Papers by Author: Zi Yong Hou

Abstract: In this paper, common continous annealing (CCA) and ultra-fast annealing (UFA) were carried out on a cold-rolled interstitial-free (IF) steel, respectively. The microstructure of the annealed IF steel was characterized by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The mechanical property was examined using tensile test. The optimum annealing process parameters were then obtained. The results showed that, the recrystallization occurs at the temperature in the range of 780-830°C. The fraction of equiaxed grain increases with the annealing temperature increasing. The well combination of mechanical properties and formability was obtained when the IF steel annealed at 820°C, which was the result of the fine dispersed second phase particles. {001} texture was absent in the whole thickness of all the annealed IF steels. In addition, the strongest γ texture was found, and this was a potential way to improve the deep drawability of annealed steel sheets.

Abstract: Effect of coil temperature on the texture and microstructure evolution during cold rolling and annealing were investigated by OM, ODF and EBSD. The results indicate that the {223}<110> and {114}<110> textures appeared after cold rolling are inherited followed by annealing, whose intensities would be higher as the coil temperature decreased. Lower coil temperature could improve the uniformity of grain size and increase the fraction of low-angel grain boundaries as well as coincidence site lattice boundaries. And the {111}//ND texture is improved in the lower coil temperature cold and annealing steel sheet, which is beneficial for the deep-drawability.

Abstract: The effects of annealing routes (batch annealing and continuous annealing) on the development of microstructure and texture in a cold-rolled Nb-IF high strength steel sheet were studied by means of optical microscopy(OM), electron backscattered diffraction(EBSD) and ODF analysis. The results show that the finer and more homogenous recrystallization grain can be observed in the CA steel. The CA process leads to an increase in the intensity of the γ-fibers, and the very sharp and uniform γ-fibers are found in this case, which is beneficial to the deep-drawability.

Abstract: Good combination of high strength and high toughness has been considered as a critical factor of ultra-high strength steel plates. In this paper, a novel high strength steel plate of HSLA type containing Cu with 910MPa yield strength and 1163MPa tensile strength has been developed using an advanced TMCP (thermo-mechanical control processing) technology. The steel plates provide excellent combination of high strength, toughness and deformability. Microstructural evolution and mechanical properties of this steel during hot-working have been investigated. It is demonstrated that, at the relatively higher finish rolling temperature and cooling rate, the microstructure consists of acicular and granular bainite structures and a small amount of low bainite /martensite whose lath width is approximately 200~300nm. For the as-rolled conditions, despite the high strength and so low yield ratio, impact energy about 154J and fully ductility fracture at -90°C can still be obtained as documented for as-hot rolled plates.