Carbon steel, due to its outstanding strength, controllable cost, and good adaptability to various processing techniques, is widely used in the industrial field and plays a significant role. This article will systematically elaborate on the main classifications, performance characteristics, and practical application scope of carbon steel to help you have a more comprehensive understanding of it.
What Is Carbon Steel?
Carbon steel is an iron-based alloy mainly composed of iron and carbon, with carbon being the key alloying element. You can think of it as a category of materials that adjust the properties of steel by controlling the carbon content. Generally, the carbon content in carbon steel ranges from 0.05% to 2.1%, and anything beyond this range is classified as cast iron.
Carbon plays a decisive role in it. As the carbon content increases, steel typically becomes harder, less prone to deformation, and has higher wear resistance. Conversely, a higher carbon content reduces ductility, toughness, and weldability. On the contrary, low-carbon steel is softer and easier to shape and weld. The adjustable carbon content of carbon steel allows you to choose the appropriate type of carbon steel based on structural strength, processing methods, and usage environment.
Unlike stainless steel or alloy steel, carbon steel contains almost no alloy elements such as chromium and nickel, only a small amount of silicon, manganese, and other necessary components and trace impurities. This simple composition structure enables carbon steel to have an excellent strength-cost ratio, so it is often used in construction, manufacturing, and industrial fields.
How Is Carbon Steel made?
Step1:Iron smelting in blast furnaces
The production and manufacturing of carbon steel begins with iron smelting. Iron ore, coke, and limestone are layered into the blast furnace. Under high-temperature conditions, the iron ore is reduced to molten iron, coke provides carbon for the molten iron, and limestone is used to remove impurities. At this stage, the product obtained is pig iron, which has a relatively high carbon content and is the basic raw material for manufacturing carbon steel storage tanks, carbon steel welding rods, and other products.
Step2:Primary steelmaking
The pig iron needs further refining. Common methods include the alkaline oxygen converter (BOF) and the electric arc furnace (EAF). To remove excess carbon, the BOF method first adds pure oxygen to the molten iron, reducing the carbon content. After that, harmful impurities such as sulfur and phosphorus can be removed. The EAF method involves using a high-temperature electric arc to melt scrap steel or recycled steel, and its internal composition can be flexibly controlled.
Step3:Carbon content adjustment
During the steel-making process, by controlling the ratio of oxygen to raw materials, the carbon content can be precisely controlled within the range of approximately 0.05% to 2%. Subsequently, carbon steel with different carbon contents can be produced. The carbon content determines the hardness, strength, and ductility of the steel. It has a significant impact on products made from carbon steel, such as the pressure resistance of KDM’s carbon steel storage tanks or the welding effect of carbon steel welding rods.
Step4:Secondary refining treatment
The KDM carbon steel products require high purity, so the molten steel needs to enter the secondary refining stage. To remove harmful gases and residual impurities, in the steel ladle furnace, the temperature and composition need to be adjusted, while stirring, inert gas injection, and degassing treatment are also carried out.
Step5:Deoxidation and casting
Finally, aluminum or silicon is added for deoxidation to prevent gas pores from forming when the steel solidifies. The molten steel is then cast into steel ingots, slabs, or billets, and undergoes natural or controlled cooling.
Step6:Subsequent processing and heat treatment
According to the customer’s requirements, the formed carbon steel can undergo processes such as rolling, forging, annealing, or other treatments. Eventually, these carbon steel materials will be processed into storage tanks, welding rods, and other high-performance industrial products.
Types of Carbon Steel
Low carbon steel (mild steel)
Low-carbon steel, Low carbon steel, also known as mild steel, has a carbon content of approximately 0.05% to 0.25%. It has relatively low hardness but excellent ductility. You can easily perform operations such as stamping, welding, and cutting on it.
Low-carbon steel has a high cost-performance ratio and is widely used in industrial and commercial buildings. In KDM products, low-carbon steel storage tanks and welding rods fully demonstrate their machinability and welding performance.
Heat treatment technology does not apply to low-carbon steel. If hardness needs to be increased, only cold treatment or adding alloy elements (such as copper, nickel, molybdenum, and vanadium) can be used.
Medium carbon steel
The carbon content of medium carbon steel ranges from 0.25% to 0.6%, and the manganese content is from 0.6% to 1.65%. Compared with low-carbon steel, it has higher tensile strength and better wear resistance, and welding requires higher process requirements. Through heat treatment methods such as quenching and tempering, or by adding alloy elements such as chromium, molybdenum, and nickel, hardening treatment can be achieved.
Due to its strong load-bearing capacity, medium carbon steel is always applied to manufacture components that bear large loads, such as mechanical shafts, gears, shaft components, crankshafts, and components related to railway tracks.
High carbon steel
The carbon content of high-carbon steel ranges from approximately 0.6% to 1.25%, and the manganese content is about 0.3% to 0.9%. After heat treatment, high-carbon steel can achieve extremely high hardness. If there is a requirement for welding performance, more specialized processing methods need to be adopted.
High-carbon steel is mainly used in fields that have extremely high requirements for sharpness and wear resistance; cutting tools and industrial knives are always made from it. Furthermore, it is a vital material for manufacturing springs, commonly found in automotive suspensions and other products.
Ultra-high carbon steel
The carbon content in ultra-high carbon steel exceeds 1.25%, and the maximum content can reach 2%. His hardness is very high, but his ductility is very poor. Due to the extremely high processing difficulty, this type of steel is usually only used in specific industrial scenarios and sometimes even as experimental materials.
The Properties of Carbon Steel
Physical Properties
- Density: The density of carbon steelis relatively high, approximately 7.85 grams per cubic centimeter, making it heavy. In structural applications, it has high stability and strong impact resistance. This is particularly important when manufacturing carbon steel tanks and support frames.
- Fusion Point: The fusion point range of carbon steel is between 1425°C and 1540°C. The higher the carbon content, the lower the fusion point, which is suitable for intermittent heat loads or welding processing.
- Thermal and Electrical Conductivity: The thermal conductivity of low-carbon steel is relatively good, while high-carbon steel has a slightly lower thermal conductivity (45–50 watts/meter·kelvin). When considering heat exchange equipment or electrical components, you need to take this factor into account.
Chemical Composition
- Main Elements: Carbon steel is composed of iron and carbon.
- Alloy Elements: A small amount of manganese in carbon steel serves to improve
the strength and toughness of the steel while reducing the adverse effects of sulfur; by adding sulfur, the cutting performance can be improved, but to some extent, it will reduce the ductility. Although phosphorus can also increase the strength, it will increase the brittleness of the carbon steel.
Due to the different chemical compositions of various grades of carbon steel, you can adjust the content of chemical components according to the product. For instance, high manganese medium carbon steel is suitable for manufacturing pressure-resistant storage tanks and high-strength welding rods, while low carbon steel is used for components and pipes that are easy to shape.
Strength and Performance Characteristics
- Hardness and strength grade: Low carbon steel has moderate strength but excellent ductility; medium carbon steel has both strength and certain ductility; high carbon steel has extremely high hardness but poor ductility; ultra-high carbon steel has the highest hardness but is very brittle.
- Plasticity: The elongation of low-carbon steel is greater than 25%, while the elongation of high-carbon steel after hardening is less than 10%.
Heat treatment effects
- Annealing: The purpose of annealing is to make carbon steel softer. First, heat the steel to the specified temperature, keep it for a certain period of time, and then let it cool naturally. This not only enhances the plasticity of the steel but also facilitates processes such as cutting, shaping, and welding. To achieve the appropriate grain structure, high-carbon steel is typically heated to approximately 738°C, while low-carbon steel is heated to approximately 840°C.
- Hardening: Rapidly cooling the steel to form a hard martensite structure, which improves the hardness of the steel.
- Tempering: Reduces the brittleness of carbon steel. The heating degree can be determined by color, and then it is quickly cooled with cold water.
Corrosion resistance and recyclability
- Carbon steel has average corrosion resistance in neutral environments, but it may rust in acidic or alkaline conditions. Therefore, protective measures such as galvanization, painting, or powder coating need to be taken.
- Carbon steel can be recycled and reused. Used steel is collected and melted, and then undergoes secondary processing. Its performance is generally not affected. At the same time, recycling carbon steel can save iron ore and energy, and lower harmful gas emissions in steel production.
Strengths and Weaknesses of Carbon Steel
Strengths of Carbon Steel
High strength and durability
The mechanical strength and wear resistance of carbon steel are very strong. It possesses strong mechanical strength and outstanding wear resistance. Therefore, it is often used to manufacture storage tanks, welding rods, mechanical parts, and structural beams. Compared with other materials, carbon steel products rarely experience cracking or damage.
Affordable
The raw material cost of carbon steel is much lower than that of stainless steel or special alloys. For large-scale production projects, such as pipelines and storage tanks, carbon steel has an advantage in terms of cost.
Multifunctionality and Machinability
During the processing, carbon steel exhibits flexibility. Through processes such as cutting, shaping, welding, and heat treatment, it can be used to manufacture high-precision components. Low-carbon steel is easy to weld into shape; medium-carbon steel and high-carbon steel, after undergoing heat treatment, have higher hardness and toughness, and are suitable for tools and wear-resistant components.
Sufficient Supply and Rich Variety
Carbon steel raw materials are abundant, and the supply chain is mature, so you can obtain it at any time. Carbon steel comes in various specifications and grades. In KDM, you can customize products according to the requirements of various characteristics of carbon steel.
Heat Resistance and Thermal Performance
The hardness of high-carbon steel does not change with the increase in temperature. The thermal and electrical conductivity of carbon steel can also meet the requirements of some industrial applications, and it is more operable in manufacturing and equipment operation.
Weaknesses of Carbon Steel
Limited Corrosion Resistance
Carbon steel without coating or galvanization is prone to rusting. When used in humid, marine environments, additional protection is required; otherwise, the lifespan will be shortened.
Brittleness of High-Carbon Steel
An increase in carbon content will enhance hardness and tensile strength but reduce ductility. High-carbon steel may develop cracks when subjected to impact or bending stress, and flexible components are not made of high-carbon steel.
Welding and Forming Challenges
Low carbon steel has excellent welding performance, but high carbon steel, because of its high hardness, is prone to cracking during welding and requires preheating, post-weld heat treatment, or special welding materials. High-carbon steel has poor forming ability and is more difficult to process.
Heavier in weight
The density of carbon steel is approximately 7.85 grams per cubic centimeter, which is heavier than that of aluminum or many alloys. It might require some effort in transportation and handling.
High Surface Treatment Needs
Untreated carbon steel surfaces oxidize and rust easily. To make the surface smoother, additional processing steps such as painting, galvanizing, or powder coating are usually required.
The Applications of Carbon Steel
Architecture and Infrastructure
Low-carbon steel is a staple in construction, ideal for components like frameworks, reinforcing bars. Its excellent weldability makes on-site assembly faster and easier. If you need industrial products with high strength and long-term durability, carbon steel is an economical solution.
Storage Tanks and Pressure Vessels
Certain grades of carbon steel are well-suited for saving liquids and gases. The carbon steel storage tanks of KDM are always applied for storing water, oil, and various industrial fluids. Through surface treatment, carbon steel can possess excellent compressive resistance.
Pipeline Systems
Carbon steel pipes are used for transporting water, steam, gases, and various industrial fluids. They have excellent pressure resistance. In damp or corrosive environments, to extend their service life, coating or lining treatment is carried out. These pipes are especially prevalent in energy, chemical, and infrastructure applications.
Industrial Machinery and Equipment
Carbon steel is applied for manufacturing gears, shafts, frames, and casings because it is easy to process and has stable dimensions. Carbon steel can be good for the long-term operation of equipment. Among them, medium carbon steel can particularly combine strength and toughness perfectly, and is used for mechanical components that bear repeated stress and heavy loads.
Welding and Connection Applications
Low-carbon steel has excellent weldability and is used in equipment assembly. KDM’s carbon steel electrodes are always applied in various structural welding applications, forming stable joints and being easy to operate. Choosing the appropriate electrode for each steel type can provide a secure and high-quality connection.
Automotive and Transport Applications
Carbon steel is used in vehicles for the body, chassis, and safety reinforcement components. Low-carbon steel is easy to shape and can be mass-produced; medium-carbon steel provides strength for axle and suspension components. In railways, carbon steel is used for tracks and wheelsets to withstand long-term load pressure.
Agriculture and Household Hardware
Carbon steel is always applied for agricultural tools and gardening equipment, as well as in bolts and fasteners. In residential and light industrial applications, low-carbon steel is also frequently used for door frames, fences.
FAQ
Does carbon steel tend to rust easily?
Yes. When carbon steel is deprived of air and moisture, it will oxidize, and the surface will gradually develop rust. However, protective methods like galvanization or applying anti-corrosion coatings can greatly delay this process. Moreover, the presence of copper can improve its corrosion resistance.
Is carbon steel safe and non-toxic?
Carbon steel possesses inherent stability and is non-toxic, making it an ideal material for manufacturing food processing equipment and cookware. Compared to some other metals, it does not emit toxic or harmful gases when exposed to high temperatures. However, if it is to be used for a long period, regular rust prevention is necessary.
Is the cost of carbon steel higher than that of alternative materials?
Actually, it is not like that. Carbon steel is made from widely available raw materials and has a mature manufacturing process. Its overall cost is lower than that of alternative materials, such as stainless steel. For large-scale and heavy-duty applications, it is an economical choice.
Is high-carbon steel really more durable?
Yes. The hardness and tensile strength of high-carbon steel are much higher than those of low-carbon steel. Through proper heat treatment, its wear resistance and anti-deformation ability can be further improved. On the downside, it has limited ductility and is more likely to crack when subjected to impact or bending power.
How Does Carbon Steel Compare to Stainless Steel in Harsh Environments?
No. The surface of stainless steel forms a protective film, which can prevent it from being corroded and enable it to operate reliably even in humid, chemical, or salty environments. Carbon steel does not have this self-protection barrier and must rely on additional surface treatment measures.
Is the conductivity of carbon steel better than that of aluminum alloy?
No. Compared with aluminum alloy, carbon steel has slightly weaker electrical and thermal conductivity. Carbon steel is relatively heavy and has poor electrical conductivity, so it is generally not chosen for industrial equipment applications that require high electrical conductivity or high thermal conductivity.
Final thoughts
No matter you are considering using carbon steel for industrial production or daily manufacturing, understanding its characteristics and application scope is an essential step.
KDM is a reliable supplier of carbon steel solutions. We offer a range of high-quality carbon steel products. If you have any needs, please feel free to contact the KDM team. We will provide you with professional advice and technical support.