Process Practice of Long Nozzle Shielding Pouring for Φ210 ~ 310 mm Tube Bloom Casting

The production process flowsheet of tube bloom for 12Mn4V, 37Mn, 26CrMo48V etc steels is 150 t EAF- LF-VD-Φ210 -310 mm round bloom casting. Due to the factors including argon shielding no-close etc, during 150 t ladle to 26 t tundish process the increment value of nitrogen content in liquid AN fluctuates largely, the largest AN is up to 65 ×10^-6. With using the measures including improving shroud cleaning implement, increasing mechanical arm counterbal- ance, improving tight tough touch of ladle flow mouth and shroud, and maintaining argon flow rate 120 L/min and pressure 0. 05 MPa, the increment value of nitrogen content in liquid from ladle to tundish is stably less than 5 ×10^-6, and the ni- trogen content in casting tube bloom is 30 ×10^-6 – 60×10^-6.