THE HARDENING OF STEEL 69 



retained in the condition of structure which it 

 possessed at the moment of quenching. The high- 

 temperature structure as it exists above a critical 

 point can thus be more or less completely pre- 

 served by quenching and can then be studied at 

 leisure. But by thus preserving the structure 

 which the metal possesses naturally at a high 

 temperature, and by rapid cooling preventing the 

 transformation which it would undergo if cooled 

 slowly, we also preserve to some extent the physical 

 properties corresponding to that high-temperature 

 condition. The most striking case of this kind is 

 that of steel containing something like one per 

 cent, of carbon which undergoes the violent heat- 

 evolution during cooling to which we have already 

 referred. If this steel is allowed to cool slowly 

 and to undergo the transformation from which 

 that heat-evolution arises, it is fairly soft and 

 tough; if, on the other hand, it is quenched in 

 water from a red heat, in such a way as to suppress 

 as completely as possible that same transformation, 

 then the steel is extremely hard and brittle, and 

 we find a corresponding difference in the micro- 

 structure. To this extent the New Metallurgy has 

 afforded an "explanation" of the oldest of metal- 

 lurgical mysteries the hardening of steel. But 

 this is only a particularly striking and familiar case 

 of what is really a widespread class of phenomena. 

 The thorough scientific investigation of all these 

 phenomena is one of the tasks which the New 



