極低炭素 11Ni 鋼における微視組織と低温靱性の関係

概要

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The effects of microstructures on low temperature toughness have been studied in the fine-grained extra low carbon 11Ni-1Mo-0.5Mn steel which has a very low sensitivity to temper embrittlement. Low temperature toughness was examined on the basis of the relation between yield strength and transition temperatures. The excellent low temperature toughness of this steel was mainly attributed to the inherent toughness of tempered martensite matrix. One kgf/mm^2 decrease in yield strength at room temperature of matrix lowered transition temperature by about 25K, which was the fairly large value as compared with the previously reported values in high tensile strength steels or 2.5 to 3Ni cryogenic steels. The fresh martensite increased transition temperature even if the amount was very small. The stability of retained austenite against plastic deformation was very poor contrary to the stability against sub-zero treatments. The effects of the retained austenite on low temperature toughness depended morphologically on its size and distribution. The retained austenite lowered transition temperature without the loss of yield strength when its thickness was less than 0.1μm and further it was isolated from each other. However, when the phase grew larger and coalesced together, it turned to be disadvantageous to low temperature toughness.
社団法人日本鉄鋼協会の論文
1982-05-01