666 SUMMARY OF CURRENT RESEARCHES RELATING TO 



but the results were mainly negative. The particles thrown off into the 

 surrounding liquid by the "spark discharges were found to be very regular 

 minute spheres ; diameters measured ranged from 5 /x down to • -2 p-. 



Progress of Metallography 1909-1912.*— E. Heyn summarizes 

 critically the more important researches of the last three years, and adds 

 bibliographical references to 540 metallographical papers. The iron- 

 carbon system is considered at some length. 



Crystallization and Structure of slowly-cooled Steels.f— N. T. 

 Belaiew describes the processes of crystallization occurring in steel from 

 the beginning of solidification down to the lower limit of the critical 

 rangestand shows how the resulting structures are produced. The author's 

 views are based chiefly upon an examination of nine ingots containing 

 0-45-2 -30 p.c. carbon, made by melting pure iron with carbon in 

 crucibles, maintaining the melts in a fluid state for two hours and allow- 

 ing the crucibles and their contents to cool very slowly in the furnace. 

 " Damaskeened " steel is made by a similar process. Solidification in 

 steel proceeds by the formation of dendrites, and at the end of the solidi- 

 fication range the ingot may be regarded as a mass of interlaced den- 

 drites. The axes of the skeleton cry.stals, being the lines of primary 

 soHdification, tend to contain less carbon than the later solidifying 

 portions. For this reason, traces of the dendritic structure may persist 

 throughout subsequent treatments of the steel, and may be revealed by 

 long-continued etching with dilute acids. After complete solidification, 

 neighbouring particles tend to assume a uniform crystaUine orientation, 

 and the mass becomes an aggregate of approximately equiaxed crystal- 

 line grains of the solid sohition. In the next stage of crystallization, 

 ferrite, or cementite. according to the carbon content of the steel, sepa- 

 rates from the solid solution. This separation of " pro-eutectoid " takes 

 place wholly at the boundaries of the crystalline grains, if these are not 

 too large and the cooling is slow. The well known cellular or network 

 structure is thus produced. AYith more rapid separation the pro-eutec- 

 toid forms plates parallel to the faces of the octahedra, of which the 

 crystals of solid solution are composed : the resulting formation is the 

 Widmanstatten structure. 



A third structure occurring in isolated crystals and occasionally in 



castings is described. 



Formation of Osmondite in hypo-eutectoid Steels.J — J. Calian has 

 examined four steels containing 0-42, O'OS, 0-80, and 1*02 p.c. carbon. 

 A number of specimens of each were quenched from 900° C. and re- 

 heated respectively to 100°, 200% 300 , 400\ 500°, and 600° C. From 

 a microscopical study and a determination of solubility in dilute sul- 

 phuric acid, the author concludes that the transition constituent, osmon- 

 dite, is not formed only at one definite temperature, but may be formed 

 within the range ;-}0u° to 500° C. 



* Proc. lut. Assoc. Testing Materials, ii., No. 11 (1912) 58 pp. (8 figs.). Official 

 report to the Sixth Congress, New York, 1912. 



t Rev. Metallurgie, ix. (1912) pp. 321-42 (14 figs.). 

 I Rev. Metallurgie, ix. (1912) pp. 187-94 (22 figs.). 



