The metallurgical flowsheet of 230 nun casting slab of 700 MPa Ti microalloying low carbon steel is KR metal pre-desulphurization-210 t BOF-LF-RH-CC process. It is found that the median position of cross section of slab in laid up is breaking. The results by analysis on casting slab composition

structure

gas content

inclusions and hot plasticity show that the composition of median position is same as that in other part of slab (/% : 0.075 ~ 0.084C

0.53 ~ 0.56Si

1.97~2.05Mn

0.025 ~0.026P

0.002-0.004S

0.134 ~ 0.136Ti

0.20Mo

0.064 ~0.069Nb

0.001V

0.008 9N)

and the structure of breaking area and base metal is all fenite + minor pearlite with same grain size； the micro crack in breaking area is formed by local plasticity deformation in main crack expanding process ； the formed network proeutectoid ferrite

TiC and TiN are key reason to effect on hot plasticity of casting slab of high Ti microalloying steel. With the measures including in prerequisite of qualified strength of plate to decrease the Ti content in steel from 0. 13% to 0. 11%

secondary water ratio ≤0.9L/kg

temperature of slab at straightening region being more than 950℃ (second brittle zone of the steel- 950 ~ 850 ℃.)

adding holding bell and using slow cooling pit to decrease the cooling rate of slab

the breaking rate of high Ti slab decreases from 10% to 0 to avoid the occurrence of slab breaking.