The production flowsheet for anchor steel CM690 is hot metal pretreatment-80 t BOF-LF-RH-200 mm x 200 mm billet casting-rolling to φ50 mm round bar process. The products analysis results show that during acid etching process the string cluster MnS and TiN inclusions with around banded rich carbon structure in steel CM690 (/% : 0. 29C

0. 21 Si

1. 58Mn

0. 017P

0. 012S

0. 017Ti) are corroded to form capillary crack defect

and the rich carbon bainite and pearlite also corroded gradually. With controlling RH end [ S

]

0.004% ~ 0.007%

decreasing [N

]

from original 55 x 10

-6

~ 70 x 10

-6

to 40 x 10

-6

~50 x 10

-6

decreasing liquid superheating extent from 25 ~ 40 ℃ to 25 ~ 35 °C

controlling casting speed 1. 3 m/min and increasing secondary cooling water ratio from 0. 35 L/kg

to 0. 40 L/kg

the capillary crack defects in steel products are basically eliminated.