鋼溶接熱影響部靱性に果たす局部的硬化部まわりの応力・ひずみ特性の役割

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Two-dimensional FE-analysis has been conducted to investigate the stress-strain fields in the vicinity of M-A constituents corresponding to local hard zones (LHZ) in the weld HAZ. Existence of the LHZ elevates considerably the stress in the LHZ and causes very inhomogeneous deformation around the LHZ. Stress distribution in the LHZ is strongly affected by the shape of the LHZ : In the slender LHZ almost all region in the LHZ is exposed to elevated stress, whereas in the blocky LHZ only the edge region sustains high stress. The increase in the strength of the LHZ results in remarkable elevation of the stress level in the LHZ. This implies that the slender LHZ is cracked at a lower load level than the blocky LHZ, and that the crack nucleation in the LHZ is promoted by increasing the strength of the LHZ. The shape of the LHZ affects also the plastic deformation in the vicinity of the LHZ : Slender LHZ encourages the accumlation of plastic strain in the matrix region adjacent to the LHZ. Significant difference in deformation of the matrix and the LHZ will induce the fracture along the LHZ/matrix boundary. These analytical results suggest that the heterogeneous material including slender LHZ has lower fracture resistance than that with blocky LHZ. This finding was confirmed by the HAZ-notched CTOD test on high strength steel welds : The coarse grained HAZ including elongated M-A constituents fractured at an apparently lower critical CTOD value than that with massive one. Accordingly, it is necessary to control the shape of M-A constituents for toughness improvement of the weld HAZ.
社団法人日本船舶海洋工学会の論文

鋼溶接熱影響部靱性に果たす局部的硬化部まわりの応力・ひずみ特性の役割

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