船舶用低合金鋼の強度特性に及ぼすNiおよびCrの影響(<特集>海事研究の基盤としての研究施設)

概要

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The effect of Cr and Ni contents on the strength and the toughness of low alloy steels for large forgings for a ship was investigated. In the first step, the 14 materials of a fixed chemical composition except for Cr and Ni contents which were varied systematically in the range from 0.2 to 3% were prepared. The strength and the toughness of the steel depend on the bainitic lath size. Cr and Ni additions refine the bainitic microstructures by lowing bainite start temperature, and make the bainitic lath grains acicular. They improve the strength and the toughness of the material. Ni addition also makes the austenite grain size to become coarser, thus too much Ni addition leads the material brittle. It revealed that the highest toughness is obtained in the 1.6Cr-1.6Ni material. In the second step, the materials were treated in the heating process which simulates the manufacturing process for the large forgings. This process sometimes causes coarsening the grains. In this study, the most of materials reduce their toughness remarkably by the process. Only the charpy absorbed energy of 0.75Cr-3Ni material didn't decrease. It shows the high tensile stress of 1160 MPa and the high charpy absorbed energy of 61 J, could satisfy the target of the strength and the toughness, tensile stress > 1050MPa and charpy absorbed energy > 50J.
独立行政法人海上技術安全研究所の論文
2009-09-28