446 abstracts: metallurgy 



METALLURGY. — The effect of rate of temperature change on the 

 transformations in an alloy steel. H. ScoTT. Bur. Stand. Sci. 

 Paper No. 335. Pp. 91-100, figs. 7. 1919. 



Cooling curves taken on an air-hardening steel of the high speed 

 tool steel type show two critical points on cooling from 920° C, one 

 occurring at about 750° C. accompanied by the precipitation of the hard- 

 ening constituent, the carbide, and the other on fast cooling at about 

 400° C. under which condition the carbide remains in solution as 

 martensite. On cooling at intermediate rates both transformations 

 are observed and the constituents, troostite and martensite, are de- 

 tected by the microscope. A transformation is observed on the heat- 

 ing curves taken following a fast cooling which is manifested by an 

 evolution of heat ending at about 645° C. and which represents the 

 precipitation of the carbide held in solution by previous rapid cooling. 

 The resolution of the carbide under these conditions occurs at a tem- 

 perature some 10 to 15° C. higher than after a slow cooling. 



The conclusions drawn support the twenty-year-old theory of Le 

 Chatelier that^martensite is a solid solution of carbide in alpha iron. 



H. S. 



