Effect of Al content on r-value of boron-bearing Al-killed steel sheet

It has been demonstrated that boron had a beneficial effect on the mechanical properties of continuously annealed Al-killed steel sheets since boron improved the grain growthability by substituting larger BN for AlN. It has been reported that deep drawability of boron-bearing steels could be improved either by optimizing the B/N ratio between 1.0 and 1.5 in wt% or by reducing Al content. However, the effect of aluminum content on r-value in the boron-bearing steel sheets has not been well discussed yet. In this study, the effect of aluminum content on r-value and recrystallization texture formation was investigated for laboratory-melt boron-bearing low carbon Al-killed steel sheets. The r-value of continuously annealed boron-bearing M-killed steel increased with decreasing aluminum content under the same grain size. In the steels with lower aluminum (Al=0.005%) content, the carbide coarsening in hot-rolled sheet was more significant as compared to those with higher aluminum (Al=0.055%) content. The recrystallization temperature was lowered with decreasing aluminum content, and the development of <111>//ND components was accelerated while that of <110>//ND components was retarded. Since the increase in aluminum content accelerates AlN precipitation in hot-rolled sheets, boron might remain as in solution and segregate to grain boundaries. On the other hand, the reduction in aluminum content causes preferential precipitation of BN in hot-rolled sheets. The improvement of r-value by reducing aluminum content in B-bearing low carbon steels was caused by the development of <111>//ND components which was reduced by boron in solution.