What Is Q235 Steel ？

 

Q235 steel is a low-carbon structural steel commonly used in China for various industrial applications. It is valued for its balance of strength and flexibility, making it useful for mechanical manufacturing and construction.

Q235 Steel Grades and Composition

Q235 steel has four main grades: Q235A, Q235B, Q235C, and Q235D. These grades differ in their chemical makeup and impact resistance:

• Q235A:

  • Carbon (C) ≤ 0.22%
  • Silicon (Si) ≤ 0.35%
  • Manganese (Mn) ≤ 1.40%
  • Phosphorus (P) ≤ 0.045%
  • Sulfur (S) ≤ 0.050%

• Q235B:

  • Carbon (C) ≤ 0.20% (up to 0.22% by agreement)
  • Silicon (Si) ≤ 0.35%
  • Manganese (Mn) ≤ 1.40%
  • Phosphorus (P) ≤ 0.045%
  • Sulfur (S) ≤ 0.045%

• Q235C:

  • Carbon (C) ≤ 0.17%
  • Silicon (Si) ≤ 0.35%
  • Manganese (Mn) ≤ 1.40%
  • Phosphorus (P) ≤ 0.040%
  • Sulfur (S) ≤ 0.040%

• Q235D:

  • Carbon (C) ≤ 0.17%
  • Silicon (Si) ≤ 0.35%
  • Manganese (Mn) ≤ 1.40%
  • Phosphorus (P) ≤ 0.035%
  • Sulfur (S) ≤ 0.035%

Mechanical Properties of Q235 Steel

• Density: 7.85 g/cm³.

• Yield Strength:

  • 235 MPa for bars or plates with a diameter ≤ 16 mm.
  • Decreases as thickness increases: 225 MPa for 16 < d ≤ 40 mm, 215 MPa for 40 < d ≤ 100 mm, 195 MPa for 100 < d ≤ 150 mm, 185 MPa for 150 < d ≤ 200 mm.

• Tensile Strength: 370-500 MPa for bars or plates ≤ 100 mm in diameter.

Impact Energy for Different Grades

• Q235B: 27 J at +20°C.
• Q235C: Impact energy tested at 0°C.
• Q235D: Impact energy tested at -20°C.

Common Uses of Q235 Steel

Q235 steel is widely used due to its reliable mechanical properties:

• Construction and Engineering: Building structures, transmission towers, bridges, and factory buildings.
• Mechanical Manufacturing: Ideal for parts like bearings and gears.
• Automobile Manufacturing: Used in car frames, wheels, and axles.
• Other Applications: Boilers, containers, screws, nuts, brackets, and stands.

Forms of Q235 Steel

Q235 steel is available in various forms like plates, round bars, square bars, flat bars, angles, channels, I-beams, and steel pipes.

Equivalent Steel Grades in Other Countries

• ASTM A36 in the United States.
• S235JR in Europe.
• E250 in India.

Origin and Standards

Q235 steel is made according to the GB/T700 standard, a widely recognized Chinese national standard. This standard defines the chemical composition, mechanical properties, and production processes for Q235 steel, ensuring it meets performance needs in construction and manufacturing.

Production Process

Producing Q235 steel involves several key steps: 1. Selecting raw materials: High-quality iron ore, carbon (from coal or coke), and limestone are chosen. 2. Melting: These materials are melted in a blast furnace to create molten iron. 3. Refining: The molten iron is refined in a basic oxygen furnace (BOF) or an electric arc furnace (EAF) to remove impurities. 4. Adding alloying elements: Silicon, manganese, phosphorus, and sulfur are added to meet the GB/T700 standard’s chemical requirements. 5. Casting and rolling: The molten steel is cast into ingots, slabs, or billets and undergoes hot rolling to achieve the final shape.

Chemical Composition

Q235 steel’s chemical makeup is tightly controlled under the GB/T700 standard to maintain quality. The key components include: – Carbon (C): 0.14-0.22% – Silicon (Si): ≤0.35% – Manganese (Mn): 0.30-0.70% – Phosphorus (P): ≤0.045% – Sulfur (S): ≤0.045%

Grades of Q235 Steel

Q235 steel comes in four grades—Q235A, Q235B, Q235C, and Q235D—each with varying chemical and mechanical properties: – Q235A: Carbon ≤0.22%, Silicon ≤0.35%, Manganese ≤1.4%, Phosphorus ≤0.045%, Sulfur ≤0.05% – Q235B: Carbon ≤0.2%, Silicon ≤0.35%, Manganese ≤1.4%, Phosphorus ≤0.045%, Sulfur ≤0.045% – Q235C: Carbon ≤0.17%, Silicon ≤0.35%, Manganese ≤1.4%, Phosphorus ≤0.04%, Sulfur ≤0.04% – Q235D: Carbon ≤0.17%, Silicon ≤0.35%, Manganese ≤1.4%, Phosphorus ≤0.035%, Sulfur ≤0.035%

Chemical Composition of Q235 Steel

Q235 steel mainly contains carbon (C), silicon (Si), manganese (Mn), phosphorus (P), and sulfur (S). The concentration of these elements varies based on the specific grade of Q235 steel.

Chemical Elements by Grade

| Steel Grade | Carbon % (≤) | Silicon % (≤) | Manganese % (≤) | Phosphorus % (≤) | Sulfur % (≤) | |————-|—————|—————|—————–|—————–|————–| | Q235A | 0.22 | 0.35 | 1.4 | 0.045 | 0.05 | | Q235B | 0.20 | 0.35 | 1.4 | 0.045 | 0.045 | | | 0.22 (by agreement) | | | | | | Q235C | 0.17 | 0.35 | 1.4 | 0.04 | 0.04 | | Q235D | 0.17 | 0.35 | 1.4 | 0.035 | 0.035 |

Deoxidation Method

• Q235A and Q235B: Rimmed or Killed
• Q235C: Killed
• Q235D: Fully Killed

As you move from Q235A to Q235D, the levels of sulfur and phosphorus decrease, making the steel purer and of higher quality. The chemical composition of Q235 steel complies with China’s national standard GB/T 700.

Mechanical Properties of Q235 Steel

Yield Strength

• Yield strength varies by thickness:
  • Thickness ≤16 mm: ≥235 MPa
  • Thickness 16-40 mm: ≥225 MPa
  • Thickness 40-60 mm: ≥215 MPa
  • Thickness 60-100 mm: ≥215 MPa
  • Thickness 100-150 mm: ≥195 MPa
  • Thickness 150-200 mm: ≥185 MPa

Tensile Strength

• Tensile strength ranges from 370 to 500 MPa.

Elongation

• Elongation at break is around 26%.

Impact Toughness

• Impact toughness is typically ≥ 27 J, providing good resistance to sudden impacts.

Hardness

• Hardness is measured at ≤ 201 on a cone hardness tester.

Density

• Density is 7.85 g/cm³.

Melting Point

• The melting point is between 1420-1460°C.

Thermal Conductivity

• Thermal conductivity is 51.9 W/(m·K).

Coefficient of Linear Expansion

• At 20°C, the coefficient of linear expansion is 11.7 µm/m·K.

Physical Properties of Q235 Steel

Q235 steel is known for its well-balanced physical properties, making it suitable for a wide range of applications in construction and industrial machinery. Here are its key characteristics:

• Density: About 7.85 g/cm³, making it relatively lightweight compared to other metals.

• Melting Point: The melting point is around 1493°C, but it can vary slightly between 1420-1460°C depending on the source.

• Specific Heat Capacity: At 20°C, the specific heat capacity is 470 J/(Kg·K), allowing efficient heat management during welding and machining.

• Electrical Resistivity: The electrical resistivity is approximately 0.15 μΩ·m at 20°C, making it conductive enough for many electrical and mechanical systems.

• Elastic Modulus (Young’s Modulus): With an elastic modulus of 200 GPa (or kN/mm²), Q235 steel has high stiffness, helping it resist elastic deformation under stress.

• Thermal Conductivity: Its thermal conductivity ranges between 49-53 W/m·K when measured from 0-100°C, ensuring efficient heat dissipation in high-temperature environments.

• Coefficient of Thermal Expansion: The coefficient of thermal expansion is between 11.3-11.6 × 10^-6/K at 20°C, describing how the steel expands when heated.

• Poisson’s Ratio: Q235 steel has a Poisson’s ratio of 0.24-0.28, which indicates how much it will contract or expand in directions perpendicular to an applied force.

Characteristics of Q235 Steel

Q235 steel has several features that make it suitable for many structural and manufacturing uses. These properties improve its performance in construction, fabrication, and machining.

Weldability

• Q235 steel welds easily with methods like arc welding, resistance welding, and gas welding.
• It forms strong and reliable welds, making it efficient for fabrication and construction.

Machinability

• Q235 steel is highly machinable, suitable for common processes like cutting, drilling, and milling.
• Its low carbon content (less than 0.22%) reduces brittleness, improving its workability.

Ductility and Toughness

• Q235 steel has good ductility, allowing it to undergo plastic deformation without breaking. Depending on its thickness, it has an elongation of 20-26%.
• It also has strong toughness, helping it absorb energy and resist fracture under impact or dynamic loads.

Formability

• Q235 steel is highly formable, making it easy to shape, bend, and form during manufacturing.
• Its low carbon content allows it to be shaped without becoming brittle.

Additional Properties

• Density: About 7.85 g/cm³.
• Melting Point: 1420-1460°C.
• Tensile Strength: 370-500 MPa.
• Yield Strength: Minimum yield strength of 235 MPa.
• Hardness: Around 100-130 HB, offering good machinability and enough wear resistance for most applications.

Applications of Q235 Steel

Building and Construction

• Building Structures: Q235 steel is widely used for frames, beams, and columns in buildings. Its high strength and ductility ensure the stability and reliability of structures.
• Bridges: Q235 is a top choice for bridge construction due to its strong mechanical properties and weldability.
• Structural Components: It is often used in beams, columns, trusses, and brackets in construction projects.
• High-Voltage Transmission Towers: The steel’s durability makes it ideal for high-voltage transmission towers, which must endure tough environmental conditions.
• Boiler Manufacturing: Q235 steel’s balanced properties and good weldability make it a solid option for boiler manufacturing, ensuring safety and longevity.

Machinery and Equipment

• Machinery Parts: Q235 steel is commonly used in machine frames, connecting rods, bearings, and gears. Its strength and machinability boost the durability and performance of machinery.
• General Fabrication: Due to its weldability and ease of processing, Q235 is a go-to material in general machinery fabrication.

Automotive Industry

• Car Body Frames: Q235 steel is widely used in car body frames, wheels, and axles, providing strength and safety to vehicles.
• Chassis Components: It is used in chassis, engines, suspension, and transmission parts, contributing to the durability and performance of automobiles.

Pipelines and Welded Structures

• Pipelines: Q235 steel is ideal for pipelines due to its structural strength and excellent weldability, ensuring safe and efficient material transport.
• Containers and Cargo Ships: Its strength and durability make Q235 suitable for containers, railcars, and cargo ships, which need to handle heavy loads.
• Welded Structures: Q235 is a popular choice for welded structures like scaffolding, purlins, and roofing, providing stability and long-lasting support.

Railway and Industrial Applications

• Railway Tracks: The high strength and ductility of Q235 steel make it reliable for railway tracks, supporting the safety and durability of rail infrastructure.
• Metal Furniture: Q235 is used in metal furniture frames, shelving, and storage racks, offering sturdy solutions for industrial storage needs.

Grades of Q235 Steel

 

Q235 steel has four main grades: Q235A, Q235B, Q235C, and Q235D. These grades differ in chemical composition, mechanical properties, and the impact temperatures they can withstand. Here’s an overview of each grade:

Chemical Composition

• Q235A:

  • Carbon (C) ≤ 0.22%
  • Manganese (Mn) ≤ 1.4%
  • Silicon (Si) ≤ 0.35%
  • Sulfur (S) ≤ 0.050%
  • Phosphorus (P) ≤ 0.045%

• Q235B:

  • Carbon (C) ≤ 0.20%
  • Manganese (Mn) ≤ 1.4%
  • Silicon (Si) ≤ 0.35%
  • Sulfur (S) ≤ 0.045%
  • Phosphorus (P) ≤ 0.045%

• Q235C:

  • Carbon (C) ≤ 0.17%
  • Manganese (Mn) ≤ 1.4%
  • Silicon (Si) ≤ 0.35%
  • Sulfur (S) ≤ 0.040%
  • Phosphorus (P) ≤ 0.040%

• Q235D:

  • Carbon (C) ≤ 0.17%
  • Manganese (Mn) ≤ 1.4%
  • Silicon (Si) ≤ 0.35%
  • Sulfur (S) ≤ 0.035%
  • Phosphorus (P) ≤ 0.035%

Mechanical Properties

• Tensile Strength: 370-500 MPa for all grades
• Yield Strength: 235 MPa for all grades
• Elongation: Around 26% for all grades

Impact Resistance

The grades vary mainly in the temperatures they can handle during impact tests:

• Q235A: No impact test required
• Q235B: Impact test at 20°C
• Q235C: Impact test at 0°C
• Q235D: Impact test at -20°C
• Q235E: Impact test at -40°C (Q235E is less common)

Applications by Grade

• Q235A: Suitable for general construction and engineering, such as buildings and bridges.
• Q235B: Common in structural applications, including beams and columns.
• Q235C: Used in manufacturing, especially in automotive and machinery industries.
• Q235D: Ideal for environments that need greater strength and durability, such as high-strength components.

Equivalence

Q235 steel has various international equivalents across standards, making it widely applicable in different regions. The equivalence of Q235 steel is divided into different grades (A, B, C, D), each aligning with different international standards based on composition and mechanical properties.

Q235A Equivalence

• ASTM A36/A283M Grade D (USA)
• Ust37-2, RSt37-2 (German DIN)
• SS440, SM400A (Japanese JIS G3101) – Yield strength: 245 MPa
• 080A15 (British BS 970) – Yield strength: 235 MPa
• E235B (European EN 10025-2) – Yield strength: 235 MPa

Q235B Equivalence

• ASTM A36/A283M Grade D (USA)
• S235JR, S235JRG1, S235JRG2 (European EN 10025-2) – Yield strength: 235 MPa
• SS440, SM400A (Japanese JIS G3101) – Yield strength: 245 MPa
• 080A15 (British BS 970)
• E235B (European EN 10025-2) – Yield strength: 235 MPa

Q235C Equivalence

• ASTM A36/A283M Grade D and Grade 65 (USA)
• S235JO (European EN 10025-2) – Yield strength: 235 MPa
• SM400A, SM400B (Japanese JIS G3106) – Yield strength: 245 MPa
• 080A15 (British BS 970)
• E235C (European EN 10025-2) – Yield strength: 235 MPa

Q235D Equivalence

• ASTM A36/A283M Grade D (USA)
• S235J2G3, S235J2G4 (European EN 10025-2) – Yield strength: 235 MPa
• SM400A (Japanese JIS G3106) – Yield strength: 245 MPa
• E235D (European EN 10025-2) – Yield strength: 235 MPa

Each Q235 steel grade meets the requirements of different conditions, with varied yield strengths and equivalents suited to specific global standards.