586 C. H. Mathewson — Metallographic Description 



severe, as shown by the more prominent lines of deformation 

 (wavy lines giving a erevassed appearance to the grain-frag- 

 ments). If the metal is worked only while the temperature 

 is at red heat and thereupon allowed to cool undisturbed 

 (rapidly), the same grain characteristics are observed except 

 for the absence of lines of deformation. The effect of this 

 treatment is shown in fig. 64, with diagram of position at the 

 left, fig. 63. In fig. 14, it is observed that the edge of the 

 chisel has been turned in use. This condition must have 

 influenced the structure somewhat at the extreme edge. Such 

 alteration does not, however, extend far from the edge. For 

 example, the position represented by fig. 56, is near enough 

 the. edge to show a fissure where the metal has split in use. 

 Yet there seems to be no interference with the normal elonga- 

 tion of the grains as prescribed by the original process of 

 hammering from the sides. 



It seems probable that more than one heat was used in 

 forging the blade of this chisel. This would explain the 

 uniform coarse grain of fig. 58, representing the condition of 

 the metal where the taper begins, and the fact that the grain 

 is more highly refined in this vicinity than along the body of 

 the object. According to this interpretation, the whole blade 

 was partly forged to shape in the first heat. On reheating 

 to the forging temperature, coarse grain developed and was 

 subsequently unaltered in this portion of the piece, but was 

 altered, as described above, further along towards the edge. 



The structure at the head of the chisel is shown in fig. 60, 

 with diagram of position at the left, fig. 59. This represents 

 the general structure in the body. It clearly indicates that the 

 object preserves approximately the shape of the original cast- 

 ing, since large unreerystallized fragments of the original 

 grains may still be seen. Owing to the use of high tempera- 

 tures in forging or annealing no traces of the internal grain 

 structure remain. The small dark spots represent particles of 

 sulphide. Normally a large part of this material separates out 

 between the casting grains, and in this photo-micrograph some 

 of it may still be seen in the grain boundaries. In completely 

 recrystallized structures the sulphide is distributed without 

 relation to the grain boundaries, e. g., fig. 69. The present 

 structure may have been developed by reheating after hot- 

 working or by annealing after cold-working. Since the blade 

 was almost certainly hot-worked, the former interpretation 

 seems more reasonable. 



