Fe-Ni-Coマルテンサイト合金の恒温時効硬化について

抄録

It has previously been reported that the age-hardening process of Fe-Ni-Co martensitic alloys takes place in two stages where the initial hardening occurs due to ordering and the second occurs due to strain hardening of matrix. In this paper, the second stage hardening of these alloys during isothermal ageing was investigated metallographically comparing with the behaviours of the age-hardenable Fe-Ni-Mn alloys which were already reported.
The results obtained in this paper are summarized as follows:
(1) The precipitation of the austenite from the martensitic matrix occurs more easily in the hardening stage of the Fe-Ni-Co alloys than that of the Fe-Ni-Mn alloys.
(2) The second stage hardening of Fe-Ni-Co alloys is accompanied with the increment of the lattice parameter of the martensitic matrix and of the amount of the precipitated austenite.
(3) From some considerations based on the measurements of the lattice parameters of the austenite, it seems that the concentration of solute atoms in the austenite is lowered as the ageing process advances, and also that the ferrite conjugated with the austenite separates changing its concentration of solute atoms in the matrix. The main reason for the second stage hardening seems to be due to strain hardening occurred by the precipitation of the ferrite above mentioned.
(4) The results of the measurements of the order-disorder transformation points of Fe-Ni-Co alloys suggest that (i) Ni atoms are substituted for Co atoms when Ni atoms are alloyed to the Fe-Co ordered structure, and (ii) the ordering energy parameter of the Fe-Ni bcc phase is greater than that of the Ni-Co bcc phase.
Comparing with the energy parameters of bcc phases of binary alloy systems, such as Fe-Ni, Fe-Co, Ni-Co, Fe-Mn and Ni-Mn, it is concluded that the separation of the martensitic matrix into the two bcc phases due to the miscibility gap island is possible in the Fe-Ni-Mn system but impossible in the Fe-Ni-Co system.