(C 



BURGESS, CROWE, RAWDON, WALTENBERGI RAILS 353 



A particular form of this theorem, known as the principle of 

 dynamical similarity" is in familiar use for the interpretation 

 of experiments on mechanical models; but the theorem is equally 

 applicable to problems in heat and electromagnetics. 



PHYSICAL METALLURGY.— O^serwiions on finishing temper- 

 ature and properties of rails.^ G. K. Burgess, J. J. Crowe, 

 H. S. Rawdon, and R. G. Waltenberg, Bureau of Standards. 



Observations were taken with an optical pyrometer of ingot 

 and finishing temperatures of rails in four representative mills. 

 There is practical uniformity among the several mills for the 

 rolling temperatures of ingots for steel rails, the range being from 

 1080°C. (1975°F.) to 1140°C. (2085°F.). There is no very con- 

 siderable difference among the finishing temperatures of the rails 

 as observed at the hot saws for the several mills, the range being 

 about 880°C. (1615°F.) to 990°C. (1815°r.). Or, in other words, 

 the four mills all finished their rails to within 50°C. of 935°C. 

 (1715° F.) on the average. This temperature of 935°C. is 270°C. 

 (520°F.) above the mean value, 665°C. (1230°F.) of the critical 

 ranges of these rail steels. Concerning the distribution of temper- 

 ature within the head of a cooling rail, it is shown that the center 

 of the head is some 50°C. (120°F.) to 60°C. hotter than the optical 

 pyrometer reading at 935°C. ; therefore the center of the head is 

 finished, on the average, at about 325°C. (615°F.) above the critical 

 range for 100 lb. sections. 



Chemical analyses and microphotographic examinations were 

 also made and the mechanical properties determined for a number 

 of samples of rail, the rolling of which had been observed. From 

 a comparison of these few observations there appears to be not a 

 sufficient degree of correlation to warrant associating very speci- 



^ This is a summary of a paper to be published shortly in full as a Technologic 

 Paper of the Bureau of Standards with the following contents: 1. Introduction; 

 2. Importance of Limiting Temperatures of Rolling Rails; 3. Methods of Measur- 

 ing Rail Temperatures; 4. Wickhorst's Experiments; 5. Measurements of Ingot and 

 Finishing Temperatures; 6. The Samples and Chemical Analyses; 7. Mechanical 

 Properties of Rails; 8. Melting Temperatures of Rail Steels; 9. The Critical 

 Ranges of Rail Steels; 10. Observations on the Microstructure; 11. Temperature 

 Distribution in a Cooling Rail ; 12. The Expansion of Rail Steels ; 13. The " Shrink- 

 age Clause" in Rail Specifications; 14. Summary and Conclusions. 



