Conversion pig iron: properties, grades and applications

Conversion pig iron is an alloy of iron with carbon (carbon content usually exceeding 2%), intended for further processing into steel or remelting in iron foundries for the production of castings. It is a fundamental intermediate product of the metallurgical process, linking blast furnace production with subsequent steelmaking and foundry units. Unlike foundry pig iron, which is used for the direct production of finished castings, conversion pig iron serves as a feedstock for producing steel and high-quality alloys, and its properties and chemical composition are strictly regulated to ensure the efficiency of further processes.

Chemical Nature and Physicochemical Properties

Conversion pig iron is characterised by a high carbon content (from 3.2% to 5.3% depending on the grade and smelting conditions). Carbon in conversion pig iron is generally in a combined state in the form of cementite (Fe₃C), which gives it a light fracture surface and increased hardness. Such iron is called white iron and is difficult to machine, but it is excellent for remelting into steel, where excess carbon is removed during the oxidative smelting process.

The key impurities determining the quality of conversion pig iron are silicon, manganese, sulfur and phosphorus. Silicon (typically up to 1.5%) affects the steelmaking process, manganese (up to 2%) helps remove sulfur, sulfur (up to 0.07%) is a harmful impurity that reduces the ductility of steel, and phosphorus (up to 2% in phosphoric grades) is also an undesirable element, although in some cases it is used for special purposes. Depending on the application and impurity content, conversion pig iron is divided into grades, which allows metallurgists to select the optimal charge composition for specific technological tasks.

Classification, Grades and Standards

In Russia and CIS countries, requirements for conversion pig iron are established by GOST 805-95 "Conversion pig iron. Specifications", which is harmonised with the international standard ISO 9147-87 in terms of classification by chemical composition. According to the standard, depending on the application and mass fraction of silicon, conversion pig iron is divided into several groups:

• For steelmaking (grades P1, P2). This is the most massive type of conversion pig iron, used for steelmaking in basic oxygen furnaces and electric furnaces. Grade P1 contains silicon in the range of 0.5–0.9%, grade P2 — up to 0.5%. Pig iron of these grades is characterised by low phosphorus (0.1–0.3%) and sulfur (0.01–0.05%) content.

• For foundry production (grades PL1, PL2). This pig iron is used for remelting in iron foundries in the production of castings. It contains more silicon (PL1 — 0.9–1.2%, PL2 — 0.5–0.9%), which facilitates subsequent remelting and the production of high-quality castings. At the consumer's request, the mass fraction of carbon (4.0–4.5%) is standardised for these grades.

• Phosphoric (grades PF1, PF2, PF3). It is distinguished by an increased phosphorus content (up to 2%), which makes it suitable for special applications, for example, for the production of certain types of steel or castings. The silicon content in PF1 is 0.9–1.2%, manganese — up to 2%, sulfur — up to 0.07%.

• High-quality (grades PVK1, PVK2, PVK3). This is pig iron with a particularly low content of harmful impurities (sulfur, phosphorus) and a strictly controlled composition, intended for critical steelmaking and foundry processes.

Conversion pig iron is supplied in the form of pigs (pig iron ingots) weighing up to 18, 30, 45 or 55 kg, which ensures ease of transportation and loading into melting units. The surface of the pigs must be clean, without slag residues.

Production Technology

The main industrial method for producing conversion pig iron is blast furnace smelting. The technological process begins with the preparation of the charge, including iron ore raw materials (sinter, pellets), coke and fluxes (limestone, dolomite). The charge is loaded through the top of the blast furnace, where at high temperatures (up to 2000 °C) iron is reduced from oxides and saturated with carbon.

In the lower part of the furnace (hearth), molten iron accumulates, which is periodically tapped through a taphole. Depending on the smelting parameters (temperature, charge composition, coke consumption), pig iron with different contents of silicon, manganese, sulfur and phosphorus can be produced. Modern blast furnaces are equipped with automatic control and process optimisation systems, which allows high stability of chemical composition and productivity to be achieved.

Considerable attention is paid to reducing the silicon content (to 0.2–0.3%) in conversion pig iron, which facilitates subsequent steelmaking processing and reduces oxygen consumption. To improve the quality of pig iron, desulfurisation and phosphorus removal technologies are used, which is especially important for the production of high-quality grades.

Applications

Steelmaking. This is the absolutely dominant area of conversion pig iron consumption. Pig iron of grades P1 and P2 serves as the main component of the charge for basic oxygen furnaces and electric furnaces, where it is processed into steel by oxidative smelting. The high carbon content provides the necessary reducing conditions and thermal balance of the process, and strict control of impurities allows steel with specified properties to be obtained.

Foundry production. Pig iron of grades PL1 and PL2 is used for remelting in iron foundries. It serves as a raw material for producing grey, high-strength and malleable cast iron, from which housings, beds, machine parts, pipes and other castings are made.

Production of high-quality steels and alloys. High-quality conversion pig iron (PVK) is used for smelting critical steel grades where minimal sulfur and phosphorus content is required. Phosphoric pig iron (PF) finds application in the production of special steels and castings where phosphorus plays a certain technological role.

Other applications. Conversion pig iron is also used for the production of ferroalloys, master alloys and special alloys, as well as a charge component in foundry production to adjust the chemical composition of the melt.

Safety and Storage

Conversion pig iron in massive form (pigs) does not present a chemical hazard. It is non-toxic and non-flammable. The main risks are associated with the heavy weight of the pigs and the need to use lifting equipment during loading and unloading operations, as well as the possibility of injury from falling pigs. When working with pig iron, standard safety measures must be observed: use protective clothing, safety goggles and gloves.

When remelting pig iron in melting units, high-temperature melts and gases are generated, so compliance with safety rules, effective ventilation and the use of personal protective equipment are required. Storage of pigs is carried out on open areas with hard surfacing or in closed warehouses that protect the metal from moisture and contamination. Pigs are stacked in piles while maintaining stability.

Market and Trends

The global conversion pig iron market is an important segment of the metallurgical raw materials market. The largest exporters of merchant pig iron are Brazil, India, Russia and CIS countries. According to industry estimates, Brazilian conversion pig iron is exported at prices in the range of USD 480–490 per tonne FOB, while Russian and CIS pig iron is offered to Turkey at prices above USD 400 per tonne CFR. Indian pig iron acts as the main price competitor, and the Turkish market remains the most active demand centre.

Key industry trends are the tightening of environmental requirements and the reduction of harmful impurities (sulfur, phosphorus), which stimulates the introduction of desulfurisation and purification technologies, as well as the reorientation of logistics flows to domestic markets and new sales channels. Under sanctions restrictions and rising freight costs, Russian producers face logistical challenges but remain competitive due to product quality and flexible pricing policies. Producers with a full metallurgical cycle and access to modern technologies occupy stable positions.

Conclusion

Conversion pig iron remains a fundamental raw material of global metallurgy, ensuring the production of steel and high-quality castings. Understanding the grade composition according to GOST 805-95, blast furnace smelting technologies and quality requirements is the basis for competent material selection and the organisation of efficient supplies. Selecting the pig iron grade for specific technological tasks and organising logistics requires an individual approach taking into account impurity content and further processing conditions.