BRUSH— GENERATION OF HEAT IN STEEL. 361 



First {Original) Hardening. — Quenched at very high tempera- 

 ture. Temperature and hardness not then observed. Large gen- 

 eration of heat, as shown in upper curve of Fig. 2. Scleroscope 

 hardness, recently observed, 79. 



Second {Recent) Hardening. — Quenched at 802°, considerably 

 above decalescence, but much lower than in first hardening. Com- 

 plete loss of magnetic susceptibility occurred at 765°: Good gen- 

 eration of heat, but very much less than in first, as shown by the 

 lower curve of Fig. 2. For convenient comparison with this curve 

 the normal cooling curve is shown as a dotted line appropriately 

 located. Hardness was now 73. 



Third Quenching. — Heated to 815°, somewhat above preceding 

 quenching temperature, allowed to cool slowly to 720° and quenched. 

 This was a little below the temperature of complete recovery of 

 magnetic susceptibility, which had occurred at /2Q°. Hardness was 

 now only 28.5, and there was no generation of heat. (The nickel- 

 chromium steel had shown good generation of heat under similar 

 circumstances.) Note the small temperature diiTerence, 36°, be- 

 tween complete loss and complete recovery of magnetic susceptibility. 

 Annealed by heating to 822°, to obliterate previous quenching 

 effects, and cooling slowly in furnace. Hardness was now 25.5. 



Fourth Quenching. — Heated slowly, from annealed condition, to 

 633° (considerably below the lower critical temperature) and 

 quenched. Hardness was again 28.5, and there was no trace of 

 absorption of heat. (The nickel-chromium steel had shown good 

 absorption of heat under similar circumstances.) 



Fifth Quenching. — Heated slowly to 732°, just above the tem- 

 perature of complete recovery of magnetic susceptibility, and 

 quenched. No generation or absorption of heat, nor change in 

 hardness (28.5). 



Clearly, the carbon steel showed none of the excentricities of the 

 nickel-chromium steel when quenched below the hardening tempera- 

 ture. But when quenched a little above, as well as far beyond this 

 temperature, they behaved very much alike. 



While considering plain carbon steel, I thought it worth while to 

 observe heat generation in some steel (or wdiite cast iron) very 

 high in combined carbon, and very pure otherwise, which I happened 



