To counter the situation of longitudinal crack defect usually occurred on bloom (wide side 550 mm

narrow side 440 mm

waist 90 mm) in H-shape steel Q235B (0. 14% ~0. 18%C) casting at Jinxi Iron and Steel works

based on original mold powder (% : 29~30Si02

25 ~26CaO

10 ~ 11A12O3

3. 0 ~ 3.5Fe

2

O

3

15 ~ 17C

≤0.5H

2

O)

a high performance mold powder (% : 37. 50Si0

2

37. 50CaO

6A1

2

O

3

7CaF

2

12Na

2

O

7 graphite

1. 5 carbon black) is developed by orthogonal experimental and optimum design. As compared with original mold powder

the semi-sphere point temperature

viscosity and melting time of improved mold powder decrease respectively to 1 092 ℃

0. 27 Pa • s and 32. 5 s from original 1 167℃

0. 77 Pa • s and 57

s. Application shows that as casting speed increase from 0. 98 m/min to 1. 2 m/min

the bloom has high quality by using the improved mold powder.