In order to reduce the defect such as comer crack of rectangular bloom and breakout to increase the quality of bloom

the study of optimization of mould flow field by changing nozzle angle of submerged nozzle has been carried out. The numerical simulation of liquid flow and solidification coupling process in mould for 150 mm x 380 mm rectangular bloom has been performed by using Fluent software to get the effect of nozzle angel (15°-30°) on surface flow rate

surface turbulent kinetic energy and impact depth. Results show that with increasing nozzle angle the average surface flow rate decreases

the impact depth increases being favourable to stabilize the liquid surface ； but with increasing nozzle angle

the liquid surface fluctuation is small

it is unfavourable to stirring liquid and removing inclusions in steel

and in this case the circle round region in lower part of mould is too low and the bloom shell is thinning easily forming breakout ； to sum up it is obtained that the suitable nozzle angle for 150 mm X 380 mm bloom casting is 25°. Application results obtain that the total inclusion numbers with using optimized nozzle decrease by 36%.