Investigation of Precipitation Behaviors on Maraging Steels of Fe-18%Ni-Co-Mo-Ti Series by Measurement of Electrical Resistivity

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  • 電気抵抗測定によるFe-18%Ni-Co-Mo-Ti系マルエージング鋼の析出挙動の研究
  • デンキ テイコウ ソクテイ ニ ヨル Fe 18パーセント Ni Co Mo

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Abstract

Precipitation behaviors of 18%Ni maraging steels containing Ti were studied by measuring the electrical resistivity at liquid nitrogen temperature.<BR>On isochronal aging, Mo-rich zones which are significant precipitates in lower temperature aging, are formed following the precipitation of Ni3Ti(DO3) ordered phase at lower temperature region, and a metastable Ni3Mo phase is produced after the precipitation of Ni3Ti(DO24)η phase at higher temperature region.<BR>The presence of Co contributes not only to acceleration of the precipitation of Mo-rich zone, but also to promotion of the precipitation of Ni3Ti(DO3) ordered phase.<BR>On isothermal aging in the 18%Ni maraging steels with lower Ti content, decrease of the electrical resistivity is predominantly governed by the precipitation of Ni3Mo at temperatures over 753 K, but the 18%Ni maraging steels with higher Ti content always show the decrease of the electrical resistivity governed by the precipitation of Mo-rich zone at an early stage of the aging, even at 753 K and more, because the precipitation of Ni3Mo is retarded by presence of Ni3Ti(DO24)η phase.<BR>The activation energy for the precipitation reaction of Mo-rich zone increases with Ti content in the 18%Ni maraging steels. The activation energy in the steels without Ti is estimated at 150 kJ/mol by extrapolation from the relationship between the activation energy and Ti content, and the value is consistent with the data reported previously.<BR>It is presumed that the reason why the activation energy in the precipitation reaction of Mo-rich zone increases with Ti content is that precipitation sites of Mo-rich zone are occupied by the Ni3Ti(DO3) ordered phase produced prior to the precipitation of Mo-rich zone, and the Ni3Ti(DO3) precipitates form a potential barrier against the precipitation of Mo-rich zone.

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