The Corner crack of Nb bearing steel HRB400NB 180 mm x 180 mm billet has been studied and analyzed.The results show that improper control of continuous casting cooling process

nitrogen content in molten steel and mold flux can easily lead to corner cracking of Nb bearing billet along grain boundary. With process improvement measures including decreasing the nitrogen content in liquid from original (67 ~ 98) x 10

-6

to (40 〜55) x 10

-6

adjusting the arc radius at the corner of mould from 8 mm to 12 mm

decreasing the cooling water quantity of the mould from 150 m

3

/h to 120 m

3

/h

decreasing the water ratio of the secondary cooling from 1. 35 L/kg to 1. I L/kg and adjusting the partitioning ratio of secondary cooling from 26： 48： 17

： 9 to 36： 34: 19: 11

adjusting the basicity of the mould flux from 0. 65 to 0. 82

the viscosity from 1.3 pa • s to 0. 69 pa • s

and adjusting the melting point of shielding slag from 1260 °C to 1150 °C. The defects of corner cracks on the surface of billet are effectively solved and the quality of the products is guaranteed.