bO Dr. J. Muir. On Changes in Elastic Properties [Aug. 11, 



" On Changes in Elastic Properties produced by the sudden 

 Cooling or ' Quenching ' of Metals." By James Muir, B.A., 

 D.Sc., late 1851 Exhibition Science Besearch Scholar. Com- 

 municated by Professor Ewing, F.B.S. Beceived August 11, 

 1902. 



(Being part of a Thesis submitted for the degree of Doctor of Science, Glasgow 



University.) 



It is well known that when steel is quenched from a red heat, its 

 elastic properties suffer a profound change, the material becoming 

 extremely hard and brittle. It is also known that quenched steel, 

 when tested under tension, exhibits no distinct yield-point, Hooke's 

 law is departed from quite gradually until abrupt fracture occurs at a 

 high stress. The effect produced on copper by quenching has been 

 considered, at least in some respects, the reverse of that produced in 

 steel. The experiments to be described in this paper, however, show 

 that with mild steel, soft iron, copper, zinc, aluminium, brass, and so 

 probably with all metals, quenching from high temperatures produces 

 effects which are analogous to one another; in all cases there is a 

 marked loss of elasticity produced by quenching, low loads producing 

 appreciable permanent extensions or " sets." 



The method of experimenting need not be described in detail here, 

 as it was identical with that described in the paper by the present 

 author on " The Tempering of Iron hardened by Overstrain."* The 

 new 5-ton testing machine of the Cambridge Engineering Laboratory 

 was however employed for many of the experiments in preference to 

 the large 50-ton gun machine previously used. Small strains of exten- 

 sion and of compression were measured by instruments of Professor 

 Ewing's design — extensions by means of the 4-inch extensometer 

 illustrated on p. 2, ' Phil. Trans.,' A, 1902, compressional strains by 

 the instrument illustrated on p. 79 of Professor Ewing's book on " The 

 Strength of Materials." The heating of the specimens was obtained 

 by means of the gas furnace used in the earlier experiments on temper- 

 ing after overstrain, temperatures being measured by a Callendar's 

 direct-reading platinum resistance pyrometer. The hot specimens 

 were " quenched " by plunging them vertically into a large tank of 

 cold water. 



The results to be recorded in this paper may be gathered from an 

 examination of the accompanying series of diagrams. The diagrams 

 give with one exception (Diagram 4) the results of tension tests, and 

 it need only be remarked that all the stress-strain curves have been 

 " sheared back" in the manner suggested by Professor E wing, and 



* ' Phil. Trans.,' A, 1902, p. 1. 



