Abstract: 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.

摘要： 700 MPa Ti微合金化低碳钢230 mm连铸板坯的冶金流程为KR铁水预脱硫-210 t BOF-LF-RH-CC工艺。发现放置的板坯横向中间部位断裂。铸坯成分、组织、气体、夹杂和热塑性分析结果表明,中心与其他部位成分一致（/%: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）,断裂与基体组织均为铁素体+少量珠光体,晶粒尺寸相同;断裂处的微裂纹为主裂纹扩展过程产生局部塑性变形形成的;钢中网状先共析铁素体和TiC,TiN是影响高Ti微合金钢连铸坯热塑性的重要原因。在保证成品钢板强度的前提下将钢Ti含量由0.13%降至0.11%,二冷比水量≤0.9 L/kg,板坯矫直段温度高于950℃（该钢第2脆性区为950~850℃）,加保温罩和使用缓冷坑降低板坯冷却速度,使高Ti钢板坯断坯率从10%降至0,避免发生断裂现象。

关键词: Ti微合金化, 连铸板坯, 断裂, 热塑性, 网状先共析铁素体, TiN, TiC, 工艺改善