614 



Professor J. 0. Arnold 



[Jan. 24, 



The recalescence results obtained are of great practical as well 

 as' theoretical interest. They strongly suggest the explanation of 

 the curious thermo-mechanical behaviour of high-speed steels, and 

 incidentally they appear to provisionally prove that the harden- 

 ing is not due to allotropic change, but to the carbon change only. 

 The slide on the screen (Fig. 10) shows (1) the inverse rate re- 

 calescence curve of a 0*2 per cent plain carbon steel which exhibits 

 all Osmond's critical points, viz. Arg, Ar._, (with a double peak), and 

 Ar^, the carbon change point ; (2) the recalescence of a saturated 

 steel containing • 89 per cent of carbon, in which all three points 

 are merged into one very large evolution of heat at 695° C. ; (3) 

 the recalescence curve of a steel containing 1 • 1 per cent of carbon 

 and 10 "3 per cent of vanadium. This curve was registered from 

 1210" to 500° C. It presents only the double-peaked point Ar2. 

 When the steel is quenched all along the above range it still remains 

 quite soft to the file. To harden it, it is necessary before quenching 

 in water to heat the alloy above the A^ or carbon change point, 

 which takes place at a white heat, near 1400' C. The steel is then 

 very hard. 



The micrograph on the screen (Fig. 9) shows the transformation 

 on heating up to a white heat (a) of annealed vanadium cementite 

 into sorbitic vanadium pearlite, (b) of sorbitic vanadium pearlite into 

 amorphous and topaz-hard vanadium hardeuite. 



The final slide (Table III.) exhibits the advance in concrete- 

 cutting efficiency of turning tools from 1740 to 1912. It will be 



TABLE III. — Comparative Cutting Powees of Tuening-Tool 

 Steels feom 1740 to 1912. 



Type of steel 



Huntsman's 



Low-grade 

 speed 



Cubic Inches 



removed 



Caeteris imrdjus 



16 



high 



Type of Steel 



Huntsman's 

 High-grade high 



Culiic Inches 



removed 

 Caeteris imrihu 







700 



noted that. the best steel of this kind made in Sheffield in 1740 would 

 be absolutely incapable of cutting at all under conditions under 

 which the best modern high speed steel would remove 700 cubic 

 inches of metal before breaking down. 



The advantages of this enormous increase in cutting power are 

 manifold, and an obvious example is the relative rapidity with which 

 huge naval guns may now be turned out. 



In January 1909 1 had the honour of suggesting to a lioyal 

 Institution audience the coming of a new British steel, which would 



