Temperature of Iron and Steel during RecaJescence. 189 



Table IV. shows :— 



(xii.) The expansion of the specimen during heating from 

 600° to 800°, and the contraction of the same during cooling 

 from 800° to 600°, diminishes in magnitude with the decreasing 

 percentage of carbon. The magnitude of the expansion 

 during heating from 0°-600° seems to be about the same in 

 the different specimens. 



The length and temperature curves in figs. 16-19 show, 

 furthermore, at what temperatures the anomalous changes of 

 length begin, and give approximate values of the magnitude 

 of the longitudinal changes per length-unit. A summary of 

 this is given in the following : — 



Table V. — Sandviken Wire. 



0-9 % O. 



0-6 % O. 



0-3 % C 



I 

 Expansion to D 00909 



0-00887 



000093 



705°-720° 



16 5 sec. 



000898 



000056 



705°-800° 



46-0 sec. 



Magnitude of contraction atD... 00054 

 Temperature of D 715°-740° 



Time of D 17 "5 sec. 





Expansion at D' 00747 



0-00635 



000138 



650°-625° 



13-0 sec. 



0-00730 

 0-00070 

 720°-645° 

 16-0° sec. 



Magnitude of expansion at D'.J 00087 

 Temperature of D' 665°-660° 



Time of D' ' 95 sec. 



! 



The appearance of the longitudinal curves characteristic 

 of the different specimens at the critical points D and D / has 

 not been noticeable, depending upon the relatively long- 

 intervals of time (6 seconds) between the respective readings. 

 The longitudinal curve for iron containing 0*3 per cent, of 

 carbon appears to show, meanwhile, that the contraction at 

 D, before mentioned, consists of two moments, D 1 and D 2 , of 

 which the former embraces the interval of temperature from 

 705° to 725°, the latter the interval of temperature from 740° 

 to 800°. The corresponding division of the critical point D' 

 could, on the contrary, not be observed ; for this is required 

 the photographic reproduction of the changes of length. 



some approximate values of the coefficients of expansion K in steel and 

 soft iron during the interval of temperature from 0°-1000°. In steel he 

 has found K = 0-0000140, in soft iron K=00000145. 



That I got such a remarkably low value for K in soft iron doubtlessly 

 depends upon a masked contraction at D beyond the limits of that 

 observed. 



Phil. Mag. S. 5. Vol. 46. No, 279. Aug. 1898. P 



