268 Transactions of the Society. 



An examination of the test-pieces after fracture proves rather 

 interesting (fig. 4), although the distinctive features are ditlicult 

 to reproduce photographically. However, the superficial appear- 

 ance of the cylindrical portions of the two tests is given fair 

 rendition, although the fractures are not so distinctive as in 

 the originals. It will be noted that the fracture of No. 4 is of 

 greater uniformity than the smaller No. 3 above it, and it was of 

 the dark grey " silky " character, which is much more satisfactory 

 in the hypo-eiitectoid steels, seeing that it indicates that the steel 

 has received reasonably correct treatment during manufacture. 



The smaller fracture shows a darker area, the sulphur segre- 

 gation thus again announcing its presence. Apart from this, the 

 fracture was of a different order, which gave an inkling of additional 

 irregularities, which were afterwards verified by the microscope. 



Drillings were then taken from three positions for analysis, and 

 the results from the head showed the sulphur and manganese to be 

 in excess, which could be expected seeing that particular care was 

 observed to obtain drillings from the segregated area. The chemical 

 composition was : — 



4-65 p.c. FejC 0-21 p.c. FeSi^ 



l-'JO „ MD3C 0-44 ,, MnSi 



0-56 „ Fe^P 92-24 „ Fe (dif.) 



And from this we can arrive at the approximate microstructure 

 of the steel. The cementite contains the FcaC plus the MngC, and 

 the FcgP and the FeSia are contained in the feriite, wliilst situated 

 somewhere in the structure is 0*44 p.c. of MnS aS " enclosures " of 

 non-metallic nature. Hence we get: — 



6 '55 p.c. Cementite 



0*44 ,, MnS (enclosed impurities) 



In hypo-eutectoid steel the pearlite (so termed from its 



" pearly " appearance when viewed under oblique lighting) is the 



strengthening constituent. Under high magnification it is seen to 



be composed of alternate plates of cementite and ferrite ; at lower 



magnifications, however, it appears as a dark area in the ferrite. 



The total pearlite is represented by eight times the percentage of 



cementite. Although this factor has not been definitely decided 



on so far, I think we can accept it as being quite near enough 



for our purpose, and so from the above we may expect to find 



approximately — 



52 • 40 p.c. Pearlite 

 0'44 ,, MnS (enclosed impurities) 

 55-16 „ Ferrite 



100-00 



Theoretically, in the presence of such a high percentage of 

 manganese, all the sulphur present in E. 288 should be in the 



