0)1 the Microstructm'e of Hypo-eutectoid Steel. 273 



and also those large crudely-formed pearlite areas of Widmanstatten 

 structures in the head, which proved unable to maintain their 

 foi'mation under wheel action ; and so it becomes comparatively 

 simple to arrive at the cause of failure by deduction. 



MiCROSTRUCTURE OF NORMAL StEELS. 



The four concluding photographs serve to illustrate normal 

 crystal structures. The first one (iig. 14) shows an almost carbon- 

 less iron, and consequently only the dark tracery of the crystal 

 boundaries is to be seen, as practically no pearlite areas are present. 

 The dark spots are enclosures of FeO. The two specimens of more 

 highly carburized steels (figs. 15 and 16) are from material which 

 fulfilled all the specified conditions of testing. 



The last one (fig. 17) is from a hypo-eutectoid steel of different 

 composition and treatment, which I have recently perfected and 

 made on a commercial scale. As could be expected from the 

 uniformity of microstructure and the absence of enclosed 

 impurities this special steel possesses tenacity and elasticity con- 

 siderably in advance of the ordinary steels at present used. 



Note on the Microscopic Methods adopted in the Examination 



of Steel Specimens. 



Preparation, 



The sample for examination under the microscope is first lightly 

 rubbed on a very fine-cut file until perfectly level, and exhibiting 

 the lines of abrasion lying in one direction. Polishing then pro- 

 ceeds on commercial emery-papers until the previous file-marks 

 are entirely removed and replaced with the finer ones produced by 

 the emery ; which course is followed on each of the four succeeding 

 grades of specially-prepared French emery-papers. Considerable 

 care is required to prevent the transference of the coarser grains of 

 emery to the finer papers, and, if due care is not observed in this 

 respect, it is practically impossible to produce good specimens free 

 from scratches. The polishing is completed by placing the specimen 

 in contact with a cloth or chamois-leather covered disc, primed 

 with alumina or ferric oxide, and, as the disc is revolved at high 

 speed by suitable gearing, the specimen soon assumes a featureless 

 silvery appearance quite free from the minute scratches left by the 

 previous operations. 



The specimen is then washed to remove any traces of the 

 polishing medium, again washed in alcohol, and rapidly dried in 

 the hot-air blast. A little plasticine is then placed on the usual 



