146 Proceedings of Indiana Academy of Science 



Figure 2b, shows the high-phosphorus insert. Here again the 

 extent to which the phosphorus had penetrated into the steel is marked 

 by a zone of cementite. This was heated at 900 for two hours. 



The other steel inserts containing manganese, copper, chromium, 

 titanium, and sulphur showed this tendency to cause cementite segrega- 

 tion to only a very limited extent or not at all. 



Figure 2, c and d, respectively, show the specimens containing 

 alumel and copel inserts. Cementite has collected about the insert in 

 both cases. These specimens were etched with sodium picrate which 

 causes cementite to appear dark. 



From the results of these few experiments it would seem that 

 inclusions in hyper-eutectoid steel must have a certain slight solubility 

 in the austenite at high temperatures, and that the concentration of 

 the dissolved matter is therefore greatest in the immediate vicinity 

 of the inclusion. Such a condition of localized dissolved impurities prob- 

 ably has the effect of starting cementite crystallization first about the 

 inclusion, thus breaking down the state of cementite supersaturation 

 that always occurs in hyper-eutectoid steel cooling through the critical 

 range. And since each inclusion is a center of contamination and fur- 

 nishes a continuous supply of impurity to the surrounding steel no 

 amount of heat treatment can eliminate its effect. 



