EFFECT OF HOT DIP PROCESS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Ti-IF STEEL SKIN-PASSED GALVANIZED SHEET

Effect of hot dip process on the microstructure and mechanical properties of Ti-IF steel skin-passed galvanized sheet are studied on a continuous hot dip galvanizing line. The results show that the ferrite grain has a size of No.10 when the sheet temperature in RTH is below 830℃ and then coarsens gradually as sheet temperature increasing. As a result, the annealing texture of hot dip galvanized sheet changes from mainly {332}and {114}, when the ferrite grain is fine, to the typical {111} as the grain growth, accompanying with the increase of intensity, therefore the r-value increases. However, the r-value will decrease dramatically as the result of randomly distribution of texture when the sheet temperature in RTH exceeds 900℃. Skin-passing reduction has evidently effect on the mechanical properties of final products of Ti-IF steel skin-passed galvanized sheet. As the skin-passing reduction increasing, the yield strength increases obviously, the n-value decreases markedly, and the elongation decreases, but the tensile strength almost remains unchanged. In addition, its effect depends on the ferrite grain size of the final products. The coarser the ferrite grain is, the bigger the effect becomes. Therefore, r-value and n-value are contradictory to each other for skin-passed hot-dip galvanized Ti-IF sheets, and they should be balanced during planning hot-dip processes according to the application demand of customers.