Abstract: The defects caused by high hydrogen content were obtained in the flaw detection of ultra large scale continuous casting round billets for wind power tower with a diameter not less than 800 mm. The variation law of hydrogen content in steel throughout the entire process was studied by detecting the moisture content of raw and auxiliary materials and using the Hydris hydrogen analyzer. The results showed that moisture in raw and auxiliary materials, a damp furnace gas atmosphere, and incomplete decomposition of refractory materials are the main sources of hydrogen content in castings. To reduce the hydrogen content of the casting billet, the following process improvement measures were proposed. After 8 minutes of blowing in the converter, raw materials should not be added or added baked one. In the LF refining process, less raw and auxiliary materials are input. Before entering the VD process, a small amount of slag should be controlled. After breaking the vacuum, low-speed wire feeding should be carried out to control the number and type of wire feeding within a small range. Bake the continuous casting tundish at low heat for 60 minutes and clean the air holes in the tundish regularly. After process optimization, the hydrogen mass fraction of molten steel was not exceed 3.6×10^-6 when arriving at the VD station, and not exceed 0.77×10^-6 when leaving the VD station. In the molten steel of the continuous casting tundish, the hydrogen mass fraction of the first furnace was not exceed 2.0×10^-6, and not exceed 1.6×10-⁶ in the second furnace, and not exceed 1.1×10^-6 in the continuous casting furnace. Therefore, the hydrogen content of the continuous casting round billets for ultra large scale wind power tower was reduced successfully, ensuring the quality of the finished forgings. 

Key words: hydrogen content, flaw detection, continuous casting round billets, raw and auxiliary materials