For the average grade of the best High Speed Steel containing from 16% to 18% tungsten, the tool should be brought very slowly up to a dull cherry red. It is usually considered good practice to first place the tool near or on top of the pre-heating furnace before actually placing it in the pre-heater, in order that the heating might be effected just as slowly as possible. The pre-heating operation should bring the tool up to about 1600 to 1800 degrees Fahrenheit, after which the tool should be placed in the high heating furnace and brought up to 2300 to 2400 degrees Fahrenheit, or a white sweating heat. Care should be taken not to allow the tool to remain in this condition for more than an instant, as it is then in a very critical condition and could be easily burned or ruined. Therefore, the tool should be immediately pulled from the furnace and plunged into a good clean oil bath, keeping it constantly in motion. As High Speed Steels are air-hardening steels, it is also the practice to harden these steels by simply placing the cutting edge in an air blast, which produces maximum hardness in the desired point and allows the body of the tool to cool at a little slower rate, thus slightly relieving the cooling strains and producing a little less brittleness therein. Such cooling strains can be relieved throughout the whole tool by drawing the same back to about 400 to 500 degrees Fahrenheit, and sometimes as high as 1050 degrees Fahrenheit, depending upon the particular tool and its use. The treatment of Carbon Steels varies with each particular brand. Great care must always be taken to heat the steel uniformly, as a material which is heated unevenly will expand and contract unevenly and, in consequence, will crack when quenched. The steel should always be hardened on the rising heat, in general bringing the same slowly up to a dull cherry red, or to about 1450 degrees Fahrenheit, and then quenching in clear cold water, keeping the same in motion until the steel is cold. The temper should then be drawn according to the purpose of the tool, which could only be discussed for each particular case. The following range of temperatures are interesting, as being approximately indicated by the thin film of oxide tints which occur on the tool undergoing a tempering operation: Pale Yellow 428 Degrees Fahrenheit Golden Yellow 469 Degrees Fahrenheit Purple 531 Degrees Fahrenheit Bright Blue 550 Degrees Fahrenheit Dark Blue 601 Degrees Fahrenheit CONCLUSION. The effects of annealing, rolling, hammering, treating and tempering are best understood by those manufacturers who make a specialty of supplying a high grade tool steel, and in general it would be well if customers would consult freely with the producers of these steels, before attempting the delicate undertaking of Heat Treatment. CHAPTER VI. WHAT TOOL STEEL IS DOING TOWARDS WINNING THE WAR.