PHYSICS. 365 



Howe, Henry M., Bedford Hills, New York. Research Associate in Metal- 

 lurgy. (For previous reports see Year Books Nos. 6-17.) 



I began at my owti laboratory a systematic search for the kind of 

 steel most suitable for helmets and body armor, at the request of the 

 Ordnance Department, of which I became a civihan expert. For this 

 I devised apparatus for accurate ballistic testing, with normal impact, 

 of the spherical surfaces of which the front and rear of helmets consist. 

 Later this w^ork was taken over and finished by Mr. W. J. Wrighton. 

 The Ordnance Department has authorized the publication of our results. 



I have studied the nature and causes of the peculiar w^hite coarse- 

 grained spots called "snowflakes" which occur in the otherwise fine- 

 grained fractures of the test pieces of certain alloy steels. I find that 

 they represent internal fissures made at a time when the structure of 

 the metal itself was coarse-grained like these spots. The fact that, even 

 when they represent as much as one-fourth of the sectional area of the 

 test-piece, they cause no appreciable lowering of the elastic limit, I 

 explain as meaning that the stretch w^hich occurs on passing the lowered 

 elastic limit of the cross-section w^here thus reduced by the fissure, 

 being confined strictly to this cross-section, is too minute to be detected 

 by any extensometer. Instead, the elastic limit actually observed is 

 that of the unfissured remainder of the test-piece when enough stretch 

 has occurred at innumerable points along its length to add up to a 

 measurable quantity. This general line of thought is due to Professor 

 H. F. Moore. 



With Mr. R. C. Groesbeck I have studied the four following sub- 

 jects, chiefly at the U. S. Bureau of Standards: 



(1) The influence of the conditions of casting on the position of the 

 internal contraction ca\'ity or pipe in solidifying masses. The experi- 

 ments were made with ingots of paraffin. 



(2) The influence of the severity of reduction in the individual 

 passes in rolling metals on the residual internal stresses. We rolled 

 steel strips in pairs, one strip superposed on the other, and measured 

 the degree by which these strips became bent, for given total reductions, 

 when this reduction w^as brought about by a few severe reductions, by 

 many light ones, and by an intermediate number of reductions of 

 moderate severity. The deflection increases with the severity of the 

 reduction per pass. This is referred to the greater skin friction between 

 the rolls and the piece rolled, which lessens the backward flow of the 

 surface metal, thus causing a correspondingly greater proportion of 

 the flow^ to occur in the deeper-seated layers. 



(3) The influence of phosphorus on the microstructure and hardness 

 of carbon steel after various thermal treatments. For this w^e used the 

 important series of steels varying greatly in their phosphorus content, 

 but otherwise alike, prepared by Mr. J. S. linger for another purpose. 



(4) The influence of thermal treatment on the microstructure of 

 pure carbon steels of various carbon contents. 



