The casting slab corner transverse cracks of steel Q550D (/% ： 0.15C

0.25Si

1.40Mn

≤0.010P

≤0.002S

0.03Nb

0.06V

0.015Ti

0.020Alt) have been analyzed to get the comer transverse cracks form in mold and further develop at secondary cooling area

besides at bending part ( Ⅲ brittle zone) of slab

the tensile-stress action of outer face of slab is also an important factor for corner cracking. With the process measures including decreasing water flow rate of width face of mold by 200 L/min and of narrow face by 20 L/min

improving precision of arc each other from ±0.5 mm to ±0.3 mm

improving the amplitude and vibration frequency respectively from 4~5 mm and 130~136 opm to 3.6~4.5 mm and 140~146 opm

increasing the mold taper from 0.9

%~1.0% to 1.0%~1.1%

improving edge natural cooling at secondary section to nozzle cooling

and decreasing nitrogen content in steel from ≤60 x 10

-6

to ≤40 x 10

-6

the occurring rate of comer cracks markedly decreases.