HIGH SPEED STEEL, a tungsten-chromium tool steel of great importance in machining various grades of iron and steel, was developed almost simultaneously by American and European metallurgists. It is the outcome of significant research by F. W. Taylor and Maunsel White. By the Taylor-White method a heat treatment was developed which applies substantially to all the "high speed" steels. It consists of two essential parts : (a) heating the forged tool unusually hot (in fact, until the sharp edges start melting and appear to sweat) and then cooling in oil or an air blast, (b) reheating in a lead bath at 62 5 ° C and cooling in air. Such combination of high-quench and high-draw induces the quality of "red-hardness" in these high alloys, whereby the tool retains its useful hardness even when working so fast that the tip is heated red-hot by friction of the chip.
When given the Taylor-White heat treatment such improved steels cut at iooft. per minute, whereas carbon steels formerly used did not exceed i6ft. per minute. The addition of about one per cent of vanadium, due to the work of John A. Mathews, marks a further step. High speed steel with properly adjusted chemical analysis, made with utmost care in the steel mill, properly shaped and hardened, produces tools capable of cutting at a speed greater than 15oft. per minute. A ten-fold increase in machinery speed was thus accomplished between 1875 and 1915. Up to 5% cobalt has been usefully added to improve strength and hardness of both high and low tungsten varieties and enable them to cut previously "non-machinable" metals like Hadfield's manganese steel. A more important innovation consists of replacing half or more of the tungsten with molybdenum, an element analogous chemically, but cheaper and much more readily available. • Current developments are aimed at perfecting variations of the main steels to adapt them for special services. The variety most used is the "18-4—I" analysis shown in the first column below. Low-tungsten tools, shown in second column, are preferred in America for deep cuts on rough f orgings ; this is probably more popular in Great Britain for general purposes than the high tungsten variety. A theoretical study of the Taylor-White method of heat treatment is difficult and cannot be given in this article.