252 SUMMARY OF CURRENT RESEARCHES RELATING TO 



containing about 4 • 2 p.c. carbon, is accepted as an austenite-graphite 

 eutectic. The author regards graphite once formed as taking no part in 

 subsequent changes, and explains the horizontal at 1000° as indicating 

 separation of cementite from austenite. Some very pure iron-carbon 

 alloys were prepared and treated in ways calculated to favour the supposed 

 formation of cementite from iron + graphite at 1000^. In each case 

 the alloy was found to contain more graphite than could be formed 

 during solidification, indicating that not only had cementite not been 

 formed from graphite in the cooling after solidification, but that 

 cementite had decomposed, yielding graphite. The author makes some 

 suggestions as to the constitution of austenite, martensite, and troostite. 

 Among the contributors to a lengthy and valuable discussion on this 

 paper were C. Benedicks, H. le Chatelier, H. M. Howe, Jiiptner von 

 Jonstorff, A. Stansfield, J. E. Stead, and F. Wiist. 



Heat Treatment of Steels containing* 5 and 0*8 p.c. Carbon.* 

 C. E. Corson has investigated the effect on structure and physical pro- 

 perties of (1) heating to varying temperatures followed by cooling at a 

 constant rate ; (2) heating to a given temperature followed by cooling 

 at varying rate ; (3) varying the finishing temperature in forging, and 

 also the rate of subsequent cooling. The author's results agree with the 

 generally accepted theories of heat treatment. 



Effect of Low Temperature on the Recovery of Steel from 

 Overstrain.! — It is known that steel recovers from overstrain at 

 ordinary temperatures, and that this recovery is hastened by raising the 

 temperature. E. J. McCaustland has shown that the effect of continued 

 low temperature (below 0" C.) on a piece of steel which has been stretched 

 sHghtly beyond the elastic limit, is to arrest completely the recovery of 

 its elastic properties. The author also studied the progress of recovery 

 at about 20" C., and at the temperature of a steam bath, in steel which 

 had been overstrained and then maintained at a low temperature for 

 some time. 



Structure of Metals. | — A report of a lecture by J. A. Ewing. 

 The crystal granules are regarded as built up of polarised molecules, 

 crystalline orientation depending on their polar quality. An explana- 

 tion of the phenomena of strain and fatigue, consistent with this theory 

 of the structure of the crystal, is given. 



Equilibrium and Solidification Structures of the Iron-Carbon 

 System. § — In this paper on the much-discussed iron-carbon system, 

 C Benedicks critically reviews at some length the experimental results 

 hitherto obfciined, and the theories founded on them. He considers 

 that it has been proved that cementite is endothermic and metastable, 

 and that the reaction, mixed crystals -j- graphite = cementite, cannot 

 occur. Roozeboom's equilibrium diagram is accordingly simplified by 

 the omission of the horizontal line at about 1000° C. Iron-graphite is 



* Journ. Iron and Steel Inst., Ixxi. (1906) pp. 603-7 (abstract). 



t Tom. cit., pp. 616-21 (abstract). 



X English Mechanic, Ixxxv. (1907) p. 58. 



§ Metallurgie, iii. (1906) pp. 393-5, 425-41, 466-76 (36 figs.). 



