The effects of rolling process and tempering temperature on microstructure and mechanical performance of experimental steel are studied. The results show that the yield ratio and elongation of the experimental steel are lower under noncontrolled rolling; under off-line tempering after controlled rolling, the tensile and yield strength decrease slightly with the increase in quenching temperature, the yield ratio decreases and the elongation increases; under the condition of controlled rolling, ultrafast cooling (UFC), and off-line tempering, the microstructure is fine martensite lath and a large number of fine precipitates, the steel has the highest strength and elongation. With the increase in tempering temperature, the tensile strength of the experimental steel decreases gradually, the elongation increases monotonously, the yield ratio and impact energy increase first, and then decrease. After comparison and analysis, it is found that the best performance can be obtained by direct online UFC after controlled rolling, and then tempering at 630 C, that is, tensile strength 908 MPa, yield strength 863 MPa, yield ratio 0.95, elongation 21.41%, and impact energy 94 J at À100 C.
The RH vacuum refining technology is a vitally powerful method of producing clean steel. The inner diameter of traditional circular snorkel is very difficult to be increased owing to the metallurgical refractory thickness around the snorkels and the limitation of the area under the vacuum chamber, limiting the increase in refining efficiency. In order to improve the refining efficiency of the RH reactor, a new designed RH degasser with an optimized arched snorkel is established. This design replaces the traditional two circular snorkels structure with the two arched snorkels and greatly enhances the cross-sectional area of snorkel. In this study, the flow characteristics of this new type RH were studied and analyzed by establishing a 1 : 5.5 physical model of RH with arched snorkels. Results show that the circulation flow rate of RH with arched snorkels can increase by 100% ∼ 180% and the mixing time approximately decreases by 35% compared with RH with circular snorkels under actual production conditions. The circulation flow rate of RH with arched snorkels continues to increase obviously when gas flow rate exceeds the saturated value of RH with circular snorkels. The RH with arched snorkels can increase the refining efficiency significantly and has important application prospect.
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