Studies on hot rolled galvanized steel sheets: Effect of reheating on galvanizing

Galvanized hot rolled steel sheets are inferior to cold rolled sheets because of the segregation of carbides at the surface/sub-surface region. In order to change the distribution of the carbides at the surface/sub-surface region, continuous annealing/reheating operation is carried out at different temperatures prior to the galvanizing operation. The reheating temperature maintained in continuous annealing line is the main factor which redistributes the carbides at the surface/sub-surface region. At intercritical annealing temperature all the carbides get dissolved into the matrix and the surface became suitable for galvanizing reaction. The reducing atmosphere also plays an important role to remove all the room temperature oxides present at the surface. Thus, a combination of proper temperature and reducing atmosphere leads to the proper galvanizing on the hot rolled steel surface.