溶融亜鉛中における切欠き付綱板モデルの熱応力による液体金属ぜい化割れについて

概要

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It is well known that thermal stresses occur in steel structural members by rapid heat transfer from molten zinc, when they are hot dip zinc galvanized, and the residual deformation remains in them. If they have notches, the stress concentration can be induced. On the other hand, it was previously reported by the author that steel was markedly embrittled when coated with molten zinc and then deformed in tension. In this study, from the point of view of fracture mechanics, fracture toughness tests were carried out in molten zinc and the nominal fracture toughness K_i of SM50A steel was obtained using the notched 3 point bend specimens. By analyzing the nominal stress intensity factor at the slit tip of the notched rectangular SM50A steel plate immersed in molten zinc, the immersing speed of crack initiation was obtained. The result of the immersion tests on the notched rectangular plate coincided well with the above analysis. The results obtained are as follows : (1) nominal fracture toughness K_i in molten zinc of 16 mm thick SM50A steel plate with 0. 3 mm notch width was 100 kgf/mm^3/2. (2) Even if there exists the stress just below the crack initiating level in molten zinc, the delayed fracture hardly occurred within 10 min. (3) The maximum nominal stress intensity factor at the slit tip of the notched rectangular steel plate decreased with increasing immersing speed.
1981-02-15