超強力マルエージ鋼の破壊靱性の結晶粒径依存性

概要

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The effect of prior austenite grain size on fracture toughness (K_<Ic>) in 2750MPa grade 13Ni-15Co-10Mo maraging steel has been investigated. The prior austenite grain size was varied in the range of 7∿600μ using both thermomechanical treatment and solution treatment. K_<Ic> increased with increasing the grain size. For example, K_<Ic> increased from 20MPa・m^<1/2> for 8μ to 30MPa・m^<1/2> for 500μ and varied linearly with the reciprocal square root of the grain size. The acoustic emission measurement during fracture toughness test and fracture surface observation at the tip of fatigue precrack revealed that subcritical crack growth of intergranular fracture mode occurred as the grain size increased and K_<Ic> was apparently increased due to the microbranching effect of the crack front. On the basis of the above observation, it was suggested that true grain size dependence of K_<Ic> in 13Ni-15Co-10Mo steel might be less than the experimentally obtained result.
1983-01-01