The principal use of tungsten is in high-speed tool steel, but here a high percentage of manganese is distinctly detrimental, making the steel liable to fire crack, very brittle and weak in the body, less easily forged and annealed. Manganese should be kept low and a high percentage of chromium used instead. Tools of tungsten-chromium steels, when hardened, retain their hardness, even when heated to a dark cherry red by the friction of the cutting or the heat arising from the chips. This characteristic led to the term "red-hardness," and it is this property that has made possible the use of very high cutting speeds in tools made of the tungsten-chromium alloy, that is, "high-speed" steel. Tungsten steels containing up to 6 per cent do not have the property of red hardness any more than does carbon tool steel, providing the manganese or chromium is low. When chromium is alloyed with tungsten, a very definite red-hardness is noticed with a great increase of cutting efficiency. The maximum red-hardness seems to be had with steels containing 18 per cent tungsten, 5.5 per cent chromium and 0.70 per cent carbon. Very little is known of the actual function of tungsten, although a vast amount of experimental work has been done. It is possible that when the effect of tungsten with iron-carbon alloys is better known, a greater improvement can be expected from these steels. Tungsten has been tried and is still used by some steel manufacturers for making punches, chisels, and other impact tools. It has also been used for springs, and has given very good results, although other less expensive alloys give equally good results, and are in some instances, better. Tungsten is largely used in permanent magnets. In this, its action is not well understood. In fact, the reason why steel becomes a permanent magnet is not at all understood. Theories have been evolved, but all are open to serious questioning. The principal effect of tungsten, as conceded by leading authorities, is that it distinctly retards separation of the iron-carbon solution, removing the lowest recalescent point down to atmospheric temperature. A peculiar property of tungsten steels is that if a heating temperature of 1,750 deg.F. is not exceeded, the cooling curves indicate but one critical point at about 1,350 deg.F. But when the heating temperature is raised above 1,850 deg.F., this critical point is nearly if not quite suppressed, while a lower critical point appears and grows enormously in intensity at a temperature between 660 and 750 deg.F. The change in the critical ranges, which is produced by heating tungsten steels to over 1,850 deg.F., is the real cause of the red-hard properties of these alloys. Its real nature is not understood, and there is no direct evidence to show what actually happens at these high temperatures.