14Ni-5∼15Co-5Moおよび14Ni-5∼7.5Co-7∼10Mo系マルエージ鋼の析出

Abstract

Precipitation in 14Ni-5∼15Co-5Mo, 14Ni-7.5Co-7Mo and 14Ni-5Co-10Mo maraging steels has been investigated as a function of cobalt or molybdenum content by measuring the change in electrical resistivity at liquid nitrogen temperature. Age-hardning has also been measured in some of the maraging steels, and the relation between tensile strength and resistivity decrease has been investigated.The results can be interpreted satisfactorily in terms of two precipitation stages. The precipitates formed in a low temperature region and in a high temperature region are named as the phase-L and the phase-H, respectively. In the low temperature region, the phase-L is precipitated in the early stage of isothermal aging and is gradually converted into the phase-H with the lapse of aging time. In the high temperature region, it is considered that the phase-H is precipitated from a solid solution without the precipitation of the phase-L. The temperature where the phase-L is precipitated in the early stage increases with increasing cobalt or molybdenum content. The line of demarcation between the precipitation of the phase-L and that of the phase-H is determined as a function of cobalt content in 14Ni-5∼15Co-5Mo maraging steels.