Technology Development for Controlling Slab Transverse Corner Crack of Typical Micro-alloyed Steels

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A mathematical model for simulating the fluid flow, heat transfer and solidification in the conventional mold and the chamfer mold, together with a finite element stress-strain model in the straightening process of both molds, were established for the typical niobium, vanadium, and titanium micro-alloyed steels. On the basis of both numerical analysis, the mold copper plate with an optimum chamfered shape was designed and applied in industrial tests. The predicted results from numerical simulation of fluid flow, heat transfer and solidification in the conventional mold and the chamfer mold show that the increased chamfered angle leads to an approximately linear increase of the slab surface temperature, but it also causes strong flow near the slab corner. Very small chamfered length can lead to a significant increase of the temperature near the slab corner. However, with further increasing the chamfered length, the temperature of the slab corner increased slightly. The calculated results from the finite element analysis of stress-strain during the straightening process show that at the same slope width, the tangential strain on the slab edges and corners is minimum when the chamfered angle is 30° and 45°, which is only 40% to 46% of rectangular slabs with the same cross-section area. At the same chamfered angle of 30°, when the chamfered length is controlled between 65–85 mm, the tangential strain on the part of the slab edges and corners is relatively smaller. Industrial test results show that the slab corner temperature at straightening segment increases about 100 °C by using chamfer mold compared to the conventional molds. The slab transverse corner cracks have been reduced more than 95% in comparison with those in the conventional mold.