Ladle Metallurgy and Hot Metal Pretreatment Technologies

Ladle Metallurgy and Hot Metal Pretreatment Technologies

Ladle metallurgy and hot metal pretreatment are two major process technologies that have developed rapidly in the steel industry since the mid-20th century. In the early 1990s, we collectively referred to both technologies as “secondary metallurgy.” Over more than a decade of domestic and international exchanges, this terminology has gradually gained wide recognition within the steelmaking community.

Secondary metallurgy refers to a series of metallurgical techniques used to improve the physical and chemical properties of hot metal and molten steel by more economical and effective means after they are produced in primary furnaces such as blast furnaces, basic oxygen furnaces, or electric arc furnaces. Its scope includes:

• Hot metal pretreatment: Removing silicon, phosphorus, and sulfur, or enriching elements such as vanadium, titanium, or phosphorus in high-P hot metal within the iron runner, hot-metal transport ladles, torpedo cars, hot-metal ladles, or specialized pretreatment converters. This step also removes slag enriched with these elements.

• Steel refining: Adjusting steel temperature and composition in the ladle (or refining ladle), removing gases, harmful elements, and inclusions to achieve clean, uniform, and stable molten steel.

• Tundish metallurgy: Promoting inclusions and gases to float out and stabilizing the molten steel temperature during continuous casting.

• Mold metallurgy: Further removing inclusions during solidification, promoting nucleation, and ensuring uniform 3. crystallization.

Therefore, efficient secondary metallurgy is not only fundamental to guaranteeing final product quality but also shortens and streamlines the steelmaking process, allowing tighter scheduling and higher efficiency. Together with the basic oxygen furnace, ultra-high-power electric arc furnace, and continuous casting, secondary metallurgy is recognized as one of the four process technologies that revolutionized modern steel production. These technologies are interdependent and mutually reinforcing, forming the solid technological foundation of today's steelmaking industry.

Development History of Ladle Metallurgy and Hot Metal Pretreatment

Early Development (1930s–1950s)

The concept of refining molten steel outside the primary furnace emerged as early as the 1930s–40s.

Representative developments include:

• Synthetic slag refining, first applied in the 1930s and still widely used today.

• Vacuum ingot casting, reported in the early 1940s.

• In the late 1950s, breakthroughs in high-capacity steam ejector pumps enabled the development of DH (degassing in the ladle by lift) and RH (circulating vacuum degassing) processes.

Rapid Growth (1960s–1970s)

The 1960s and 70s witnessed a major expansion of ladle-refining techniques. The driving factors included:

• The introduction of the “clean steel” concept,

• Increasing quality and performance demands from industrial, construction, military, and transportation sectors,

• And the rapid adoption of continuous casting, which required higher-quality molten steel.

During this era, secondary metallurgy underwent three fundamental changes:

1. From supplementary to essential technology

Initially aimed at producing special steel grades that primary furnaces struggled to achieve, ladle refining gradually became indispensable for producing a wide range of steel grades and for overall quality improvement.

2. Critical for stabilizing continuous casting

Secondary metallurgy greatly reduced phosphorus, sulfur, and harmful gases and inclusions, stabilizing continuous casting and reducing process defects.
For example, at Nippon Steel’s Oita Works, all molten steel was treated with RH during the early stage of its full continuous-casting transition, ensuring stable quality and operation.

3. Formation of vacuum and non-vacuum process families

Key processes developed during this period include:

• Vacuum processes: VOD, VAD, ASEA-SKF, RH-OB, etc.

• Non-vacuum processes: AOD, LF furnaces coupled with UHP EAFs, VD processes, injection metallurgy (SL, TN, KTS, KIP), cored-wire addition, and blowing-argon methods such as SAB, CABT, CAS.

• Hot metal pretreatment technologies also progressed rapidly, forming an integrated system with steel refining to reorganize and optimize the entire steelmaking process.

Modern Advancement (1980s–Present)

Since the 1980s, ladle metallurgy and hot metal pretreatment have become essential indicators of a steel plant’s technological level. Their development has focused on broader functionality, higher efficiency, and improved metallurgical performance. Key technologies include:

• RH-KTB, RH-MFP, RH-O, RH-PB, and WPB deep-desulfurization and deep-dephosphorization processes;

• V-KIP and advanced AOD processes;

• Hot metal dephosphorization, desulfurization, and vanadium extraction in specialized converters, such as:

               Sumitomo’s SRP process,

               Kobe Steel’s H-converter,

               Panzhihua Iron & Steel’s vanadium-extraction converter in China.

Main Drivers of Secondary Metallurgy Development

1. The rapid rise of continuous casting

Secondary metallurgy is essential for providing clean, stable molten steel with controlled temperature and composition, thereby ensuring consistent continuous-casting operations.

Japan’s data illustrates this trend:

The simultaneous rise of both ratios clearly demonstrates their close correlation.

2. Demand for advanced steel grades and specialized production

The production of ultra-low-carbon, deep-drawing, ultra-low-phosphorus, and ultra-low-sulfur steels requires optimized process routes that include secondary metallurgy, making it a key driver of rapid technological advancement.