84 REPORTS ON THE STATE OF SCIENCE. 



as a base line from which the influence of other elements upon 

 the corrodibility of steel may be determined in future researches. 

 These pure iron-carbon alloys were prepared by the coke crucible 

 process in the Metallurgical Department of Sheffield University, 

 the materials employed being Swedish bar iron and charcoal, this 

 method having been found to give the purest iron-carbon alloys obtain- 

 able. Six such alloys have been employed, ranging from O'lO per cent, 

 to 0'96 per cent, carbon, and the microscopic examination in the rolled 

 condition showed the distribution of the micro-constituents in these 

 steels to be remarkably even throughout the whole of the series. It is 

 also important to note that, despite careful search, no traces were 

 found of manganese sulphide, the powerfully electropositive nature of 

 which tends to cause serious electrolytic action when present in steel, 

 thus materially increasing the corrodibility. 



The determinations of the corrodibility and other properties of 

 these steels have been carried out in several states of heat treatment, 

 which have been designed to resolve the pearlite into the principal 

 varieties in which it usually exists in carbon steels — viz. : (a) Diffused 

 (b) Laminated, and (c) Emulsified, and also into Hardenite, which is 

 the essential constituent of hardened carbon steels. The treat- 

 ments employed were (1) As Rolled, (2) Normalised, (3) Annealed, 

 (4) and (5) Hardened and Tempered at (a) 400° C. and (£) 500° C, 

 (6) Hardened. 



Determination of Simple Corrosion in Sea-water. 



The relative corrodibilities of these steels in all states of treatment 

 have been measured by immersing polished cylindrical bars of the 

 various specimens (4£ inches long x | inches dia.), each separately 

 in 700 c.c. sea-water for a period of thirteen weeks, the loss in weight 

 per cent, during this period being determined. 



The results obtained, as plotted in fig. 1, indicate that the carbon 

 exerts two types of influence upon the corrodibility, dependent upon 

 the condition of the carbide in the steel. In the rolled, normalised, 

 and annealed specimens, in which the carbide (as shown by micro- 

 scopic examination) exists entirely either as the diffused normal 

 variety, or as the laminated variety of pearlite, the corrodibility rises 

 to a maximum at saturation point (0'89 per cent, carbon), and then 

 decreases upon the appearance of cementite in the steel. The rise in 

 corrodibility in such steels with increase of carbon from O'lO per cent, 

 to 0'89 per cent, is not regular, but is much more rapid in the range 

 0'3 per cent, to 0'89 per cent, carbon than in the low carbon range 

 O'lO per cent, to 0'3 per cent, carbon. 



In the hardened and tempered specimens, however, in which the 

 carbide has been converted respectively either to hardenite or the 

 emulsified variety of pearlite, it has been found that the corrodibility 

 rises continuously from O'lO per cent, to 0'96 per cent, carbon, no 

 maximum being observed at the saturation point. The proportional 

 increase of corrodibility in these steels with rise of carbon per cent, 

 is very rapid up to about 0'25 per cent, carbon in the case of the 

 hardened steels, and about 0'40 per cent, carbon in the tempered 



