Phase and structural transformations during heating of metals and alloys

Conclusions

• 1. We investigated the relationships between structural changes during heating of quenched metals and alloys, effect of impurities, carbon, and carbide-forming and noncarbide-forming elements on the temperature range of inheritance of the original substructure, and also the mechanism of recrystallization.

• 2. During recrystallization of quenched titanium and iron free of carbon (nitrogen) impurities no structural inheritance is apparent as after preliminary annealing. Secondary recrystallization occurs immediately after completion of the transformation.

• 3. Structural inheritance in originally quenched steels and alloys is due not to the displacement mechanism of rebuilding the lattice during the original treatment but to the barrier effect of second phase in the subboundaries and the clusters of foreign atoms accumulated there due to redistribution of alloying elements between the α and γ phases in the interphase temperature range.

• 4. An elevated heating rate, preventing development of diffusion processes (coalescence, solution of particles, redistribution of alloying elements, equalization of the composition of austenite) may lead to an increase or decrease of the temperature range of inheritance, depending on the chemical composition of the steel.

• 5. The heating rate has a large effect on local nucleation of austenite and the number of growing centers of recrystallization due to accumulation of local microstructural stresses or structural defects resulting from the difference in the expansion coefficients of ferrite and carbide.

• 6. The accumulation of microstructural stresses (defects) during thermal cycling of steels tempered at high temperature has the same effect on the place of nucleation and the number of growing austenite centers as the heating rate.