capable of producing many varied effects on the finished product. They are Iron, Carbon, Manganese, Silicon, Phosphorous and Sulphur. IRON.