Graded Series of Chrome Steels at Low Temperatures. 833 



was then allowed to heat up to 15° C. again, and tested once 

 more to find whether the lowering o£ the temperature had 

 had any permanent effect upon its susceptibility or not. 

 In addition to the tests already mentioned, each specimen 

 was also tested both at 15° 0. and at —190° 0. for magnetic 

 hysteresis, and the effect of the lowered temperature upon 

 the residual magnetism and the coercive force noted. 



The next condition, condition 3, was attained by heating 

 the specimen to 900° C. and plunging it into water at 

 15° C. ; and with the specimen in that condition, exactly the 

 same series of tests was gone through as in the case of the 

 specimen in the annealed condition. Each complete test 

 was in every case carried out twice, and excellent agreement 

 was obtained between the two sets of results. 



One precaution that was carefully observed in the carrying 

 out of this work is to be specially noted. After every change 

 of temperature, and before a magnetic test was made at the 

 new temperature, the specimen was subjected to a process of 

 demagnetization by reversals which, the initial value of the 

 field being great and the final value zero, left it devoid of 

 magnetism and magnetic history. It is well known that 

 some such process must be applied to a specimen previous to 

 carrying out a magnetic test in order that it may be rendered 

 neutral ; but it is far from generally known that any thermal 

 treatment applied to a specimen between its neutralization 

 by the process of reversals and the following magnetic test, 

 renders it peculiarly susceptible to magnetism *, and that 

 therefore a specimen rendered neutral at one temperature 

 ceases to be neutral if the temperature is changed. Before 

 carrying out a magnetic test after a change of temperature 

 then, it is essential that the specimen should be submitted to 

 a process of reversals at the new temperature. 



Discussion of Results. 



Specimen I. (1 per cent. Cr.). — The first specimen tested 

 was a steel containing 1 per cent, chromium. The chief 

 results obtained are shown in Table I., and the corresponding 

 curves in fig. 2. The first set of results, corresponding to the 

 curve marked I, gives the readings for the I-H curve taken 

 with the specimen at room-temperature in the annealed 

 condition. The corresponding curve marked I 7 belongs to 

 the second set of results, and is the curve characteristic of 

 the annealed specimen at the temperature of liquid air. 



* "On Magnetic Testing," by J. G. Gray & A. D. Ross. Phil. Mag. 

 Jan. 1911. 



