Abstract
It has been reported that an addition of boron increases total elongation of continuously annealed Al-killed steel sheet and that the addition of boron is sometimes utilized for improving the formability. The purpose of this study is to investigate the influence of boron content on workhardening behavior of Al-killed steel sheet.
Stress-train curves of low carbon steel depended on annealing temperature, over-aging temperature and boron content. In low boron steel, the low temperature annealing and low temperature over-aging resulted in the increase of the stress required to continue the plastic deformation in tensile test since the low temperature annealing and over-aging promoted the grain refinement and the fine carbide precipitation in matrix, respectively.
In high boron steel, on the other hand, there were no influences of both the annealing temperature and over-aging temperature on the stress-train curves. The independence of the annealing temperature and over-aging temperature may be attributed to strengthening of ferrite grain boundary and the fine carbides in matrix which were promoted by the large amount of boron, respectively.
The n-value of low boron steel increased significantly and showed a peak at lower strain. On contrast, the n-value of high boron steel increased slightly at lower strains and did not show a peak. In high boron steel, dynamic recovery would be activated more remarkably than in low boron steel since dislocation density in the early plastic deformation region in the tensile test may become higher by ferrite grain boundary strengthening which is due to boron segregation.
