On the Tempering of Iron li<(i-<l< :il //// 



463 



yield-point was the same as obtained in the first test of the specimen, 

 namely, 0*13 of an inch on 4 inches. 



The material after this second overstrain was once more in a semi- 

 plastic state. A curve obtained immediately after the overstrain 

 would have been similar to Curve Xo. 2, but the loading could have 

 been continued up to 49 tons per square inch. Had the loading been 

 continued beyond this amount while the material was in the semi- 

 plastic state, large yielding would have taken place, and fracture 



DIAGRAM 1. 

 (Steel as supplied.) 



651 4 3 



Eoc tensions . / Unit 



Curve 1. Primary test. 

 2. Shortly after 1. 

 3. If days 1. 



of an inch ? ( * 



Curve 4. 2 weeks after 1. 



5. After heating to 200 = C. 

 6. ,, ,, ,, 



would have occurred at probably a very slightly increased load. Re- 

 covery of elasticity was, however, effected as before, by heating the 

 specimen to about 200' C., and allowing it to cool. It was known as 

 the result of earlier experiments* that the yield-point of the material 

 would be raised by this process through a second step of 1 1 tons, so 

 that the specimen should not yield until a stress of 60 tons had been 

 applied. 



Curve No. 6 of Diagram 1 shows that the specimen bore the stress 

 of 60 tons, but that with 60i tons per square inch, a yield-point and 

 fracture occurred. 



Diagram No. 2 shows that annealing altered in an interesting 



* IUd., p. 3i. 



