CHANGES IN STEEL OF CORE BARREL 



439 



steel. A cutting from the tip of the core barrel and, for comparison, a 

 cutting taken 2 feet higher up were submitted to the Bureau of Stand- 

 ards with the request that the temperature to which the tip was sub- 

 jected be determined as closely as possible. The report was accompanied 

 by two micrographs showing the difference in structure. These are re- 

 produced in figure 3. The conclusion reached is that "the structure at 

 the tij:) indicates that the metal was heated above the upper critical range 

 (900 degrees centigrade) and then cooled fairly rapidly (more rapidly 



Figure 3. — Micrographs of Steel from Core Barrel 



a, unhealed steel 2 feet from tip ; 6, heated steel tip. The change of structure is 

 due to the heating of the steel at tip to a temperature "as high as 1,050 degrees centi- 

 grade," followed by rapid cooling. 



than in air). The tip of the pipe was not heated long enough to produce 

 pronounced grain growth, which occurs in this type of steel after pro- 

 longed heating above 950 degrees centigrade. It was estimated, however, 

 that the temperature reached was as high as 1,050 degrees centigrade." "* 

 This independent evidence is in agreement with the conclusion reached 

 on an earlier page, that the temperature was in the neighborhood of 

 1,100 degrees centigrade. 



Production of Heat by Friction 



It is rather difficult to picture the conditions under which a steel, 

 heated to a temperature at which it can be forged, though not easily, 

 could nevertheless act as an abrasive in cutting rock. It is to be noted, 

 however, that on account of the good conductivity of the pipe only the 

 extreme tip was so heated, so that a tearing off of the softened end would 

 expose cooler and stronger steel for further cutting. As a matter of 

 fact, it is very doubtful whether any further cutting was accomplished 

 after this condition was reached. Probably the principal action at this 



^ Report from ilr. S. Epstein : U. S. Bureau of Standards. 



