Graded Series of Chrome Steels at Low Temperatures. 839 

 Table VI. (Fig. 7.) 

 20 per cent. (Jr. 



Thermal treatment 



Annealed at 900° 0. 



Quenched at 900° C. 







Temperature of test 



15° C. 



-190° C. 



15° C. 



-190° 0. 





H. 



I. 



I. 



I. 



I. 



10 



122 



106 



12 



12 



20 



413 



380 



25 



20 



40 



636 



625 



. 50 



42 



60 



700 



698 



110 



98 



100 



774 



782 



276 



258 



150 



820 



832 



404 



390 



curves are shown in figs. 5, 6, and 7. In the annealed con- 

 dition the saturation value o£ the intensity is lower in each 

 specimen than it was in the previous one, and the suscepti- 

 bility at —190° 0. is less at the beginning and greater at the 

 end of the range than at 15° C, the crossing occurring for 

 specimens IV., V., and VI. at points corresponding to field 

 values of 125, 95, and 65 c.G.s. units respectively. 



The permanent lowering of the magnetic quality due to 

 immersion in liquid air is seen in these specimens too, the 

 new room-teinperature curve lying slightly below the former 

 one for the whole range examined in the case of the speci- 

 mens containing 12 and 16 per cent, chromium, and till the 

 magnetizing force reaches a value of 90 C.G.s. units in the 

 case of the specimen containing 20 per cent. 



In the quenched condition the diminution of magnetic 

 quality with the increase in chrome content is very marked, 

 but otherwise the behaviour of these specimens is exactly 

 the same as that of the three specimens first examined, the 

 curve II' lying invariably below the curve II, and the curve 

 taken when the temperature of the specimen had risen again 

 to 15° C. exactly coinciding with II. For all the specimens, 

 the form of the curves shows that crossing will only take 

 place for very high values of the magnetizing force. 



Two of the hysteresis curves for the specimen containing 

 16 per cent, chromium are shown in fig. 9. These are the 

 curves taken at room-temperature in the annealed and in 

 the quenched conditions. The curves taken at —190° C. 

 are not shown as they follow almost exactly the lines of 

 those taken at 15° C, and lie for the greater part of the 

 range just outside them, the residual magnetism and 

 the coercive force both being slightly greater at — 190° 0, 



3K2 



