Abstract: Effect of annealing process on the microstructure uniformity of cold-rolled low-carbon steel plate for hot dip galvanizing was studied by simulated annealing experiment and industrial trial production. The causes of mixed grain microstructure in the steel were analyzed and the solution was developed. The results show that lower heating rate is the main reason for the mixed grain microstructure. With the increase of heating rate, the microstructure becomes finer and more uniform. At lower heating rate, both extending the soaking time and raise the annealing temperature aggravate the inhomogeneity of microstructure. Aiming at the problem of the mixed grain resulted from the rate decline during the galvanizing unit production and combined with the simulated annealing test results, it is found that lowering the annealing temperature can improve such mixed grain problem, and based on which the annealing process for the rate reducing production is formulated and applied to the actual production.

Key words: annealing process, hot dip galvanizing plate, mixed grain, heating rate