Abstract：The surface cracks of boron containing steel billet were observed by scanning electron microscope and metallographic analysis. Combined with the mechanism of cracks formation, the surface cracks of Wuhu Xinxing 10B21 boron containing steel billet were analyzed from three aspects: mold copper pipe, secondary cooling zone cooling and physical and chemical properties of mold slag. The results show that optimizing the material and taper of mold copper tube, adjusting the specific water content and distribution ratio in the secondary cooling zone and coordinating the lubrication and heat transfer effect of mold flux are conducive to reduce the surface crack defects of boron containing steel billets. The conducted production practices were as following. The total taper was reduced from 2.0%/m to 1.8%/m by changing the common hard Cr plating to Ni-Cr composite plating. The specific water volume in the secondary cooling zone was reduced from 0.6 L/kg to 0.5 L/kg, and the distribution ratio was adjusted from 34∶34∶20∶10∶2 to 31∶26∶20∶13∶10. The viscosity of mold flux decreased from 1.358 Pa·s to 1.169 Pa·s, and the alkalinity increased from 0.75 to 0.98. By applying the above measures, the surface crack rate of the final slab is reduced from 17.4% to 2.3%, the billet surfaces were smooth, the vibration marks were flat and regular, and the yield of rolled products was also increased from 86% to 95%.
2022, Vol. 41 
