Scott. — Resistance of Steel to Mechanical Shock. 523 



carbide Fe 3 C, separates out alongside the ferrite, forming the 

 eutectic of iron and carbide of iron known as " pearlite." We 

 thus have as the final condition of our material ferrite-crystals 

 imbedded in a matrix of pearlite which itself consists of an 

 intimate mixture of iron and carbide of iron. 



When the steel contains above 035 per cent, of carbon 

 the Ar 3 and Ar 2 points are merged in one. 



A steel containing - 9 per cent, of carbon is of eutectic propor* 

 tions : there is consequently only one point of retardation — 

 the Ar or carbon point, at 780° C. — and no separating-out of 

 ferrite crystals, the resulting steel being wholly pearlite. 

 If the steel contains more than 9 per cent, of carbon, still fol- 

 lowing the analogy of the salt-and-water solution, the carbide 

 Fe 3 C (cementite) first forms, then the pearlite, and the re- 

 sulting steel consists of cementite in pearlite with no free ferrite- 

 crystals. 



If a steel, instead of being slowly cooled, is quenched from 

 a temperature the value of which is disputed, but which the 

 writer considers it rational to suppose should be just above the 

 Ar 3 point, and hence dependent on the percentage of carbon, 

 no time is given for the changes, indicated by the curves, to 

 occur, and the material is retained in practically the same state 

 as it was in at the quenching-temperature, the carbon remain- 

 ing in its diffused or hardening condition. Steel so treated is 

 fully hardened. To such quenched steel the name of " martens- 

 ite " is given ; if of eutectic proportions, " hardenite." 



Fig. 6. 



Fern he 



ensife 



1-4 CarBon percenf. 



Cemenhhe 



The diffusion of carbon in steel has never been better illus- 

 trated thao by an experiment performed last year by Mr. Stead. 

 Six bars of varying carbon content were made coarsely crystal- 

 line by very slowly cooling down in the heart of a ladle of molten 



