552 



TRANSACTIONS OP SECTION B. 



by Messrs. Wilson, Pease and Co. and Messrs. Cochrane and Co., Middles- 

 brough. They were made from Cleveland ironstone and contained : — 



It may be accepted that the sulphur in the white iron undoubtedly is the cause 

 of the whiteness of the iron, whilst the excessively high silicon and low sulphur 

 are equally responsible for the graphitic condition of the carbon in the grey irons. 



The micro-structure of the high silicon metal was characteristic of all 

 phosphoretic, high-silicon, carbon alloys. Curved plates of graphite cut the 

 mass in many directions, whilst the binary eutectic of phosphorus and iron 

 remained in irregular patches, generally midway between the graphite plates. 

 The ground mass occupying the space between the eutectic and graphite plates 

 consisted of silico-ferrite. 



The interesting feature about the structure of the white iron is that there 

 was no iron-iron-carbide eutectic. This had been replaced by the ternary 

 eutectic of iron-phosphorus and carbon, which, according to Dr. Wiist, contains 

 about : — 



Iron 



Phosphorus 



Carbon 



Per cent. 

 91 

 7 

 2 



100 



There was evidence that the primary crystals of austenite of the octohedral 

 skeleton type had been the first to fall out of solution, that the second crystal to 

 form consisted of short plates of carbide of iron (cementite) ; whilst the ternary 

 eutectic of phosphorus, carbon, and iron was the last to freeze and occupied 

 spaces between the cementite plates and the primary crystals. 



Dr. Carpenter and his assistant, Mr. Edwards, of Victoria University, 

 Manchester, kindly obtained, for the purpose of this address, the cooling 

 curves of these two typical metals. These were as follows : — 



Grey Iron. 



The long arrest at 1118° indicates a change of state, but is also coincident 

 with important chemical changes. The second long arrest at 945° is due to 

 freezing of the iron phosphorus carbon eutectic. The arrest at 850° indicates 

 the formation of peai-lite, and corresponds closely with the arrest in a similar 

 alloy examined by Gontermann. The arrest at 690° is probably due to the forma- 

 tion of pearlite in the eutectic of iron and phosphorus, and is of great interest, 

 for it points to the conclusion that silicon is not a constituent of the austenite of 

 the ternary eutectic. 



White Iron. 



The micro-structure and analysis help more fully to explain the arrests on 

 cooling this alloy. 



The first arrest at 1149° C. is where the primary austenite crystallises with 

 the silicon, as will be shown presently. 



The second arrest is where the primary cementite plates freeze. 



