Steel 26CrMoNbTiB is melted by 45 t EAF-LF ( VD) -Φ80 〜180 mm tube billet HCC flow sheet. Test results of cleanliness of the steel at each melting process showed that the oxygen content in steel after LF-VD is (8 ~ 18) x 10
-6
with lowest average inclusion amount i. e. 2. 31 inclusions/mm
2
and that is 3. 66 inclusions/mm
2
in casting billet and the average content of ≥50μm micro inclusions in billet is 4. 08 mg/10 kg. To tighten the sealed shield of long nozzle from ladle to tundish
use monitoring instrument for ladle slagging out
increase tundish capacity and use dam in tundish are the key process measures to further improve cleanliness of billet。