330 Sir J. Dewar and Mr. R A. Hadfield. Effect of [Nov. 24, 



is comparatively brittle, even with low carbon. Upon exceeding 

 7 per cent, the material now known as "Era" manganese steel is 

 formed, and continues up to 17 or 18 per cent. Manganese steel 

 proper is the alloy containing 1115 per cent, of manganese with 

 carbon varying from 0'80 1'40 per cent. 



We will deal first with manganese steels having low carbon, i.e., under 

 0-30 per cent. Test No. 14 (C 0'08, Mn 3'50 per cent.), the usual rise 

 in tenacity and loss in ductility occurs at - 182 C., and on the 

 specimen being allowed to return to normal temperature it does not 

 appear to be injured in any way. Samples Nos. 15, 16, and 17 (Mn 

 varying from 5'40 15'28 per cent.), which are extremely brittle at 

 normal temperature, show very little modification at the low 

 temperature. 



Dealing now with alloys having higher percentages of carbon, several 

 specimens tested with Mn ranging from 2*23 to 11'53 per cent, with 

 carbon increasing proportionately from 0'41 1'66 per cent, showed 

 normal behaviour at low temperature. An interesting specimen 

 No. 26 (C 1-23, Mn 12'64 per cent.) was examined, representing a 

 normal " Hadfield's Era manganese steel." At normal temperature this 

 gave 56 tons tenacity, with the high elongation of 30 per cent., and 

 after immersion in liquid air showed a slight rise in tenacity, the elonga- 

 gation, however, falling to 2^ per cent., the low temperature thus 

 entirely de-toughening the material. This result is somewhat 

 unexpected, as it might have been anticipated that the great ductility 

 of this material at normal temperature would not have been interfered 

 with to any great extent at the low temperature. In the ordinary 

 treatment of Mn steel for toughening, the sudden drop in tempera- 

 ture is about 1000 C., and in the liquid air only 200 C. A repetition 

 test, No. 26A, gave a similar result, the tenacity at normal temperature 

 being 65 tons, with 40 per cent, elongation, while at - 182 C. the 

 ductility dropped to nil, the tenacity remaining the same, viz., 

 64 tons.* Similar specimens of this steel cooled down and allowed 

 to return to normal temperature again exhibited the usual extraordinary 

 toughness of the material, thus showing that the de-toughening or 

 embrittling action is only temporary, as with the Swedish charcoal iron 

 and ordinary steel specimens. 



It is certainly curious to find that a specimen of steel, which 

 only a few moments before would break in the easiest manner, 

 can again be bent double. This is produced by a change in tem- 

 perature conditions of about 200 C. These results also show that 

 manganese steel, notwithstanding its many peculiarities, in this 

 respect falls into line with and is subject to the same laws as iron 



* It is very extraordinary that the metal iron, no matter what its treatment, 

 never becomes so ductile as the treated and quenched manganese steel mainly 

 composed of iron with an original ductility of 40 per cent. 



