( 947 ) 



XX. — On the Thermal Conductivity and Specific Heat of Manganese-Steel. 

 By A. Crichton Mitchell, B.Sc. 



(Read 1st April and 1st July 1889.) 



Introduction. 



Until a few years ago it was the general opinion among metallurgists that the 

 presence of manganese in steel exceeding the proportion of 1 per cent, is prejudicial to 

 the value of the steel, inasmuch as a higher percentage of manganese has the effect of 

 lowering markedly its tensile strength and toughness. But in 1884, Messrs Hadfield 

 & Company, of the Hecla Steel Works, Sheffield, exhibited, at a meeting of the Institute 

 of Mechanical Engineers, a number of samples of steel containing upwards of 10 to 15 per 

 cent, of manganese,"and submitted the results of experiments, which showed that the 

 samples were, in point of tensile strength and hardness, in no way inferior to steel. Again, in 

 1888, Mr R. A. Hadfield read to the Institute a paper on the subject, giving the details 

 of a large number of tests, which brought to light some interesting mechanical pro- 

 perties of alloys of manganese and iron. Since its introduction, these alloys (and 

 particularly that containing 10 to 15 per cent, of manganese, known as " manganese-steel ") 

 have been studied by several physicists, and further peculiarities have been found. It 

 appeared desirable that the thermal conductivity of so peculiar a substance should be 

 investigated. The present paper is an account of experiments made in the Physical 

 Laboratory, Edinburgh University, with a view to the determination of its thermal con- 

 ductivity. In the reduction of such experiments a knowledge of the specific heat is 

 necessary, hence there is also given an account of experiments whereby the specific heat 

 was determined. 



General Properties of Manganese-Steel. 



It will be well to give here a brief summary of the properties of this substance, so far 

 as they have as yet been investigated. In the first place, the peculiar effects of the 

 addition of varying percentages of manganese to steel must be noted. Mr Hadfield's 

 experiments on this point may be shortly summarised as follows : — Ordinary steel 

 contains from 0*6 per cent, to 0*8 per cent, of manganese, besides the usual pro- 

 portions of carbon, silicon, phosphorus, &c. If the proportion of manganese be increased 

 to 2 - 5 per cent, a marked falling off in tensile strength takes place, the material becoming 

 at the same time somewhat brittle and "unsound"; if from 2'5 to 7'5 per cent, be 

 present, the steel becomes exceedingly hard, the tensile strength is still lowered, and it 

 becomes so brittle that small samples may be reduced to powder in a mortar ; as the 

 proportion of manganese increases to 10 per cent, the brittleness disappears, and the 



VOL. XXXV. PART IV (NO. 20). 7 F 



