220 SUMMARY OF CURRENT RESEARCHES RELATING TO 



constituent with an acicular structure. Raising the quenching tem- 

 perature results in the diminution and ultimate disappearance of the a 

 constituent, the alloy quenched from a sufficiently high temperature 

 consisting wholly of the acicular constituent. A. Portevin and G. Arnou 

 find that when such homogeneous quenched specimens are re-heated to 

 temperatures below the critical point, the a constituent separates out 

 along the planes which appear as needles in etched sections. In this 

 behaviour the copper-aluminium alloys differ from the iron-carbon alloys 

 (steel) with which they have many points of resemblance. 



Structure of Hardened Steel.* — H. Hanemann gives a detailed 

 description of the mode of formation and the structure of the various 

 constituents of hardened and re-heated steels. A series of excellent 

 photomicrographs illustrates the descriptions. Austenite is a solid solu- 

 tion of carbide in y-iron. In etched sections it appears as uniform areas 

 with a roughened texture, white to black, showing twinning, and having 

 rectilinear grain boundaries. Martensite is a solid solution of carbide 

 in ^-iron, and has an acicular structure, containing deep-lying needles 

 appearing dark or raised needles appearing light. Strictly speaking, 

 the term martensite should be restricted to the needles, but it is con- 

 venient and usual to describe an acicular area, including the ground 

 mass as well as the needles, as martensite. Definitions of hardenite, 

 osmondite, troostite, sorbite, and ledeburite are also given. 



Structure of Alloy Steels.f — F. Fettweis describes the micro- 

 structure of a number of steels containing large percentages of 

 chromium and tungsten, separately or together. Alcoholic solutions 

 of acids were useless as etching reagents ; copper-ammonium chloride 

 solution was good, and sulphurous acid was better still. The carbide 

 in the so-called carbide steels originates in a eutectic corresponding to 

 the ledeburite of iron-carbon alloys. High contents of chromium, or of 

 chromium and tungsten together, reduce the carbon content of tlie solid 

 solution which first separates from the melt to such an extent that the 

 '' ledeburite " eutectic is formed even when the total percentage of 

 carbon in the steel is low. 



Slag Inclusions in Steel. J— G. Mars gives photomicrographs show- 

 ing the inclusions found in small sample ingots of steel, made by the 

 acid and basic open hearth, basic Bessemer, crucible, and electric furnace 

 processes. The samples were taken from the bath at different stages 

 before the end of the process. 



F. Pacher§ discusses this subject at some length, and gives photo- 

 micrographs, some of which are of fractures which show the effects of 

 the presence of slag inclusions. 



* Stahl und Eisen, xxxii. (1912) pp. 1397-1404, 1490-4 (36 figs.). 

 t Stahl und Eisen, xxxii. (1912) pp. 1866-9 (36 figs.). 

 I Stahl und Eisen, xxxii. (1912) pp. 1557-63 (24 figs.). 

 § Stahl und Eisen, xxxii. (1912) pp. 1647-53 (17 figs.). 



