TOOL STEEL FOR THE UNITED STATES NAVY. 351 



Observations, therefore, which were considered to be not fairly representa- 

 tive, were rejected. 



The specifications, Appendix C, contain a tungsten tool steel, class 2, 

 which was intended as an intermediate tool steel between the carbon tool 

 steel, class i, and the tungsten tool steel, class i, but it was omitted from the 

 specifications, Appendix D. A small quantity of tool steel under these spe- 

 cifications had, however, been purchased, and in order to learn how it com- 

 pared with the tool steels tested under the above selective test, milling cutters 

 were made, treated and tested under identical conditions. 



The data of the selective tests, the chemical compositions and the rela- 

 tive values computed for the above classes of carbon tool steel are given on 

 sheet No. 1521, Plate 144. 



DESCRIPTION OF SELECTIVE TESTS. 



Tungsten Tool Steel, Class i. — The five tools made from the sample bars 

 are stamped with the schedule number, with an index number which is 

 assigned to each sample, and with consecutive numbers for the tools of one 

 sample. All tools are hand-forged to the No. 30 lathe tool form of the 

 Sellers system of tool forms. The following day the tools are treated, two 

 furnaces being required for this purpose. In one furnace a temperature of 

 1,600° to 1,700° F., and in the other a temperature of 2,400° to 2,450° F., are 

 maintained. The cutting ends of the tools are uniformly heated in the low- 

 heat furnace and then in the high-heat furnace. The temperatures given 

 above do not indicate the temperature of the cutting end of the tool because 

 the temperature is lower there than where the thermo-couple is. Uniform heat 

 treatment is difficult to attain owing to the existence of a temperature gradi- 

 ent in the tool itself and the heat loss through the opening of the furnace for 

 the insertion of the tool, resulting in a sharp temperature gradient at the 

 opening of the furnace. In order to reduce the heat losses and the tempera- 

 ture gradient to a minimum and to obtain a satisfactory temperature for 

 treating the cutting end of the tool, it is necessary to close with bricks the 

 opening into the furnace so that it is just large enough to admit the tool. 

 After the tools are removed from the high-heat furnace they are cooled by 

 dipping the cutting end into oil, or they may be cooled by directing on it a 

 heavy blast of compressed air. The oil is agitated by compressed air and 

 is cooled to maintain a constant temperature. Oil was used for these tests 

 and is considered preferable because it is less noisy and less expensive than 

 compressed air, and tests which have been made indicate that better results 

 are obtained by oil cooling. The tools are cooled in the oil until they aie 

 black hot, when they are removed and placed on a cooling table. 



