Effect of B on Growth of Recrystallized Grain of Ti-added Ultra-low Carbon Cold-rolled Steel Sheets

Abstract

The effect of boron (B) on the recrystallization behavior, in particular the growth of the recrystallized grain into the unrecrystallized grain, of titanium (Ti) added interstitial atom free (IF) steel sheets was studied from the viewpoint of the solute-drag effect considering the interaction between B and Ti atoms. The growth rate of the recrystallized grain at 5% fraction recrystallized decreased with increasing the B content. Furthermore, the decrease became more pronounced in the B added steels with the higher Ti content. The interaction energy between B and Ti atoms at the grain boundary was evaluated by the firstprinciples calculation in the bcc-Fe(111)Σ3[1 10] symmetrical tilt grain boundary. The attractive interaction between B and Ti atoms was obtained in most of the grain boundary atom sites examined. B segregation at the interface between recrystallized and unrecrystallized grains was concluded to induce Ti segregation through the attractive interaction between B and Ti atoms during interface migration. The mechanism for the suppression in the growth of the recrystallized grains was proposed to be caused by the decrease in the interface mobility caused by the enhanced Ti segregation.KEY WORDS: ultra-low carbon cold-rolled steel sheet; boron; titanium; recrystallization; grain growth; gain boundary segregation; interaction energy; first-principles calculation.recovery, nucleation of the recrystallized grain, and the growth of the recrystallized grain on Ti-added ULC coldrolled steel sheets (Ti-IF steel sheets) and found that each process is suppressed by B addition. 6) Furthermore, as steel contains more Ti, the recrystallization temperature is higher as a result of B addition, which suggests that not only B but Ti may take part in suppressing the growth of recrystallized grains.7) B addition increases the recrystallization temperature for Ti, Nb-added ULC cold-rolled steel sheets (Ti, Nb-IF steel sheets) as well and this trend is more obvious when the Nb content is higher. 8) Thus, to clarify the recrystallization suppression mechanism by B addition in ULC cold-rolled steel sheets, it is important to pay attention to the relationship between B and substitutional solute elements.In the present paper, we focused on the effect of B on the process of the growth of the recrystallized grain, in particular, among recrystallization elementary processes, that is to say, the process in which recrystallized grains grow into the deformed matrix, and discussed the mechanism for suppressing the growth of the recrystallized grain by B addition from the aspect of interaction between B and Ti atoms. 9) Experimental ProceduresTi-added ULC steels were vacuum-melted in an induction furnace and turned into 20 mm thick slabs by hot forging.

Advances in research on deformation and recrystallization for the development of high-functional steels

“…Moreover, it was confirmed that the amount of Ti segregation increases as the amount of B increases, which implies that B and Ti have a tendency to cosegregate. The co-segregation of B and Ti was also verified by the first principle calculation for the symmetrical tilt boundary of α-Fe(111)Σ3 ½1 10 [26]. The first principle calculation has also been conducted for the interaction between B and other substitutional transition metals in an α matrix.…”

“…However, it has been difficult to determine the actual state of the alloying elements in the moving interface. Recently, atom probe tomography (APT) has revealed the actual state of alloying elements in view of the solute drag effect using B bearing Ti-IF steel [25,26]. Figure 7 shows that .…”

“…Figure 7 shows that . Effect of B content on the growth rate of recrystallized grains at 5% fraction recrystallized in Ti-IF steels [26]. With permission of ISIJ.…”

“…With permission of ISIJ. Reproduced by permission from [26], copyright [2017, ISIJ]. simultaneous addition of Ti and B retards the velocity of the interface movement more effectively than the addition of Ti or B alone [26].…”

“…Reproduced by permission from [26], copyright [2017, ISIJ]. simultaneous addition of Ti and B retards the velocity of the interface movement more effectively than the addition of Ti or B alone [26]. Besides the fact that the simultaneous addition of Ti and B significantly suppresses the recovery and nucleation of recrystallization [26], it also retards the interface velocity of nuclei that grow into the deformed matrix.…”