Papers by Author: Hai Long Yi

Abstract: A Nb-Ti-Mo high strength steel was selected at two different cooling rates through ultra-fast cooling process, and its microstructures and strengthening mechanisms were analyzed. The results show the size of ferrite was decreased and the amount of bainite and micro-hardness were increased with increasing of cooling rate through thermal simulation. The UFC technology can improve the yield and tensile strength 25MPa and 35MPa, respectively, compared with conventional TMCP. The microstructure of this steel is mainly ferrite and good strength and toughness are caused by the refinement of ferrite and fine precipitates. Ultra-fast cooling technology improves the strength and toughness of this steel effectively.

Abstract: A Q550 high strength steel was selected at two different cooling rates through ultra-fast cooling process, and its microstructures and strengthening mechanisms were analyzed. The results show the bainite transformation temperature of the steel decreased with the increasing of cooling rate.The ultra-fast cooling process can improve the performance of Q550 compared with the conventional cooling process, and the yield strength, tensile strength and elongation are 600MPa, 755MPa and 19%, and - 20 °Cimpact energy is 253J, and good strength and toughness are obtained under ultra-fast cooling process. The microstructure of this steel is bainite and good strength and toughness are caused by the refinement of bainite and fine precipitates. Ultra-fast cooling technology improves the strength and toughness of this steel effectively.

Abstract: In recent years, the ultra-fast cooling process is a new technology used to control the strip cooling process in the international which corresponds to an average cooling rate higher than 150°C/s. This new technology can provide an effective means to the development of low-cost and high-performance steels. In this paper, the phase transformation temperatures, microstructures and mechanical properties of a Ti microalloyed steel were investigated by means of a themomechanical simulator and a D450mm mill equipped with ultra-fast cooling device. The results show that the phase transition temperatures decreased and micro-hardness increased with the increasing of cooling rate. The microstructures of steel used ultra-fast cooling process was small and more uniform than the ones used laminar flow cooling and air cooling process, and finer and uniformity dispersed precipitates can be produced under ultra-fast cooling process, hence higher yield strength and good elongation was obtained for the steel. The ultra-fast cooling technology has a good effect on the microstructures and properties of the Ti microalloyed steel.