Effect of preliminary treatment on the structure and phase composition of Fe-Cr-Co-Cu-Nb alloys

Conclusions

• 1. The segregation of γ-phase is observed in the structure of Fe-33% Cr-20% Co-2% Cu alloys with Nb and Al additives at temperatures below 1150°C. Quenching in water from 1200 °C (30 min) tends to increase the average grain size to 200–400 μm; this lowers the plasticity of the alloys.

• 2. It is observed that highly coercive α → α₁ + α₂ decomposition in the Fe-33% Cr-20% Co-2% Cu alloy with Nb and Al additives does not occur at temperatures below 670°C. σ-phase is observed radiographically in the structure at 650–670°C and above.

• 3. Plastic deformation gives rise to the formation of σ-phase in Fe-33% Co-20% Co-2% Cu alloys with Nb and Al additives along the grain boundaries, on segregations of the Laves phase, and at degrees of deformation of more than 60% in slip bands during aging over a period of 30 min at 610°C and above.

• 4. Preliminary plastic deformation and repeated quenching tend to produce a structure with an average grain size d=30–60 μm in Fe-33% Cr-20% Co-2% Cu alloys with Nb and Al additives; this improves the alloy's plasticity; in this case, segregation of σ-phase can be eliminated in the process of preliminary aging.