Magnetic Pcrmeabiliiy of various Alloys of Iron. 



Ill 



the reversal back to softness by increasing the percentage of nickel, was most 

 unexpected. Upon jDutting another set of specimens to mechanical tests for tensile 

 strength and resistance to compression, similar changes in the mechanical pro- 

 perties were observed at nearly corresponding percentages. The following curves 

 illustrate this remarkable behaviour. In fig. 9 the coercive force in C. G. S. units 

 of these nickel-steels is plotted, the abscissae being percentages of nickel, and the 

 ordinates coercive force x 2. This curve shows the relative magnetic hardness of 

 these alloys ; the relative magnetic softness is shown by the reciprocals of the 

 coercive force, which are also plotted on the same figure. In fig. 10 the 

 tensile strength in tons per sq. inch is shown, the abscissae being as in fig. 9, and 



0^ 



§ 20 



y 





Fig. 9. 



the ordinates the breaking stress in tons per sq. inch. Again in fig. 11 the reduc- 

 tion in length per cent, produced by a compression load of 100 tons per sq. inch 

 is shown, the ordinates in this case being the percentage reduction.* 



This latter curve illustrates the mechanical softness of these alloys, and will be 

 seen to be very similar to that of the magnetic softness on fig. 9, whereas the curve 

 on fig. 10, showing the tenacity, resembles the magnetic hardness shown on fig. 9. 



* See paper on Nickel Steels, by R. A. Hadfield, Proe. Institute of Civil Engineers, March, 1899. 



