X-ray diffraction photograms from various fractures in mild steel arc welds were taken. The author considered about the problems of rupture in weld metals in the light of lattice distortions.
Main conclusions in this paper are as follows:
1. Weld metals made under constraints have lattice distortions in some measure, but these are not so large as to cause the K
α doublets to merge to continuous broad lines.
2. The surfaces of shrinkage cracks and the so-called "striated" fractures are not identical, but it is true that shrinkage cracks are apt to occur in the so-called "striated" structures.
3. Blued "striated" fractures, namely the surfaces of shrinkage cracks, have pretty large lattice distortions which cause the K. doublets to merge to continuous broad lines.
4. In the vicinity of shear fractures in tensile test specimens of all weld metais, which showed large elongation values, say 40% or more, there appears a pronounced preferred orientation as well as in forged mild steels.
5. The silvery-like portion in fisheyes is not a surface of shrinkage cracks at lower temperatures, but a brittle fracture by applied loads.
6. An X-ray diffraction photogram is an adequate measure for comparing the brittleness of weld metals. And the fractures in mild steel arc welds are to be classified as in Table 3 in accordance with lattice distortions, namely brittleness.
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