A Brief Discussion on the 6 Steps of Converter Steelmaking

Converter steelmaking uses molten iron, scrap steel, and ferroalloys as the main raw materials, relying on the physical heat of the molten iron itself and the heat generated by chemical reactions between molten iron components, without external energy, to complete the steelmaking process in the converter. Converter refractory materials are divided into acidic and basic types. According to the position where gas is blown into the furnace, there are top-blown, bottom-blown, and side-blown converters. According to the type of air, there are air converters and oxygen converters, basic oxygen top-blown and top-bottom combined blown converters. Due to their fast production speed, large output, high single furnace capacity, low cost, and low investment, they are the most commonly used steelmaking equipment. Converters are mainly used for producing carbon steel, alloy steel, as well as copper and nickel smelting.

Converter steelmaking is a crucial and technically complex production process involving multiple stages such as raw material selection, pretreatment, and alloy smelting, each step affecting the final quality and performance of the steel.

This article will provide a detailed introduction to the full-process converter steelmaking production flow, taking you on a wonderful journey from raw materials to finished products.

1. Pretreatment Stage: Raw Material Selection and Sampling,

The full-process steel plant's converter production begins with raw material selection. Workers select suitable raw materials from the pig iron pile, ensuring their chemical composition and physical properties meet smelting requirements. Then, technicians sample and analyze the raw materials. Through precise chemical testing, key indicators such as carbon content, silicon content, and manganese content are determined to provide data support for the subsequent smelting process. Raw material pretreatment is necessary before feeding into the converter. Pretreatment mainly includes impurity removal, crushing, drying, etc., aiming to remove impurities from the raw materials, improve uniformity and smeltability, and reduce moisture content to lower energy consumption and waste emissions during smelting.

2. Furnace Area Processing Stage: Charging and Feeding,

Inspect the furnace lining and light-moving equipment and carry out necessary repairs. The pretreated raw materials are fed into the converter. The converter lining is made of refractory materials that can withstand high temperatures and chemical erosion. During charging, workers use special charging equipment to evenly distribute the raw materials inside the converter. During smelting, appropriate amounts of scrap steel, ferroalloys, and other auxiliaries are added as needed to adjust the composition and properties of the molten steel. Heating is usually provided by oxygen combustion. As the temperature rises, the raw materials begin to melt and undergo chemical reactions. At this time, workers blow oxygen into the converter to create a strong oxidizing atmosphere, promoting the oxidation and removal of impurity elements. Oxygen blowing is one of the key steps in converter steelmaking, directly affecting the purity and quality of the molten steel.

3. Control of Acidity and Alkalinity.  

During smelting, to maintain a stable furnace environment and improve molten steel quality, the acidity and alkalinity of the slag need to be controlled. Workers add appropriate amounts of basic minerals such as limestone and dolomite or acidic substances such as silica and bauxite to adjust the slag's acidity and alkalinity. Controlling acidity and alkalinity is important for preventing furnace lining erosion, reducing impurity content, and improving molten steel purity.

4. Smelting Operation Stage: Lowering the Lance and Starting Blowing,

When the raw materials inside the converter have melted and reached a certain temperature, workers start the oxygen lance to perform the lowering and blowing operation. The oxygen lance is one of the core devices in converter steelmaking, driving the stirring and mixing of furnace materials by injecting a high-speed oxygen stream. Lowering the lance and starting blowing marks the beginning of the smelting process and is a key step in controlling the smelting rhythm and molten steel quality. During blowing, intense chemical reactions occur inside the furnace; impurities such as carbon, silicon, and manganese are oxidized and removed by oxygen, while harmful elements like sulfur and phosphorus in the molten steel are also eliminated. During blowing, workers adjust the oxygen lance's blowing intensity and duration as needed to ensure the molten steel's composition and properties meet requirements. The first batch of slag is added simultaneously. Initially, the furnace noise is loud, red smoke emerges from the furnace mouth, followed by dark red flames. The sun reaction intensifies, the furnace mouth flames grow larger and higher, while slag melting reduces noise. After 3-5 minutes, the second batch of slag is added to continue refining.

5. Tapping and Sampling

When blowing reaches a certain stage, workers stop the oxygen lance and perform tapping and sampling. Tapping and sampling is an important step in molten steel smelting. It is used to test the temperature and chemical composition of the molten steel. Workers use special samplers to take a certain amount of molten steel from the converter and send it to the laboratory for analysis. Based on the test results, workers can judge whether the molten steel quality meets requirements and adjust subsequent smelting operations accordingly.

6. Steel Tapping and Alloying

When the molten steel's temperature and composition reach the predetermined requirements, steel tapping can begin. During tapping, workers operate the ladle car to pour the molten steel from the converter into the ladle. To improve steel performance and meet user needs, appropriate alloying elements are added to the molten steel during tapping. The types and amounts of alloying elements depend on the steel grade and application. Alloying elements calculated are added to the ladle for deoxidation and alloying. After finishing tapping into the ladle, the furnace slag is poured in to block the ladle mouth. Molten iron and scrap steel are added, oxygen is supplied to the lance to start blowing. After 3-5 minutes of blowing, the first batch of slag melts, then the second batch is added. If slag melting is poor inside the furnace, a third batch of fluorite slag is added.