Grain Growth in Dual-Phase Steel

Incomplete Recrystallization and Subsequent Microstructural Evolution during Intercritical Annealing in Cold-rolled Low Carbon Steels

“…16) Figure 5 represents the relationship between the cube or square of the subgrain radius inside a NR and the annealing time at 750°C. For the discussion of the grain growth mechanism, the following type of equation 16) has often been used, where r is the average radius of grains, r 0 is the initial radius, and k is the rate constant. The value n is reported to vary with the controlling mechanism of the grain growth.…”

“…The value n varies by controlling the mechanism of grain growth and it theoretically becomes nϭ3 if the grain growth is controlled by volume diffusion of alloying elements at the a and g interface. 16) It is also reported that subgrain growth during intercritical annealing is controlled by the volume diffusion of alloying elements such as Mn and Cr at the a and g interfaces. 12,20) In addition, a rate constant k in Eq.…”

“…(1) is approximated by Eq. (2) when Ostwald ripening of the second phase (or carbide) in steels is dominated by volume diffusion of alloying elements, 16) ....................... (2) where s is interface energy, V m is molar volume, D M is the volume diffusion coefficient of element M in the matrix, x M is the atomic fraction of element M in the matrix, and K M is a distribution coefficient of element M between the matrix and second phase. As summarized in Table 2, the value of k (ϳ2.8ϫ10…”

“…5(c), the kinetics of subgrain growth can be explained more likely by applying nϭ2 at a longer holding time of more than 1 000 s. It has been reported that the value n becomes nϭ2 if the growth is controlled by the migration of grain boundary in the single phase. 16) Hence, subgrain growth in third stage of annealing is probably controlled by the migration of grain boundary in the a phase. In summary, the present results suggest that incomplete recrystallization of a during intercritical annealing can be caused by the g phase at the recrystallization interfaces and subgrain boundaries in a NR .…”

Ferrite recrystallization and austenite formation at the early stage of annealing in cold-rolled low-carbon steels

“…In contrast, high-strength low-carbon steels used in the automobile industry are often annealed at the intercritical temperature (Garcia et al 2005;Hayami et al 1979;Goodman 1984;Takayama et al 1982;Toji et al 2011). During the intercritical annealing, recrystallization of α and formation of austenite (γ) can occur at the same time in low-carbon steels.…”