No abstract

Based on a basic water cooling model, a novel model with closed feedback loop was developed for online temperature control system (OTCS) to control the strand surface temperature online during steel continuous casting process. The OTCS considered the temperature delay to the casting speed and water flowrate and combined the feedback control model with feed forward control model for the control of secondary cooling water. The online feed forward control with the temperature of molten steel in the tundish and the temperature of cooling water was also considered. A fine adjusting temperature region and an optimal temperature region were applied to the OTCS to avoid big temperature fluctuation during control process and to shorten the adjusting time. A single point OTCS was applied to a slab continuous caster, showing that the slab surface temperature was well stabilised at the target temperature under the control of the OTCS in continuous casting process. During tundish change or big variation of casting speed, the low slab surface temperature could be quickly controlled to the target temperature again by the OTCS within 7 min. The industrial application indicated that the OTCS could reduce the slab surface cracks and aid in increasing productive efficiency in continuous casting.

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A novel method for the grain refinement of as cast Mg-1?8Mn alloy by simultaneous addition of trace Er and Al was developed. A series of Mg-Mn alloys with systematic additions of Er alone (Er) or simultaneously with Al (Er/Al) were designed in order to illustrate the effects of Er/Al on the microstructure of the Mg-Mn alloy. The results showed that significant grain refinement was obtained by simultaneous addition of Er/Al. The grain size decreased remarkably from over 800 mm in the unrefined alloy to 150 mm with the addition of 0?4 wt-%Er/Al. Adding Er alone to the Mg-Mn alloy did not evidently influence the grain size. The Al 3 Er phase was identified to be the dominant phase in the Er and Al containing alloys, besides elemental Mn particles. Based on the calculation of the planar disregistry between Al 3 Er and a-Mg, Al 3 Er particles could act as efficient heterogeneous nuclei of primary a-Mg during the solidification of Mg-Mn alloy.