I. Introduction

Carbon steel plates, as an important member of the steel material family, occupy a pivotal position in the modern industrial system. From towering skyscrapers to ocean-going ships; from precision machinery and equipment to various daily appliances, carbon steel plates are ubiquitous. With their unique properties, diverse classifications, and wide range of applications, they provide a solid material foundation for the development and progress of human society. A thorough understanding of carbon steel plates is crucial for the rational selection and use of this material, and for promoting innovation and development in related industries.

II. Definition and Basic Composition of Carbon Steel Plates

(1) Definition

Carbon steel plate is a ferrous alloy plate with iron as the matrix and carbon as the main alloying element. Its carbon content is usually between 0.0218% and 2.11%, and changes within this range have a significant impact on the properties of the steel plate. In addition, carbon steel plates also contain small amounts of elements such as silicon, manganese, sulfur, and phosphorus, which, although present in relatively small quantities, also play a non-negligible role in regulating the properties of the steel plate.

(2) Basic Constituent Elements and Their Functions

1. Carbon (C): Carbon is the key element affecting the properties of carbon steel plates. As carbon content increases, the strength and hardness of the steel plate increase significantly, but its plasticity and toughness decrease accordingly. For example, low-carbon steel plates (carbon content ≤ 0.25%) have good plasticity and weldability, making them suitable for occasions requiring complex forming processes, such as the manufacture of automobile body panels; while high-carbon steel plates (carbon content > 0.6%) have higher strength and hardness, and are often used for manufacturing wear-resistant parts such as molds and cutting tools.
2. Silicon (Si): Silicon mainly plays a role in deoxidation in carbon steel plates, which can increase the strength and hardness of the steel, but excessive silicon will reduce the plasticity and toughness of the steel. Generally, the silicon content in carbon steel plates is between 0.17% and 0.37%. Within this range, silicon helps to improve the comprehensive performance of the steel plate. For example, in some structural steels, an appropriate amount of silicon can enhance the ability of the steel to resist external deformation.
3. Manganese (Mn): Manganese also has deoxidizing and desulfurizing effects. It can improve the strength and hardenability of steel and improve the hot working performance of steel. In carbon steel plates, the manganese content is usually between 0.35% and 1.20%. For example, in Q345 low-alloy high-strength structural steel, the addition of manganese effectively increases its strength, making it widely used in construction structures, bridges and other fields.
4. Sulfur (S): Sulfur is a harmful element in carbon steel plates. It reduces the hot workability of steel and causes hot brittleness during hot working, leading to cracking. Therefore, in the production of carbon steel plates, the sulfur content needs to be strictly controlled. Generally, the sulfur content in high-quality carbon steel plates does not exceed 0.050%, and in some high-grade high-quality steels, the sulfur content can be as low as 0.015% or less.
5. Phosphorus (P): Phosphorus in steel significantly reduces the plasticity and toughness of the steel, especially in low-temperature environments, a phenomenon known as cold brittleness. At the same time, phosphorus can increase the strength and hardness of steel. In some special cases, such as in the manufacture of shell steel, this property of phosphorus is used to improve certain properties of the steel. However, in most conventional carbon steel plates, the phosphorus content also needs to be strictly controlled, generally not exceeding 0.045%.

III. Classification Methods of Carbon Steel Plates

(1) Classification by Carbon Content

1. Low-carbon steel plates: Low-carbon steel plates have a carbon content ranging from 0.0218% to 0.25%. Due to their low carbon content, they have good plasticity, toughness, and weldability. Their strength is relatively low, but their processing performance is excellent, and they can be made into complex-shaped parts through various forming processes such as stamping and bending. In the automobile manufacturing industry, low-carbon steel plates are widely used in the manufacture of body shells, such as automobile doors and hoods. Using their good formability and weldability can not only ensure the appearance of the body but also ensure welding quality, improving the overall strength and safety of the body. In the construction field, low-carbon steel plates are often used to make thin-walled components of light steel structures. Due to their light weight and good processability, they can effectively reduce the weight of the structure and reduce construction difficulty.
2. Medium-carbon steel plates: Medium-carbon steel plates have a carbon content between 0.25% and 0.6%, with a certain combination of strength, plasticity, and toughness. Compared with low-carbon steel plates, their strength is improved, and they can be used to manufacture mechanical parts that bear medium loads. In the machinery manufacturing industry, medium-carbon steel plates are often used to manufacture shaft parts, such as machine tool spindles and motor shafts. Shaft parts need to bear large torque and bending moments during work. The comprehensive performance of medium-carbon steel plates can meet their strength and toughness requirements. Through appropriate heat treatment processes such as quenching and tempering, their mechanical properties can be further improved to ensure the stable operation of shaft parts under long-term complex working conditions. In building structures, medium-carbon steel plates can be used to manufacture some node connectors with higher strength requirements to ensure the integrity and stability of the structure.
3. High-carbon steel plates: High-carbon steel plates have a carbon content between 0.6% and 2.11%, with high strength and hardness but poor plasticity and toughness. Due to their high hardness and wear resistance, high-carbon steel plates are often used to manufacture parts that need to withstand severe friction and wear. For example, in the field of mold manufacturing, high-carbon steel plates can be used to manufacture stamping dies, forging dies, etc. Molds are in frequent contact with workpieces during work and need to have good wear resistance and deformation resistance. After heat treatment such as quenching and tempering, high-carbon steel plates can meet these performance requirements of molds, extend the service life of molds, and improve production efficiency. In the tool manufacturing industry, such as the manufacture of cutting tools and saw blades, high-carbon steel plates are also commonly used materials. Cutting tools need sharp edges and high hardness to ensure cutting performance, and the characteristics of high-carbon steel plates make them an ideal choice for manufacturing cutting tools.

(2) Classification by Thickness

1. Thin carbon steel plates: Thin carbon steel plates generally have a thickness between 0.2mm and 4mm, with good formability and surface quality. Due to their thin thickness and light weight, they are widely used in fields with high requirements for weight and forming. In the electronics and electrical industry, thin carbon steel plates are often used to manufacture electrical enclosures, such as computer cases and refrigerator casings. Thin carbon steel plates can be made into various complex-shaped and flat-surfaced enclosures through stamping, stretching, and other processes to meet the appearance and structural requirements of electronic and electrical products. At the same time, their light weight is also beneficial to the transportation and installation of products. In the food packaging industry, thin carbon steel plates can be made into food cans after surface treatments such as tin plating and galvanizing, which not only ensures the sealing and corrosion resistance of the packaging but also meets the hygiene requirements of food packaging materials.
2. Medium carbon steel plates: Medium carbon steel plates have a thickness ranging from 4mm to 20mm, with good strength and processing performance. In the construction industry, medium carbon steel plates are often used to manufacture main load-bearing components such as beams and columns of steel structures. Beams and columns play an important role in transmitting and bearing loads in building structures. The strength and thickness of medium carbon steel plates can meet their load-bearing requirements. Through welding, bolt connection, and other methods, medium carbon steel plates can be made into beams and columns of various specifications to build a strong and stable building structure framework. In the machinery manufacturing industry, medium carbon steel plates can be used to manufacture some large mechanical bases, brackets, and other components. These components need to have a certain strength and rigidity to ensure the stability of the machinery during operation, and the performance of medium carbon steel plates can well meet this demand.
3. Thick carbon steel plates: Thick carbon steel plates have a thickness between 20mm and 60mm, with high strength and load-bearing capacity. In the field of shipbuilding, thick carbon steel plates are key materials for manufacturing hull structures, such as hull plates and deck plates. Ships need to withstand seawater corrosion, wind and wave impact, and cargo pressure during navigation. The high strength and thick walls of thick carbon steel plates can ensure the safety and durability of the hull structure and resist harsh marine environments. In the pressure vessel manufacturing industry, thick carbon steel plates are used to manufacture various pressure vessels, such as reactors and storage tanks in the petrochemical industry. Pressure vessels need to withstand harsh working conditions such as high pressure and high temperature. The high strength and good processing performance of thick carbon steel plates can ensure that pressure vessels meet design requirements during manufacturing and operate safely and reliably during use.
4. Extra-thick carbon steel plates: Extra-thick carbon steel plates have a thickness greater than 60mm, with extremely high strength and load-bearing capacity. Due to their complex manufacturing process and high production difficulty, they are usually used in some special fields with extremely high requirements for material performance. In large-scale water conservancy projects, extra-thick carbon steel plates can be used to manufacture sluice gates. The gates need to withstand huge water pressure. The high strength and heavy structure of extra-thick carbon steel plates can ensure that the gates do not deform or damage under long-term water pressure, ensuring the normal operation of water conservancy projects. In nuclear power projects, extra-thick carbon steel plates can be used to manufacture the pressure vessel of nuclear reactors. As a key component of nuclear reactors, the pressure vessel needs to have extremely high strength, sealing, and radiation resistance. After special smelting and processing processes, extra-thick carbon steel plates can meet the strict requirements of nuclear power projects for materials and ensure the safe and stable operation of nuclear power plants.

(3) Classification by Application

1. Structural carbon steel plates: Structural carbon steel plates are mainly used in construction structures, bridge engineering, machinery manufacturing, and other fields as materials for structural parts that bear various loads. In building structures, common grades of carbon steel plates such as Q235 and Q345 are widely used in the construction of house frame structures and industrial plant steel structures. These structural carbon steel plates have good strength and plasticity, which can meet the stress requirements of building structures under different working conditions and ensure the safety and stability of buildings. In bridge engineering, structural carbon steel plates are used to manufacture components such as steel beams and piers of bridges. Bridges need to bear various complex external forces such as vehicle loads, wind loads, and seismic loads. The high performance of structural carbon steel plates can ensure that bridges withstand various tests during long-term use and maintain normal traffic functions. In the field of machinery manufacturing, structural carbon steel plates can be used to manufacture basic structural parts such as the fuselage and frame of large mechanical equipment, providing stable support for the normal operation of mechanical equipment.
2. Carbon steel plates for pressure vessels: Carbon steel plates for pressure vessels are specially used to manufacture various pressure vessels, such as boilers, storage tanks, and reactors. These equipment need to withstand certain pressure and temperature during operation, and have strict requirements on the strength, toughness, welding performance, and corrosion resistance of materials. For example, carbon steel plates used in the manufacture of boilers need to have good high-temperature strength and thermal fatigue resistance to ensure the safe operation of boilers in long-term high-temperature and high-pressure working environments. Carbon steel plates for pressure vessels usually need to undergo strict quality inspection and certification, such as flaw detection and mechanical property testing, to ensure their quality meets relevant standards and specifications and ensure the safe use of pressure vessels.
3. Carbon steel plates for automobiles: Carbon steel plates for automobiles are indispensable materials in the automobile manufacturing process and are widely used in the manufacture of automobile bodies, chassis, engines, and other components. In terms of automobile body manufacturing, the application of high-strength low-alloy carbon steel plates is becoming more and more widespread, such as DP steel (dual-phase steel) and TRIP steel (transformation-induced plasticity steel). These advanced automotive carbon steel plates have high strength, high toughness, and good formability, which can achieve lightweight design of the car body while ensuring the strength and safety of the car body, reducing fuel consumption and exhaust emissions of the car. In the manufacture of automobile chassis, carbon steel plates are used to manufacture components such as frames and axles, which need to have high strength and fatigue resistance to adapt to the complex stresses on the chassis when the car is driving under different road conditions. Some parts in automobile engines, such as crankshafts and connecting rods, are also made of carbon steel plates with specific properties to meet the requirements of high-speed and high-load operation of the engine.
4. Carbon steel plates for shipbuilding: Carbon steel plates for shipbuilding are one of the main materials for building ships and play a crucial role in the performance and safety of ships. Ships sailing in the marine environment need to withstand seawater corrosion, wind and wave impact, and cargo pressure. Therefore, carbon steel plates for shipbuilding need to have high strength, good corrosion resistance, welding performance, and low-temperature toughness. Different specifications and performance of carbon steel plates are selected for different parts of the ship according to their stress conditions and service environment. For example, hull plates need to have high strength and corrosion resistance to resist seawater erosion and wind and wave impact; deck plates need to have good wear resistance and anti-skid performance to ensure the safe walking of personnel on the deck. In order to improve the corrosion resistance of carbon steel plates for shipbuilding, surface treatments such as galvanizing and painting are usually carried out. At the same time, some alloying elements such as nickel and chromium are added during the steel smelting process to improve the corrosion resistance of the steel.

IV. Performance Characteristics of Carbon Steel Plates

(1) Mechanical Properties

1. Strength: The strength of carbon steel plates is closely related to their carbon content, and the strength gradually increases with the increase of carbon content. For example, the yield strength of low-carbon steel plates is generally between 180MPa and 260MPa, and the tensile strength is between 325MPa and 500MPa; the yield strength of medium-carbon steel plates can reach 325MPa to 420MPa, and the tensile strength is between 460MPa and 620MPa; the yield strength of high-carbon steel plates can reach 380MPa to 440MPa, and the tensile strength is between 660MPa and 940MPa. This difference in strength makes carbon steel plates with different carbon contents suitable for engineering fields with different strength requirements. In building structures, for beams, columns, and other components that bear large loads, medium-carbon steel plates or high-carbon steel plates with higher strength are usually selected to ensure the safety and stability of the structure; while in some occasions with relatively low strength requirements but high formability requirements, such as the manufacture of automobile body panels, low-carbon steel plates are selected.
2. Plasticity: Plasticity refers to the ability of a material to undergo permanent deformation without breaking after being stressed. Low-carbon steel plates have good plasticity and can undergo various complex forming processes such as deep drawing and bending without cracking. This characteristic makes low-carbon steel plates widely used in the automobile manufacturing and home appliance manufacturing industries, and can produce product parts with different shapes and exquisite appearances. As the carbon content increases, the plasticity of carbon steel plates gradually decreases. Due to their high hardness and brittleness, high-carbon steel plates have poor plasticity, and process parameters need to be controlled more carefully during processing to avoid defects such as cracks. In the mechanical processing process, for carbon steel plates that need to undergo plastic processing such as forging and rolling, appropriate processing temperatures and deformation amounts need to be selected according to their carbon content and plasticity characteristics to ensure processing quality.
3. Toughness: Toughness is a measure of a material's ability to resist fracture under impact loads. Generally speaking, low-carbon steel plates and medium-carbon steel plates have good toughness and can absorb impact energy to a certain extent to prevent sudden fracture of the material. In some engineering structures that may be subject to impact loads, such as anti-collision facilities of bridges and hooks of cranes, carbon steel plates with good toughness are selected for manufacturing to ensure the safety of the structure under accidental impact. However, due to their high carbon content and relatively complex crystal structure, high-carbon steel plates have relatively poor toughness and are more prone to brittle fracture when impacted. In order to improve the toughness of high-carbon steel plates, appropriate heat treatment processes such as spheroidizing annealing are usually used to improve their microstructure, thereby improving toughness.
4. Hardness: Hardness is the ability of a material to resist local deformation, especially plastic deformation, indentation, or scratch. The hardness of carbon steel plates increases significantly with the increase of carbon content. High-carbon steel plates have high hardness and are suitable for manufacturing parts that need to be wear-resistant, such as molds and cutting tools. In mold manufacturing, high-hardness carbon steel plates can ensure that the surface of the mold does not wear too much due to frequent friction with the workpiece during long-term use, thereby ensuring the accuracy and service life of the mold. Low-carbon steel plates have relatively low hardness and have advantages in some application scenarios where hardness requirements are not high but good formability is required. In actual production, in order to meet different usage requirements, the surface hardness of carbon steel plates can also be adjusted through surface heat treatment and other methods, so that the surface has high hardness and wear resistance, while the interior still maintains good toughness.

(2) Processing Performance

1. Weldability: The weldability of carbon steel plates is closely related to the carbon content. Generally, low-carbon steel plates have good weldability and can achieve reliable connections through various welding methods, such as manual arc welding, carbon dioxide gas shielded welding, and submerged arc welding. In the construction of building steel structures, a large number of low-carbon steel plates are connected into various structural parts through welding processes, and the welding quality directly affects the safety and stability of the structure. The weldability of medium-carbon steel plates is relatively poor. During the welding process, appropriate measures such as preheating, controlling welding current and speed need to be taken to prevent cracks and other defects in the welded joints. Due to their high carbon content, high-carbon steel plates have poor weldability and are difficult to weld. Special welding process design and strict welding process control, such as pre-weld preheating and post-weld heat treatment, are usually required to ensure welding quality. In some important welded structures, such as the welding of pressure vessels, for carbon steel plates with different carbon contents, it is necessary to strictly follow the corresponding welding procedure specifications to ensure that the performance of the welded joints meets the design requirements.
2. Machinability: Machinability refers to the ease with which a material can be cut by a cutting tool. Generally speaking, medium-carbon steel plates have good machinability and can be cut into various shapes and sizes relatively smoothly by cutting tools during mechanical processing. By reasonably selecting tool materials and cutting parameters (such as cutting speed, feed rate, cutting depth, etc.), the cutting efficiency and processing quality of medium-carbon steel plates can be improved. Due to their low hardness, low-carbon steel plates are prone to tool sticking during cutting, which affects the quality of the machined surface. It is necessary to select appropriate cutting fluids and tool geometric parameters to improve machinability. Due to their high hardness, high-carbon steel plates are more difficult to cut. It is necessary to use high-performance tools such as cemented carbide tools and adopt lower cutting speeds and smaller feed rates for processing to ensure the smooth progress of the cutting process and the requirements of processing accuracy. In actual production, for carbon steel plates with different carbon contents, it is necessary to formulate corresponding processing schemes according to their machinability characteristics to improve processing efficiency and reduce processing costs.
3. Formability: Formability refers to the ability of a material to be formed into a desired shape through plastic processing methods (such as stamping, bending, stretching, etc.). Low-carbon steel plates have good formability and can be made into complex-shaped parts through various forming processes without breaking. In the automobile manufacturing industry, a large number of low-carbon steel plates are used to manufacture automobile body panels through stamping processes, such as doors, hoods, and roofs. These panels need to have good appearance quality and dimensional accuracy, and the good formability of low-carbon steel plates can meet this requirement. The formability of medium-carbon steel plates is relatively lower than that of low-carbon steel plates, but they can still be formed through appropriate process measures in some occasions where the forming accuracy requirements are not particularly high. Due to their poor plasticity, high-carbon steel plates are more difficult to form. When performing forming processing, it is necessary to more strictly control processing parameters such as heating temperature and deformation rate to prevent defects such as cracks in the material during forming. In some special forming processes, such as hot forming, high-carbon steel plates can be heated to improve their plasticity, thereby achieving the forming of complex shapes.