Behaviors of Delayed Failure in Ultra-High Strength 18%Ni Maraging Steels

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  • 18%Niマルエージング鋼のおくれ破壊挙動
  • 18パーセント Ni マルエージング コウ ノ オクレ ハカイ キョドウ

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Abstract

Behaviors of delayed failure in an air environment were investigated in ultra-high strength 18%Ni maraging steels. The slow crack growth velocity caused by delayed failure increases with aging time in an early stage of aging, and after reaching a maximum, it decreases inversely with aging time. The aging time for the slow crack growth velocity to reach a maximum becomes shorter with increasing aging temperature.<BR>The delayed failure does not occur in vacuum environment, and therefore, it is assumed that the delayed failure is controlled by diffusion associated with stress-induced migration of hydrogen produced by decomposition of water adsorbed by the surface of the steel. The slow crack growth velocity of the delayed failure depends on the catalistic action of steels changing by the aging condition which results in the decomposition of water.<BR>The aging time for the slow crack growth velocity to reach a maximum at a respective aging temperature is independent of the composition of the steels and only dependent on the aging temperature, but the slow crack growth velocity depends on the chemical composition of the steels. Co and Ti have a large effect on the slow crack growth velocity, but Mo has little effect.<BR>It is considered that the behavior of the delayed failure is controlled by the formation and decomposition of Ni3Ti(DO3) which probably promotes the decomposition of water.

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