TOOL STEEL EOR THE UNITED STATES NAVY. 355 



The pneumatic chisels were operated by a man, which, of course, intro- 

 duced a greater variation than if a machine were used. The question as 

 to whether or not the test should be stopped, due to the condition of the 

 tool, is sometimes a matter of individual opinion, such as to the degree of 

 dullness, or the amount of reduction in width of cutting edge due to wearing 

 of the sides. 



The treating temperature for the tungsten tool steel, class i, can be 

 varied through a short range in the vicinity of 2,250° F., without producing 

 much variation in the results of the physical test. The treating temperature 

 of the carbon tool steels seems to be within narrower limits, which may 

 perhaps account for some of the variations in the test. It is, of course, 

 extremely difficult to hold the furnaces, which are of the oil-burning type, to 

 absolutely definite temperatures. 



The test of the carbon tool steel, classes i and 2, which contained tung- 

 sten, showed less variation than the carbon tool steels, as may be seen by 

 referring to sheet No. 1521, Plate 144. This may indicate that the addition 

 of tungsten increases the treating temperature limits slightly without affect- 

 ing the results of the physical test very much. The addition of tungsten 

 seems to produce two desirable results : increasing of the cutting life of the 

 tools and increasing the treating temperature limits of the tool steels. 

 Furthermore, the tool steel containing this element apparently does not 

 require any different method of treating from that in general use for carbon 

 tool steels. 



A test was made of tools from Schedule 3244 to determine the relation 

 between the cutting speed and the elapsed time of run, or cutting life of the 

 tool, all conditions being maintained constant except cutting speed. The 

 curve obtained from this test is shown on sketch No. 288, Plate 140. 



Photomicrographs have been made of all the tungsten tool steel, class i, 

 tools used in the selective test for Schedule 4469 by the Naval Experiment 

 Station, Annapolis, Md. Two photomicrographs were taken of the top face 

 of each tool, one near the end where the chip rubbed, which has been 

 marked "A," and the other a short distance back which has been marked 

 "B." The following photomicrographs, shown on Plate 139, were made of 

 tools after the selective test had been completed and the surface from 

 which they were taken is about f -inch below the siurface exposed to the fur- 

 nace heat : — 



Card No. 4, B 2, from tool No. 1-2. 



Card No. 8, B 4, from tool No. 2-4. 



Card No. 4, B 2, from tool No. 3-2. 



Card No. 5, A 3, from tool No. 4-3. 



