Steel ingots are known as semi-finished products in the steel industry, playing a fundamental role in the production of a wide range of final steel products. These steel pieces are produced in specific geometric shapes with various dimensions and weights and are used as raw materials for manufacturing products such as rebar, I-beams, sheets, etc. Steel ingots are essentially the first solid and transportable form of steel after the steelmaking processes, and for this reason, they hold a special place in the steel industry's supply chain. The appearance of ingots is often rectangular or trapezoidal, a design intended to facilitate transportation and separation from casting molds. The quality and characteristics of steel ingots directly affect the properties and quality of the final steel products.
The consistent emphasis in various sources on the "semi-finished" nature of steel ingots indicates their intermediary role and their dependence on subsequent processing stages to become usable final products. The production chain is as follows: raw materials are converted into steel and then cast into ingots. These ingots are not the final product and undergo shaping processes to produce various forms such as sheets, rebars, and profiles. This sequential nature means that any disruption in the ingot production stage can have a ripple effect on the availability and cost of final steel products. Furthermore, the mention of different ingot shapes (rectangular, trapezoidal, and implicitly other shapes like square and round in later sections) at the beginning of the definition shows that the appearance is not random but likely optimized for specific transportation, casting, or downstream processing needs. The trapezoidal shape, mentioned for ease of demolding and transportation, highlights practical considerations in ingot design. Other shapes, which will be discussed later in the context of billets, blooms, and slabs, likely cater to the specific requirements of the rolling or forging processes they will undergo.
The production of steel ingots is a complex, multi-stage process involving melting, refining, casting, and solidification.
Melting: In this stage, raw materials such as iron ore, scrap iron, and sponge iron are melted in various furnaces, including blast furnaces, electric arc furnaces (EAF), or induction furnaces. In a blast furnace, iron ore, coke, and limestone are typically used to produce molten iron, which is then converted into steel. The molten iron from a blast furnace has a high percentage of carbon and other impurities. In contrast, electric arc furnaces use scrap iron and sponge iron as raw materials and often allow for the addition of various alloys. Induction furnaces also melt scrap iron by creating a magnetic field. The choice of furnace depends on factors such as cost, desired metal quality, production needs, and the type of alloy to be produced. Over 90 percent of the world's extracted iron ore is used in blast furnaces.
Refining: After melting, the molten steel is refined to remove impurities. These impurities include elements such as carbon, sulfur, and phosphorus. In blast furnaces, the refining process involves blowing pure oxygen at high speed into the molten iron, a process known as basic oxygen steelmaking. This oxidizes excess carbon and other impurities. Limestone is also added to the melt to absorb more impurities, which combine with it to form slag. In electric arc furnaces, oxygen blowing is also used to remove carbon. In these furnaces, sampling, oxygen blowing, homogenization, and analysis of the molten material are performed to convert the contents of the furnace into molten steel. The refining stage ensures that the steel produced has the required chemical composition for its intended application.
Casting: In this stage, the refined molten steel is poured into molds to solidify into steel ingots. There are two main methods for casting steel ingots: ingot casting in individual molds and continuous casting. In ingot casting, molten steel is poured separately into molds, which are usually tapered to facilitate the removal of the ingot. This method is often used for low-volume production or special steels. In contrast, continuous casting is a more efficient process for high-volume production. In this method, molten steel is continuously poured into a water-cooled mold, producing a continuous strand of semi-finished steel (billet, bloom, or slab) that is then cut to the desired lengths. The shape and size of the mold at this stage are crucial for subsequent shaping processes. The method of casting and solidification of the molten material also affects the mechanical and physical properties of the final product.
Solidification and Cooling: After casting, the steel ingots are left to solidify and cool. The cooling rate can affect the microstructure and properties of the steel. In the continuous casting method, the solidified pieces are continuously withdrawn from the end of the mold at the same rate as the pouring. Water spraying is used to accelerate the cooling process in continuous casting. Finally, the solidified ingots are cut to the desired lengths.
The prevalence of continuous casting, as mentioned in multiple sources, indicates a modern trend towards increased efficiency and higher production rates in steel ingot manufacturing compared to the traditional ingot casting method, also referred to as "manual casting." Continuous casting allows for a smoother process where molten steel is continuously transformed into semi-finished products, reducing the need for handling individual molds and potentially improving material yield. The mention of manual casting being suitable for small workshops reinforces the idea that continuous casting is the dominant method for large-scale production. Additionally, the reference to different furnaces (blast furnace, electric arc furnace, induction furnace) shows that the production process can be tailored based on the available raw materials and the desired quality and type of steel. This demonstrates the flexibility and adaptability of the steelmaking industry. Blast furnaces typically rely on iron ore, while electric arc furnaces use scrap. This difference suggests that regions with abundant iron ore resources might favor blast furnaces, while those with well-developed scrap recycling infrastructure might prefer electric arc furnaces. Furthermore, the ability of electric arc furnaces to produce alloy steels indicates their importance in specialized applications requiring specific material properties.
Steel ingots are divided into different categories based on their shape and intended application. The three main types of ingots that are most commonly used are billets, blooms, and slabs.
Billet: A billet, also known as a bloomlet, is a type of steel ingot that typically has a square or circular cross-section with a width or diameter of less than 150 millimeters (some sources mention less than 15 centimeters or an area of less than 230 square centimeters). Billets are longer in length compared to traditional ingots. The main application of billets is in the production of long products such as rebar (reinforcing bar), wire rod, strip, and small sections. Billets are produced in various grades such as SP3 and SP5, where grade SP3 has higher flexibility and grade SP5 has higher strength. Common billet sizes include 100x100 mm, 125x125 mm, and 150x150 mm.
Bloom: A bloom, sometimes also called a billet or a blank, is similar to a billet but has a larger square or rectangular cross-section (width or diameter greater than 150 millimeters or an area greater than 230 square centimeters). Blooms are used for producing structural sections such as I-beams, channels, angles, rails, and other profiles. Sometimes blooms are also produced by cutting the edges of slabs. Common bloom sizes include 180x180 mm, 200x200 mm, and 250x250 mm.
Slab: A slab is another type of steel ingot that has a rectangular cross-section with a width much greater than its thickness (e.g., length 4 to 12 meters, width around 1.25 meters, and thickness around 230 millimeters). The main application of slabs is in the production of flat products such as steel sheets, plates, strips, and coils. Different grades of steel sheets are produced based on the carbon content in the slabs. Slab is considered one of the most important raw steel products.
Other Types: In addition to the three main types, there are other types of steel ingots that are categorized based on their production method, chemical composition, or application:
Manual Ingot: These ingots are cast manually and usually have a trapezoidal cross-section and a shorter length (up to 2 meters), suitable for small workshops.
Carbon Steel Ingot: This type of ingot contains 0.2% to 2.1% carbon and is used in construction, industrial machinery, and automotive industries due to its strength and reasonable price.
Alloy Steel Ingot: In the production of these ingots, elements such as chromium, nickel, molybdenum, and vanadium are used to improve properties like strength, hardness, and resistance to corrosion and heat, and they are used in aerospace, automotive, and specialized machinery manufacturing industries.
Tool Steel Ingot: This type of ingot is specifically designed for the production of tools, molds, and cutting equipment and has high strength, hardness, and wear resistance, containing elements such as tungsten, molybdenum, vanadium, and cobalt.
Electrical Steel Ingot: These ingots are used for the production of electrical products such as transformers, generators, and motors and have unique magnetic properties and high electrical energy distribution speed.
5SP Ingot: This specific grade of steel ingot is used in various industries and originates from the Russian standard (GOST), having specific mechanical and chemical properties that can vary depending on the region. It is generally used for the production of rebars up to size 25.
3SP Ingot: This other grade is known for its higher flexibility compared to other grades and is often used for the production of angles, channels, and smaller size rebars (such as 8 and 10).
The distinction between billets, blooms, and slabs based on cross-sectional dimensions and intended downstream products indicates the existence of a standard in the steel industry that allows for efficient allocation of semi-finished materials to specific production processes. Knowing the type of raw material (billet, bloom, or slab) immediately specifies the kind of final products that can be efficiently produced from it, optimizing the production flow. Also, the existence of different steel grades within the ingot category (like 3SP, 5SP, carbon steel, alloy steel, tool steel, electrical steel) shows that steel ingots are not a monolithic product but are chemically tailored to meet the specific performance requirements of diverse applications. The varying alloying elements and carbon percentages in each grade result in distinct mechanical, chemical, and magnetic properties. For example, the higher carbon content in carbon steel ingots makes them suitable for structural applications, while the addition of chromium in alloy steel ingots provides corrosion resistance for harsher environments.
Table 1: Key Differences Between Billet, Bloom, and Slab
Ingot Type | Typical Cross-Section | Typical Max Width/Diameter | Main Applications |
| Billet | Square or Circular | < 150 mm | Rebar, Wire Rod, Small Sections |
| Bloom | Square or Rectangular | > 150 mm | Structural Sections (I-beams, Channels, Angles, Rails) |
| Slab | Rectangular (Width >> Thickness) | Width typically around 1.25 meters | Flat Products (Sheets, Plates, Strips, Coils) |
Steel ingots are used as a fundamental raw material in various industries.
Construction: In the construction industry, steel ingots play a vital role. They are used to produce reinforcing steel bars (rebars) that provide the necessary tensile strength for concrete structures. Also, structural steel sections such as I-beams, channels, and angles, which are essential for constructing the steel frames of buildings and other structures, are produced from steel ingots. Steel pipes used for water and gas transmission in buildings can also be produced from steel ingots. Steel sheets, obtained from slabs, are used in various construction applications, including roofing and wall cladding. Furthermore, steel derived from ingots is also used to manufacture railway tracks. The carbon content in the steel ingot is an important factor in determining the properties of the rebar produced for the construction industry.
Automotive: The automotive industry is one of the largest consumers of steel, and steel ingots are used as raw materials for producing various car parts, including chassis, body, wheels, brakes, exhaust systems, and engine components. Different types of steel derived from ingots are selected based on the required strength, weight, and formability for each specific part. For example, high-strength low-alloy steel is used for car bodies and frames, and carbon steel is used for gears. Also, galvanized steel is used for car body and roof construction due to its corrosion resistance, and stainless steel is used in parts like exhaust systems.
Manufacturing: Steel ingots also have extensive applications in the manufacturing sector. They are used to produce industrial machinery parts, tools, and various equipment. Steel pipes and tubes used for various industrial applications, including in the oil and gas industries, are also produced from steel ingots. Additionally, wire rods, fasteners, and other metal parts are made from this raw material. Forging and extrusion processes also use steel ingots to create different shapes and components. In the shipbuilding industry, steel produced from ingots is used to construct the hulls and structural components of ships. The aerospace industry uses high-strength alloy steels derived from ingots to manufacture critical parts such as shafts, turbines, and engine components.
The widespread use of steel derived from ingots across diverse industries underscores steel's fundamental role as a material due to its versatile properties, which can be tailored through various alloying and processing techniques applied to the initial ingot form. From the basic infrastructure of buildings and transportation to the complex machinery used in manufacturing and the stringent requirements of aerospace, steel's adaptability in terms of strength, durability, and cost-effectiveness makes it an indispensable material. The ingot serves as the starting point for this adaptability. The specific examples of steel types used in the automotive industry (like galvanized steel for the body, stainless steel for the exhaust system, high-strength steel for the frame) illustrate how the initial steel ingot is further processed and potentially alloyed to meet very specific performance criteria for different applications within a single industry. The automotive industry demands a wide range of steel properties, from corrosion resistance to high strength-to-weight ratios. This necessitates the production of various steel types, all originating from steel ingots but undergoing different processing and alloying stages to achieve the desired characteristics for each particular car part.
Steel ingots serve as the primary raw material for the production of almost all final steel products, forming the first solid and transportable shape of steel after the initial steelmaking processes. The quality and chemical composition of the steel ingot directly determine the quality and properties of the final products. Using high-quality ingots leads to the production of superior final steel products. The price of steel ingots significantly affects the cost of all downstream steel products, making it a critical factor in the overall economics of the steel industry. The easy transportability of steel ingots facilitates their use as a raw material for producing various steel sections. Today, steel ingot is considered the most important commodity in the steel production chain.
The repeated statement that steel ingots are the "foundation" or "basis" of other steel products emphasizes their fundamental and essential role in the entire steel value chain. Without high-quality and readily available ingots, the production of a vast array of materials crucial for various industries would be severely disrupted. The analogy to a foundation suggests that the properties and quality of the ingot set the upper limits for the properties and quality of all subsequent products. Any defects or inconsistencies in the ingot are likely to be carried over and potentially amplified in the final steel products. The price sensitivity of final steel products to the price of steel ingots indicates the significant economic leverage that ingot producers hold within the steel industry. Fluctuations in ingot prices can have ripple effects across many sectors, impacting everything from construction costs to the price of automobiles. This price sensitivity stems from the fact that the ingot is the primary raw material for many steel manufacturers. Any increase in the cost of this input inevitably leads to higher production costs for downstream products, which are then passed on to consumers or absorbed by manufacturers, affecting overall market prices.
The production and use of steel ingots are subject to various quality standards and technical specifications. The National Standards Organization of Iran has approved a standard titled "Standard for Continuously Cast Blooms and Billets Used in Structural Steels" with the number 20300. This standard defines different categories, including square blooms, square billets, rectangular blooms, and rectangular billets, based on their dimensions. It also specifies the requirements for chemical composition based on product standards or agreements between the supplier and the buyer. This standard covers dimensional tolerances and permissible surface and internal defects. The standard outlines the information required when ordering (identification, quantity, dimensions, inspection requirements, final application, technical certificate) and the necessary details in the seller's technical certificate (ingot type, production date, melt number, dimensions, quantity, order number, steel grade, chemical composition, test results, production process, certificate of health regarding radioactivity).
In addition to the Iranian national standard, other international standards are used in the steel industry, including DIN (Germany), ASTM (USA), JIS (Japan), BS (UK), GOST (Russia), and AFNOR (France). The technical specifications of steel ingots typically include the steel grade (based on carbon content such as 3SP, 5SP, or specific alloy compositions like CK45, MO40), mechanical properties (tensile strength, yield strength, elongation), and precise dimensions. Chemical analysis of the ingot is very important to determine its suitability for the intended final product. Surface quality standards also dictate that ingots should be free from harmful surface defects such as longitudinal, transverse, and star cracks, as well as internal defects such as gas and shrinkage cavities.
The relatively recent adoption of a national standard for steel billets and blooms in Iran (Standard No. 20300, approved in 1398 after a lengthy development process that began in 1391) indicates a growing emphasis on quality control and standardization in the Iranian steel industry to align with international best practices. The fact that this standard was developed based on local expertise and due to the absence of a direct international equivalent demonstrates a level of self-reliance and adaptation to specific domestic needs. The long development process highlights the complexity and importance of establishing comprehensive standards for such a fundamental raw material. The focus on structural steels produced by continuous casting reflects the prevalence of this production method and the significance of construction applications in the Iranian market. The inclusion of specific requirements for chemical composition, dimensions, and defect limitations aims to ensure uniformity and quality in domestically produced steel ingots. The reference to various international standards (DIN, ASTM, GOST) alongside the Iranian national standard underscores the global nature of the steel industry and the need for interoperability and comparability of steel products across different markets. This suggests that while national standards are important for domestic production, manufacturers must also be aware of and potentially adhere to international standards for export purposes or to meet the specific requirements of international customers. Different countries and regions have developed their own sets of standards based on their specific industrial needs and historical practices. However, the increasing globalization of trade necessitates a degree of harmonization or at least mutual understanding of these different standards to facilitate international commerce in steel products.
Table 2: Overview of Iranian National Standard No. 20300 for Steel Blooms and Billets
Ingot Type | Cross-Section | Size Range (mm) | Steel Grades Covered (e.g., based on Iranian National Standard 1-13280) | Key Requirements (e.g., chemical composition, surface defects) |
| Square Bloom | Square | Sides > 120 | Non-alloy and low-alloy structural steels according to Iranian National Standard 1-13280 | Limits on chemical elements, absence of surface cracks and harmful internal defects |
| Square Billet | Square | Sides ≤ 120 | Non-alloy and low-alloy structural steels according to Iranian National Standard 1-13280 | Limits on chemical elements, absence of surface cracks and harmful internal defects |
| Rectangular Bloom | Rectangular | Area > 14400, width-to-thickness ratio between 1 and 2 | Non-alloy and low-alloy structural steels according to Iranian National Standard 1-13280 | Limits on chemical elements, absence of surface cracks and harmful internal defects |
| Rectangular Billet | Rectangular | Area 2500-14400, width-to-thickness ratio between 1 and 2 | Non-alloy and low-alloy structural steels according to Iranian National Standard 1-13280 | Limits on chemical elements, absence of surface cracks and harmful internal defects |
Using steel ingots as a raw material in the steel industry has both advantages and disadvantages.
Advantages: Steel ingots serve as a versatile and essential raw material for producing a wide range of final steel products in numerous industries. The properties of steel can be controlled and customized by precisely adjusting the chemical composition (such as carbon content, alloying elements) during the ingot production process to meet specific application requirements. Steel offers high strength relative to its weight, making it an efficient and reliable material for various structural applications in construction, automotive, and other sectors. Compared to other metals with similar strength characteristics, steel is generally a cost-effective material, making its use economically feasible in a wide range of applications. Steel is a highly recyclable material, contributing to sustainability and reducing the environmental impact associated with material production. The solid and standardized shape of ingots, compared to molten steel or raw materials, allows for easier handling, storage, and transportation, facilitating efficient logistics in the steel supply chain.
Disadvantages: The presence of impurities or undesirable elements (such as sulfur, phosphorus, copper) in steel ingots can negatively affect the quality and performance of the final products, potentially leading to issues like brittleness, reduced ductility, or decreased resistance to corrosion and fatigue. The production of steel ingots, especially through energy-intensive methods like blast furnaces and electric arc furnaces, can have a significant environmental footprint in terms of energy consumption and greenhouse gas emissions. Steel ingots are semi-finished products and always require further processing (rolling, forging, extrusion) to become usable final products, which adds to the overall production cost and time.
While the sources primarily focus on steel ingots, the mentioned advantages (strength, cost-effectiveness, recyclability) implicitly position steel as a competitive material against alternatives like aluminum, concrete, and composites in various applications. However, the disadvantages (high energy consumption, need for further processing) highlight areas where these alternative materials might offer benefits. For example, while aluminum is lighter than steel, its production is generally more energy-intensive and costly. Concrete, while strong in compression, lacks the tensile strength of steel. Composites can offer tailored properties but may be more expensive and less recyclable than steel. The emphasis on the negative impact of impurities underscores the critical importance of the refining stage in the steelmaking process. Even with steel's inherent advantages, inadequate removal of unwanted elements can significantly reduce its performance and suitability for demanding applications. This highlights the need for stringent quality control measures throughout the production process. The specific examples of sulfur causing brittleness and phosphorus affecting strength and corrosion resistance illustrate how seemingly minor impurities at the ingot stage can have significant consequences for the integrity and longevity of final steel products used in critical infrastructure or machinery.
The price of steel ingots is influenced by several factors in global and domestic markets.
The cost of key raw materials used in ingot production, such as iron ore, iron pellets, concentrate, sponge iron, and scrap iron, significantly affects the final price of ingots. Fluctuations in the prices of these raw materials directly impact production costs and, consequently, the selling price of ingots. Energy costs, including the price of electricity, natural gas, and fuel used in transportation and production processes, play a crucial role in determining the overall cost of steel ingot production and its market price. The balance between supply and demand in domestic and international markets is a fundamental factor in determining the price of steel ingots. Increased demand typically leads to higher prices, while oversupply can result in price decreases. Factors such as economic growth, infrastructure projects, and industrial activities significantly impact demand. Exchange rates, especially the US dollar rate against local currencies, have a significant impact on steel ingot prices, particularly in countries involved in international steel trade. Fluctuations in exchange rates can affect both the cost of imported raw materials and the competitiveness of exported steel products. Global economic conditions and political stability can influence market sentiment and overall demand for steel. Economic downturns may lead to reduced demand and lower prices, while periods of growth can drive prices up. Geopolitical events and trade policies can also create volatility in the steel market. The price trend of final steel products, such as billets and other long products, in the global market can also affect the pricing of steel ingots, as ingots are the primary raw material for these products. Market dynamics and pricing decisions in major steel-producing regions, such as the Commonwealth of Independent States (CIS) countries, can have a significant impact on global steel prices due to their high export volumes. In the Iranian market, the price of steel ingots is also influenced by domestic factors such as the balance of supply and demand within the country, government regulations and policies related to the steel industry, and the performance of key steel-consuming sectors like construction and automotive manufacturing. Steel ingot prices are often announced daily and are based on per kilogram, and they can vary depending on the grade, dimensions, and the producing factory. Market information and price updates are usually available through industry websites and commodity exchanges.
The sheer number of factors influencing steel ingot prices (raw materials, energy, currency, global economy, regional market dynamics) highlights the complex and interconnected nature of the global steel market. Price fluctuations can stem from a wide array of variables, making it challenging to predict future price movements and requiring stakeholders to closely monitor various economic and geopolitical indicators. For example, an increase in global iron ore prices directly impacts the production cost of steel ingots produced in blast furnaces. Similarly, fluctuations in energy prices affect the operating costs of both blast furnaces and electric arc furnaces, influencing ingot prices. Exchange rate volatility can further complicate international trade pricing. The specific mention of the Iranian market and the influence of factors like exchange rates and the performance of domestic industries (construction, automotive) alongside global factors indicates that while global trends have a significant impact, local economic conditions and government policies also play a crucial role in shaping the domestic steel ingot market. For instance, government initiatives to boost the construction sector in Iran could lead to increased demand for steel ingots, potentially driving up prices domestically even if global prices remain stable. Conversely, changes in import tariffs or export regulations could also significantly affect local market dynamics.
Steel ingots, as vital semi-finished products in the steel industry, play a pivotal role in the production of a wide range of final steel products. Their production process involves complex stages of melting, refining, and casting, carried out using various methods and furnaces. The diverse types of steel ingots, including billets, blooms, and slabs, each with their specific characteristics and applications, meet the varied needs of different industries from construction and automotive to manufacturing and aerospace. The quality of the steel ingot directly affects the quality of the final products, and its price plays a significant role in the economics of the steel industry. National and international quality standards have been developed to ensure the production of steel ingots with the required technical specifications. Ultimately, the price of steel ingots is influenced by complex and numerous factors in global and domestic markets, requiring careful monitoring and continuous analysis. As the foundation of steel product manufacturing, steel ingots continue to play a fundamental and undeniable role in the global economy.