ON THE INFLUENCE OP CARBON, ETC., ON STEEL CORROSION. 80 



of carbon percentage upon the solubility in 1 per cent. H 2 S0 4 reveals 

 very important differences. In the curves given by these experimenter? 

 no peak is observed at 0"22 per cent, carbon owing to the absence oi 

 any steels between 0"14 per cent, and 0'30 per cent, carbon, and it 

 is interesting to observe that in the absence of the intermediate steel 

 (0'24 per cent, carbon) in this series, the abrupt peak at 0'22 per cent, 

 carbon would have been entirely eliminated. In connection with this 

 point it may be well to remark that careful microscopic examination 

 fails to reveal any abnormalities in any of the microstructures of the 

 steels employed in this range of composition. A more important 

 divergence, however, arises in the suggestion by these authors that the 

 maximum solubility occurs at a ' medium proportion of carbon ' — 

 presumably about 0"4 per cent, to 0'5 per cent, carbon. This is 

 completely negatived by these results, and in view of the fact that the 

 steels employed by Heyn and Bauer in this range of carbon percentage 

 also contain over 1 per cent. Mn, it appears probable that this factor 

 has exerted much more influence than was supposed by the authors 

 themselves. 



The tempered steels show a rapid rise in solubility with rise of 

 carbon from O'lO per cent, to 0"30 per cent. This rise is followed 

 by a range from 0'30 per cent, to 0'55 per cent, carbon, in which the 

 solubility remains constant in the case of the specimens tempered at 

 500° 0., and decreases in that of the specimens tempered at 400° G. 

 After 0*55 per cent, carbon a very rapid and regular rise in solubility 

 occurs with rise of carbon to 0'96 per cent., the values given in the 

 latter half of this range being higher than those given by steels of any 

 other composition or treatment. 



In the case of the hardened steels, the carbon tends to exert a 

 similar type of influence to that described in the steels tempered at 

 400° C, this fact being more evident in the 1 per cent. HC1 results 

 than in the 1 per cent. H,S0 4 results shown. The variations with 

 carbon percentage, however, are very much less pronounced, and the 

 total rise in solubility from 0*10 per cent, to 0'96 per cent, carbon is 

 very small. In connection with the influence exerted by the con- 

 dition of the carbide it is found that the conversion of the pearlite to 

 hardenite considerably decreases its solubility (in both acids) as com- 

 pared with all the varieties of pearlite. Little decisive difference is 

 observed between the steels containing the laminated and diffused 

 varieties of pearlite, whilst the resolution of the normal pearlite into 

 the emulsified variety results in a decreased solubility below 0"2 per 

 cent, to 03 per cent, carbon and a greatly increased solubility in the 

 upper part of the range above 0"7 per cent, carbon. 



Determination of Solution Pressures in Acid Solutions. 



The solution pressures in 1 per cent. H 2 S0 4 after twenty-four 

 hours' immersion have also been determined, and these results (shown 

 in fig. 3) again indicate the influence exerted by the carbon to be of 

 two main types. 



In the annealed, rolled, and normalised steels — taking e.m.f. in 

 volts and carbon percentage as co-ordinates — two distinct maxima 



