It is generally deemed for structural steels that the resistance against brittle fracture in transverse direction to rolling (Y-direction) should be inferior to the one in rolling direction (X-direction), since the notch-impact values for Y-direction are usually fairly smaller than that for X-direction at higher temperature side of transition curves.
Experiments were made to see whether such expectation is correct or not, using two heats of structural high strength steel (60 kg/mm
2 class), one with no directionality and the other with marked directionality. The fracture and flow stress curves of those steels were investigated in both X and Y-directions, and compared with the results of V-notch charpy test. As the result of the examination, the following were concluded.
(1) Each shape of two fracture stress curves, cleavage and fibrous, was almost the same for both directions in two steels tested.
(2) It was found that the maximum energy absorbed in V-notdh charpy test (
2VE
max) was correlated with the flow stress curve of round bar, measured at higher temperature (80°C), through a parameter, σ
1ε
1+0.2 σ
2ε
2 (cf. Fig. 17). This value,
2VE
max, had no correlation with the cleavage fracture stress curve.
(3) It was revealed in another paper 4) that the fracture stress curves, especially the cleavage type one, were closely related to the brittle fracturing as shown in Figs. 19 and 20.
(4) Then it was proper to conclude, taking into account the considerations above, that the difference in
2VE
max induced by rolling, was of no significance as regards brittle fracturing, provided that the notch-impact values at lower temperature range and the fracture transition temperature were equal.
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