Hot Dip Galvanizing Process On The Microstructure And Properties Of Dual Phase Steel

Dual-phase steel, which has many special properties such as high initial work-hardening rate, low yield ratio and good bake-hardening property, is widely used as auto components. And it is significant for auto-body lightening.Currently, dual-phase steel, in our country, is prejudicious for hot galvanizing coatings and welding process because of its high Si content. In this paper, based on cold rolling steel with low carbon and low Si, the effects of Cr, Mo on cold rolling dual-phase steels are studied. The differences in microstructure and properties of cold rolling dual-phase steel under different hot galvanizing temperature are analyzed. And the effects of Cr, Mo on dual-phase steels treated by simulating hot galvanizing and simulating bake process are analyzed. At last, the effects of Cr, Mo, Si, Nb on the texture of dual-phase steel are studied. The conclusions are as follows.Dual-phase steel with good comprehensive performances is gained under the condition that it is heated to 740℃, quenched. The comprehensive performances of dual-phase steel of C-Mn-Cr, C-Mn-Mo are better than that of C-Mn dual-phase steel. Mo can refine the ferrite grain, and Cr can cluster the interstitial atoms.Treating by hot galvanizing, the tensile curvea of dual-phase steel show obvious yield phenomenon, high yield strength, high yield ratio, high yield elongation. Dual-phase steel, added the elements of Cr, Mo, has higher yield strength, higher tensile strength, higher percentage of elongation and lower yield ratio than that of C-Mn dual-phase steel. These three kinds of dual-phase steel have good bake-hardening property, with BH value higher than 40MPa, and the BH value of dual-phase steel, which contains Cr, Mo, is more than 50MPa.After different heat treatments, the textures, gained by 650℃,740℃and 880℃heat treatment, change from a orientation toγorientation. Annealing treatments don't change the type of texture, but affect the texture'strength, especially strengthen the texture of {111}<110>. Alloy elements don't change the type of texture either, but the affect the texture's strength. After dual-phase treatment at 740℃, we find the volume fraction of{111} texture is increased by Si,{100} texture is decreased by Cr, Mo, and the texture of Goss is increased by Nb.