What Is The Process of Ladle Refining?

The process of ladle refining is a type of steelmaking process - refining outside the furnace.

Refining outside the furnace divides traditional steelmaking into two steps. The first step is called primary refining, which is to melt, dephosphorize, decarburize and alloy the charge in an oxidizing atmosphere;

The second step is called refining, in which the refining furnaces deoxidizes, desulfurizes, removes inclusions, denatures inclusions, fine-tunes the composition, and controls the temperature of the molten steel in a vacuum, inert atmosphere or controlled atmosphere. Today we will learn about its refining process together.

The Process of Ladle Refining

(Take the ladle refining process of a certain automobile steel production line as an example)

1. Ladle preparation & primary refining molten steel lifting

• Ladles pretreatment: After checking the ladles condition, use magnesium refractory material lining, pre-install lime aluminum slag modifier (CaO:Al₂O₃=6:4), and blow argon gas at the bottom to check the permeability.

• Molten steel hoisting: steel is tapped from the converter to the ladle (including fine-tuning of alloys after the furnace), with argon sealing protection throughout the process to prevent secondary oxidation.

2. Conventional refining stage

• Ladles slag modification: lime (CaO ≥ 90%) and fluorite (CaF₂) are added to adjust the slag basicity to 4 - 6. After the white slag is formed, calcium silicon wire (Si:Ca=3:1) is fed for deep deoxidation.

• Bottom argon stirring: argon gas (flow rate 20 - 50L/min) is blown through porous bricks to even out the composition of molten steel and promote the floating of inclusions.

• Alloying: the amount of FeMn, FeCr and other alloys added is calculated according to the target composition, and the wire feeder is used for precise addition (error ±0.01%).

3. Vacuum refining (taking RH method as an example)

(Note: RH method focuses on ultra-low carbon steel production)

• Vacuum degassing: insert RH immersion tube, control vacuum degree at 1 - 10kPa, circulation flow ≥300t/h, dehydrogenation rate reaches more than 60%.

• Carbon deoxidation: reduce oxygen in steel to below 15ppm by carbon-oxygen reaction (C+O→CO↑) under vacuum in refining furnaces, and adjust [C] to target value simultaneously.

• Temperature compensation: use electrode heating (power 5 - 8MW) or aluminum shot heating to control molten steel superheat ≤30℃.

4. Deep treatment & soft blowing

• Calcium treatment: feed silicon calcium barium wire (Ca:Si:Ba=35:30:5) to change the alumina inclusion morphology to spherical (CaOAl₂O₃SiO₂ system).

• Soft argon blowing seal: let it stand for 5 minutes before the end of refining, and blow argon at a low flow rate (5-10L/min) to suppress vortex and reduce the risk of slag rolling.

5. Quality inspection & steel tapping

• Rapid analysis: spectrometer detects elements such as [C], [S], [O], and X-ray fluorescence analyzes the modification effect of inclusions.

• Temperature confirmation: infrared thermometer multi-point measurement to ensure the continuous casting start temperature deviation of ±5℃.

• Steel tapping connection: the ladle car is transferred to the continuous casting table and covered with carbonized rice husk for insulation.

From the above, it can be seen that the process of ladle refining is: the primary steel from the converter is transported to the refining furnace, and the ladle slag is modified and white slag is refined. The quality of the steel is optimized by controlling the atmosphere in the furnace, proper stirring, alloy fine-tuning and narrow composition control. 

The purpose of refining is to degas, deoxidize, desulfurize, remove inclusions, and accurately control the temperature and alloy composition. Common refining process technologies include ladle argon blowing, CAS method and RH method.