2011 年 62 巻 8 号 p. 403
The galvannealing behaviors of Ti-IF steel and P-added steel are affected by the application of sulfur before annealing. For this study of those effects, the amounts of sulfur on the steel surface were 5-500 mg/m2.
In each steel, application of 500 mg/m2 of sulfur increased the number of ζ crystals, which were densely and randomly distributed. Furthermore, the galvannealing rate of each steel was higher than in steels without sulfur application.
The ferrite grains of the annealed surface with 500 mg/m2 of sulfur were finer than those with less than 50 mg/m2 of sulfur. Moreover, small (Fe,Mn) S particles formed along the fine grain boundaries. The thickness of the area consisting of those fine grains, which were as large as 2 μm, was approximately 0.8 μm.
The (Fe,Mn) S particles were formed as the steel was annealed after application of sulfur on the surface. The recrystallized ferrite grains on the surface were fine because the particles suppressed the grain growth. In galvannealing of the steel, the fine ferrite grain boundaries are the outburst reaction sites: they increased galvannealing sites and raised the galvannealing rate. Results show that the galvannealing rates of steels with added Ti-IF and P were almost equal.