DEVELOPMENT OF MAGNETIC SUSCEPTIBILITY IN 



MANGANESE STEEL BY PROLONGED HEAT 



TREATMENT. 



By CHARLES F. BRUSH. 



(Read April 19, 1918.) 



During the past three years I have had the honor of presenting 

 several papers on " Spontaneous generation of heat in recently hard- 

 ened steel,"^ showing that all the specimens treated spontaneously 

 generated heat in easily measurable quantity after hardening by 

 quenching in water at various temperatures above the critical tem- 

 perature of decalescence. Carbon tool steel, " high-speed " tungsten- 

 chromium steel, and several specimens of nickel-chromium steel 

 were tested. In all cases the generation of heat was most pro- 

 nounced immediately after quenching and diminished rapidly, 

 though it continued observable a week or more. Generation of heat 

 was always conditional on true hardening, by quenching at a tem- 

 perature above the critical point, except in the case of one of the 

 nickel-chromium specimens. Here moderate, but unequivocal, gen- 

 eration of heat followed quenching at a temperature just helow the 

 critical point, reached by falling slowly from a higher temperature 

 through full recalescence. While true hardening could not have 

 occurred, yet there was a well-marked " stiffening " or incipient 

 hardening of the metal as shown by subsequent hardness tests. 

 When, however, the same steel, after annealing, was slowly raised 

 to the same temperature (but not above) and quenched, no genera- 

 tion of heat followed. In this connection another interesting phe- 

 nomenon developed as follows: When the same lot of nickel-chro- 

 mium steel, after annealing, was quenched at several successively 

 higher (rising) temperatures, but all below the critical temperature, 



■^Proc. Am. Phil. Soc, Vol. LIV., No. 217, May-July, 1915. Phys. Re- 

 view, N. S., Vol. IX., No. 3, March, 1917. Proc. Royal Soc, Series A, Vol. 

 93, No. A, 649, Apl. 2, 1917. Joint paper with Sir Robert Hadfield. Proc. 

 Am. Phil. Soc, Vol. LIV., No. 4, I9i7- 



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