424 SUMMARY OF CURRENT RESEARCHES RELATING TO 



has observed straight lines, oriented in several directions, in the polished 

 surface, after etching with 2 p.c. nitric acid in alcohol. The lines were 

 considered to be Neumann lines. H. le Chatelier suggested that they 

 originated during polishing. When a grain of emery scratched the 

 surface in a direction identical with one of the cleavage planes of a 

 particular crystal, twinning occurred in that crystal along the track of 

 the scratch. Such lines would be interrupted where the scratch crossed 

 a crystal of different orientation. A twinned layer formed in this 

 fashion would be a Neumann lamella. The author has examined the 

 specimens after deep etching and considers that the results confirm the 

 truth of Le Chatelier 's suggestion. It was found that the lamellae were 

 in relief and were cubical in transverse section. 



A. Portevin and J. Durand * have found some exceptionally large 

 crystals in the outer layers of a decarburized rail. A polished and 

 etched section showed bundles of Neumann lines in the coarsely crystal- 

 line region. A very large crystal seen in the fracture, with one perfectly 

 plane face (a cleavage face) was cut out for examination. The cleavage 

 face was polished and deeply etched, and then showed very numerous 

 Neumann lines. Out of the six possible different planes in which 

 Neumann lamellae can occur in one crystal, according to Osmond and 

 Cartaud, five could be detected in the crystal examined. The authors 

 point out that the so-called Neumann lines described by Matweieff ( see 

 above) appeared to be oriented in at least eight planes in one crystal. 

 It is suggested that some of those lines were merely lines of cold- work 

 caused by scratching during polishing. By re-polishing after deep 

 etching it can be shown that Neumann lines are hollow grooves and are 

 not in relief. The authors doubt whether Neumann lamellae can be 

 produced by the action of emery in polishing, and point out that the 

 mode of preparation of Matweieff 's specimens — by breaking under the 

 hammer — is capable of developing a network of Neumann lamellae, 

 which are readily produced by mechanical shock. 



Volume Changes of Steel in Quenching.f — M. Oknof has deter- 

 mined the specific gravity of seventeen steels, containing ■ 08 to 1 • 67 p.c. 

 carbon, after various heat-treatments, such as quenching from different 

 temperatures. A number of the specimens were examined microscopic- 

 ally. Repeated quenchings of the hypereutectoid steels brought about 

 decomposition of the cementite and a consequent progressive increase in 

 volume, which masked the increase in volume due to hardening by 

 quenching. The temper carbon formed was visible in polished sections, 

 but not readily seen in the quenched specimens after etching, owing to 

 the dark colour of the martensite and troostite. In the same specimens, 

 after annealing, the temper carbon was readily visible within the pearlite ; 

 in some cases each mass of temper carbon was surrounded by a ferrite 

 envelope. 



Structure of Hardened Steel. J — H. Hanemann and E. H. Schulz 

 discuss the changes in volume and form which occur in the hardening of 



* Rev. Metallurgie, xi. (1914) pp. 771-9 (15 figs.). 



t Ferrum, xi. (1913-14) pp. 1-12 (13 figs.). 



t Stahl und Eisen, xxxiv. (1914) pp. 399-405, 450-7 (24 figs.). 



