Here ya' go Craig. 20X 3% Nitrol etched specimen of 2 Iron crolle.
The top is the edge of the barrel segment blown out at the time of the burst and the fracture is clearly ACROSS the crolle pattern; steel is grey-black, iron silver-white. The crack appears to be in the steel alternee, or possibly at an iron-steel interface.
The straight lines in the lower right are interesting. The metallurgist suggested that they are evidence of shear deformation at the time of the high pressure burst.
These straight lines of silica within the iron strip may have been acquired as part of the rod rolling and twisting process. It looks like one in the middle left originated in a globular silica inclusion
