352 TOOL STEEL FOR THE UNITED STATES NAVY. 



After the heat treatment the tools are ground to the No. 30 Sellers 

 system of lathe tool forms and later tested on a nickel -steel forging. All 

 tools of a selective test are tested on one forging because it has been impos- 

 sible to obtain nickel-steel forgings of identical characteristics chemically 

 and physically. The depth of cut, feed and cutting speed are constant 

 throughout a selective test so that the principal variable is the elapsed time 

 of run, or the cutting Hfe of the tools. All tools are tested to destruction, 

 after which they are reground and retested until each tool has been tested 

 three times. 



The action of the tools when cutting is very interesting, indicating 

 that the material is torn from the forging instead of being cut. The chip 

 wears at first a depression in the face of the tool back of the cutting edge, 

 and the heat generated by the friction of the chip softens the tool. The 

 generation of heat and wearing away of the tool continue until the depres- 

 sion, increasing in size, finally reaches the cutting edge, which suddenly breaks 

 down and concludes the test for that tool. The action of the chip is shown 

 on Plate 137. It is necessary to grind off about ^ of an inch from the top 

 and end of the tools to remove the effects of heating. 



A volt meter and ammeter were used and later a graphic watt-meter to 

 determine the input to the motor of the test lathe. By this means the 

 average watts of the friction and cutting loads, which were found to be 

 nearly constant, were determined; the difference being the net watts which, 

 multiplied by the elapsed time of run of the tool in minutes, gave the work 

 done by the nose of the tool measured by the resistance the forging offered 

 to it. 



The elapsed time of run for a tool depends somewhat upon the dissi- 

 pation of heat generated by the friction of the chip. The dissipation is 

 accomplished by conduction in the tool and forging and by radiation, since 

 no lubricant is used. It has been noted generally that the steel forgings 

 on which the tools are cutting will heat up considerably if they are of small 

 diameter and operated at a high number of revolutions per minute. The 

 elapsed time of run decreases as the temperature of the forging which the 

 tool is cutting increases, and tests made when the room temperatures are far 

 apart are not readily comparable. Also, due to the differences in the test 

 forgings used, the selective tests conducted from time to time are not readily 

 comparable. 



Carbon Tool Steels. — Each sample submitted for selective test under 

 Schedule 4469 was tested to determine the decalescent point. The heating 

 and cooling curves are given on sheet No. 1521, Plate 144. All tools were 

 heated to a temperature slightly above the decalescent point and quenched 



