In order to avoid or reduce the surface cracks of 320 mm X 280 mm casting bloom of Nb-Ti microalloying of medium-carbon-boron steel(%/:0.35C

0.04Si

0.87Mn

0.010P

0.007S

0.27Cr

0.031Alt

0.03Nb

0.030Ti

0.0018B

0.0046N)

the high temperature mechanical properties of the bloom are studied

and the microstructure near tensile fracture and impact fracture is observed. The results show that in the range of 600 to 1250℃

the reduction of area of the test steel at 600 °C is 54.4%

and the that at other test temperature points is higher than 60 %. The I brittle zone of the test steel is higher than 1200℃ and HI brittle zone is 750 ~ 850 °C

and at 850 ~ 1200 °C the tested steel has better hot plasticity. The plasticity of tested steel is relatively low at 800 °C

but the tensile fracture is still dominated by dimpled morphology. The surface quality of continuous casting bloom is good in actual continuous casting production with casting speed ≤1.0 m/min and straightening temperature at 950℃