BRUSH— GENERATION OF HEAT IN STEEL. 



359 



this for the radically different results of the third and seventh 

 quenchings, which were made at substantially the same temperature. 

 The temperature dift'erence betw^een complete loss and complete re- 

 covery of magnetic susceptibility, 117°, was unusually large; but 

 while this temperature drop brought about almost annealed softness, 

 and full restoration of magnetic qualities, it did not very greatly 

 affect that quality of the steel, whatever it is, which is responsible 

 for the spontaneous generation of heat. Seemingly, one or more 

 of the several unstable compounds or mixtures of the constituents 

 of the steel which were formed at the upper critical temperature did 

 not have time to wholly revert to normal annealed condition while 

 the metal w-as cooling to and passing through recalescence. The 

 time of this cooling was about half an hour. 



To confirm the curious result of the third quenching, i. e., gen- 

 eration of heat without hardening, the bars w-ere quenched the eighth 

 time as follows: Slowly heated (nearly two hours) to 819°, slowly 

 cooled (nearly one hour) to 680° and quenched. During the heat- 

 ing complete loss of magnetic susceptibility occurred at 779°, which 

 was an excellent confirmation of the former finding (77y°). But 

 in cooling, full recovery of magnetic susceptibility came at 680°, 

 which is 20° higher than before. The five intermediate treatments 



Resume of Specimen B. 



Temperature of complete loss of magnetic susceptibility, 777° C. 

 Temperature of complete recovery of magnetic susceptibility, 660/680. 



may, perhaps, account for this. And this higher quenching tem- 

 perature may account for the somewhat greater hardness produced, 

 which was later found to be 47, as against 37 for the third quench- 

 ing (74 for true hardening above decalescent temperature). 



