OS2205 組織制御と表層軟化による高強度鋼の遅れ破壊感受性低減(OS22-3 水素と強度,OS-22 水素環境の材料強度特性への影響)

概要

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High strength steel with lower susceptibility of delayed fracture has been required to be developed, while, generally, steel above 1200 MPa of tensile strength increases the susceptibility. In the present study, the susceptibility of tempered martensitic steel with 1450 MPa is tried to reduce through higher-temperature tempering by adding Si and surface-softening , using induction heating. The strength of surface-softened steel is 1150 MPa at the surface, 1500 MPa at the center and 1450 MPa in the average. The susceptibility reduces by adding Si-content of 1.88 mass %. This is because the Si adding reduces carbide precipitations along prior γ grain boundaries, which is observed by TEM, and prevents intergranular fracture. In addition, the Si adding reduces stress relaxation, i.e. stabilizes dislocation structure. Furthermore, the surface-softening enables us to reduce the susceptibility, since the hydrogen concentration at the surface of crack initiation is lower than that at the center.
一般社団法人日本機械学会の論文
2011-07-16