As has been stated in the 1st report, for a high tensile structural steel with tensile strength over 60kg/mm
2, the Si+Mn+V+Ti type i.e. the so-called Vanity type shows better weldability. However, as it has not been examined through satisfactory weldability tests, the final type of steel could not be established. In this report, with the object of improving Vanity type, the Vanity+Ni+Cr, the Vanity+Ni+Mo and the Vanity+Ni+Cr+Mo types were studied for as rolled and normalized conditions by various kinds of mechanical and weldability tests. The results obtained are as follows :
1. For as rolled condition, all kinds of steels show too high tensile strength, but good elongation and weldability are not warranted.
2. As for normalizing materiale, elongation is improved, but tensile strength becomes generally below 60kg/mm
2. The Vanity+Ni+Cr+Mo type is comparatively better and also recommended in point of weldability.
3. Large content of Cr seems to have bad effect on crack sensitivity of the material.
4. From the view-point of hardenability of the material it is recommended that the Dearden and O'Neill's equivalent carbon should be below 0.45.
5. On Kommerel test of crack is quaranteed by the I.I.W. maximum hardness below 350Hv and no breaking at the bending angle of 120 degree is also guaranteed unless the I. I. W. maximum hardness plus the hardness of parent metal exceeds 490Hv.
6. On kinzel test of normarized materials, larger lateral contraction below the notch is guaranteed by the I.I.W. maximum hardness below 350Hv.
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