14 Lange, Some Remarkable Steel Crystals. 



films of the phosphide, thus clearly revealing the 

 formation produced under the above circumstances. 



The examination under the microscope of the micro- 

 structure of steel sections after polishing and etching, 

 supplies other links of evidence of crystallization in a 

 regular system. The microstructure of an unannealed 

 steel casting in this way shows a pattern suggestive of 

 trellis-work, the white (ferrite) lines forming angular 

 figures. On examining the case-hardened portion of a mild 

 steel bar, we shall find the excess of cementite showing 

 as a series of fine straight lines forming frequently 

 angles of 90 and 45 and occasionally angles of 60 degrees. 

 Sections of quenched carbon steels show the well-known 

 structure of martensite, which has the appearance of 

 being built up of a system of needles running parallel to 

 the sides of an isosceles triangle. On quenching a 

 saturated steel from a high temperature, we obtain a 

 structure of martensite and austenite exhibiting a most 

 marked geometrical pattern of bands crossing at angles 

 of 90 and 45 degrees. Stead has drawn attention to the 

 similarity between the structure of overheated steel and 

 that of un worked and untreated steel that has cooled 

 normally from the liquid state. 



The internal crystalline structure of iron and steel has 

 been the subject of a great amount of highly skilled 

 investigation in recent years. The early studies and 

 experiments of Tschernoff, Osmond, Sorby, Le Chatelier 

 and Brinell, paved the way for the later researches of 

 Stead, Roberts-Austen, Sauveur, Roozeboom, Arnold, 

 Martens, Heyn, Carpenter, and others that have lifted 

 the veil that once shrouded the complex phenomena of 

 iron and steel, and have brought their mysteries within the 

 scope of definite laws. 



