Continuous Casting
The continuous casting process adopts rectangular billets with a production specification of 350 mm × 470 mm. During production, it is ensured that the tundish preheating time exceeds 2 hours and the tundish temperature is maintained above 1150°C. Proper drying and moisture-proof protection are carried out for mold flux and tundish slag. The tundish is sealed tightly, and argon gas purging is conducted before pouring. The ladle nozzle is also carefully sealed. Tundish slag should be added frequently, and steel liquid surfaces must not be exposed. Submerged pouring is adopted, ensuring an immersion nozzle depth of 120 mm. A reasonable secondary cooling water system is utilized, and the drawing speed is strictly controlled according to the tundish overheating temperature, maintaining a range of 0.46 to 0.50 m/min. The electromagnetic stirring device (M-EMS) for the mold is activated. Depending on the steel overheating temperature and drawing speed, soft reduction is applied appropriately to each strand. Process parameters are carefully configured to ensure high macrostructure quality during continuous casting.
Rolling
The continuously cast billets are delivered hot to the Special Steel 800 Workshop for rolling. They are reheated in a continuous furnace using a mixture of blast furnace gas and coke oven gas as fuel, ensuring effective high-temperature diffusion to promote uniform composition distribution. A two-roll reversible roughing mill (φ800 mm × 1850 mm) is used for rough rolling, followed by a 9000 kN heavy-duty shear. Seventeen no-housing short-stress-line rolling stands are used to produce round bars with diameters ranging from φ90 to 150 mm. Within equipment constraints, the final rolling temperature is controlled to meet grain size requirements of the finished product. The round bars are then straightened using a six-roll bar straightener, and subjected to grinding, inspection, packaging, warehousing, and delivery.
Oxygen Content
Currently, the oxygen content (mass fraction) requirement for this type of steel is controlled below 20×10⁻⁶ domestically and internationally, with advanced levels below 12×10⁻⁶. The oxygen content in the steel is measured following the related standard, with the technical condition requiring no more than 20×10⁻⁶. The oxygen content from two furnace tests showed a maximum of 12×10⁻⁶ and a minimum of 8×10⁻⁶, fully meeting the technical requirements.
Macrostructure
The macrostructure is rated according to relevant standards, and the steel inspection results meet all requirements, as shown in Table 2. No shrinkage cavities, internal cracks, subsurface bubbles, or subsurface inclusions were detected. The degree of macrosegregation and steel density were well-controlled. This demonstrates that measures such as controlling mold and final electromagnetic stirring strength, reducing overheating, and matching the drawing speed have significantly improved the macrostructure quality of the billets.
Post time: Jan-24-2025
