190 M. Gr. E. Svedelius on the Changes in the Length and 



Approximate values of the coefficients of expansion in hardened 

 Steel during the interval of temperature from 0°-800°. Situation 

 of the critical re-tempering points of hardened Steel. In 

 6.g. 19 the length and temperature curves are graphically 

 reproduced from a steel rod of Sandviken wire containing 

 1*0 per cent, of carbon which was hardened in cold water 

 after having been heated to a bright red heat. The changes 

 of length of the rod, as calculated from these curves, are 

 given in the table below : — 



Table VI. — Sandviken Wire, 1*0 per cent. C, hardened. 





Change of Length during 

 Heating. 



Change of Length during 

 Cooling. 



o o 



0-100 



0-00120 0-00120 





100-200 



000160-0-00120=0-00040 





200-300 



0-00250-0-00160=000090 



0-00050 + 0-00070 = 0-00120 



300-400 



0-00340 - 0-00250 = 0-00090 



0-00170-0-00050=0-00120 



400-500 



0-00435 -000340= 0-00095 



0-00300 -0-00170 =0-00130 



500-600 



000580 - 000435 = 000145 



0-00455 - 0-00300 = 000155 



600-700 



000730-000580=000150 



000610 - 000455 = 000155 



700-800 



000895-0-00730=0-00165 



000835-0-00610=0-00225 



This table shows : — 



(xiii.) That the coefficient of expansion of hardened steel is 

 considerably smaller than that of annealed steel during the 

 interval of temperature from 100°-500°. The coefficient of 

 expansion of hardened steel has its least value during the 

 interval of temperature from 100° to 200°. 



The magnitude and situation of the anomalous changes of 

 length in the hardened steel rod, as ascertained from the 

 curves in fig. 19, are given in the following table: — 



Table VII. — Sandviken Wire, 1*0 per cent. C, hardened. 





d v 



d 2 . 



D. 



D'. 



Expansion to points named. 



Magnitude of contraction 1 

 or expansion at ditto J 



Temperature of ditto 



Time of ditto 



000160 



0-00008 



160° -200° 

 3 sec. 



000325 



400° -440° 

 2 sec. 



0-00732 



0-00055 



720°-740° 

 16*5 sec. 



000060 



670° -675° 



7 sec. 





Tables VIII, and IX. give an idea of the process of con- 



