The flowsheet for steel SPHC (/% : ≤0.08C

≤0. 05Si

0. 10 ~0. 30Mn

≤0

025P

≤0.025S

0. 020 ~0. 045Al) is hot metal pretreatment- 150 t top and bottom combined blown converter- LF- double strand slab casting process- 1 780 mm hot continuous rolling process. By analysis on nozzle blocking substance it is obtained that the main ingredient of blocking substance is Al

2

O

3

and high melting point (1 750 ℃ ) CaO·2Al

2

O

3

inclusion

the outlet of blocking substance is piled up alumina with loose structure

the middle layer is net type alumina and the inner layer is decarburized zone of nozzle materials. With the process measures including controlling converter end [C

]

> 0. 04%

adjusting feeding calcium wire amount to increase the liquid average c

alcium-aluminium ratio from 0. 03 to 0. 06

increasing soft argon blowing time from 6 ~ 8 min to 8 ~ 10 min and preventing liquid secondary oxidizing in casting process

the results of 48 heats steel SPHC production show that the nozzle blocking accidents are averted.