2002 Volume 88 Issue 11 Pages 763-770
Influence of B on the selective surface oxidation behavior of Mn during recrystallization annealing was investigated by glow discharged spectroscopy, secondary electron microscopy and auger electron spectroscopy, on the 0.4mass% Mn added ultra low carbon steel.
It is well known that both Mn and B are segregated on the surface due to the selective surface oxidation during the annealing in a reducing atmosphere. When the amount of B in the steel was 11ppm, a B-Mn compound oxide is considered to be in molten phase, because the melting point of the compound oxide is lowered than the annealing temperature. As a result, the compound oxide was in globular shape in annealing at 850°C, due to the effect of surface tension.
In case of B free steel, Mn was found on the grain-boundary as Mn oxide, because of preferable diffusion through grain-boundary after recrystallization annealing. In case of B added steel, B segregated precedingly before recrystallizing, both on the grain-boundary and in the grain. Mn segregated after recrystallizing, forming a B-Mn compound oxide in molten phase. Because the compound oxide is considered to coagulate and move on the steel surface during annealing, the oxide was eventually distributed both on the grain-boundary and in the grain.
The morphology of a B-Mn compound oxide changed diversely according to the amount of the B in steel. It is considered that the melting point and the chemical composition of the compund oxide influence the morphology of the selective surface oxide of the annealed B added steel.
