Q355B carbon steel
Q355B Carbon Steel
Q355B is a widely used low-alloy high-strength structural steel known for its excellent mechanical properties, weldability, and versatility in engineering applications. It belongs to China’s GB/T standard series and is designed for structural components requiring higher strength than ordinary carbon steels (e.g., Q235), making it a staple in construction, machinery, and automotive industries.
Basic Information
Definition: Q355B is a low-alloy steel (with alloying elements like manganese, silicon, and trace amounts of niobium, vanadium, or titanium) that achieves high strength through solid solution strengthening and grain refinement. The “B” in its designation indicates it meets impact toughness requirements at 20°C, ensuring reliability in moderate-temperature environments.
Corresponding Standards: Conforms to GB/T 1591-2018 (Low-alloy high-strength structural steels). It is equivalent to international grades such as:
European: S355JR (EN 10025-2)
American: ASTM A572 Grade 50
Japanese: JIS SM490B
Key Characteristics: High yield strength, good toughness, excellent weldability, and cost-effectiveness, making it suitable for load-bearing structural components.
Chemical Composition
Q355B’s composition is balanced to optimize strength, toughness, and weldability, with controlled alloying elements:
Element Content Range Role in the Steel
Carbon (C) ≤0.20% Provides strength while keeping weldability intact (low carbon avoids brittle welds).
Manganese (Mn) 1.00–1.60% Primary strengthening element; enhances toughness and hardenability.
Silicon (Si) ≤0.55% Acts as a deoxidizer; improves strength and oxidation resistance.
Phosphorus (P) ≤0.035% Strictly controlled to prevent brittleness, especially in welded joints.
Sulfur (S) ≤0.035% Minimized to avoid hot cracking during welding and reduce toughness loss.
Niobium (Nb) 0.015–0.060% Refines grain structure, improving strength and toughness.
Vanadium (V) 0.02–0.15% Enhances strength through grain refinement and precipitation hardening.
Titanium (Ti) 0.02–0.20% Refines grains and prevents excessive grain growth during heat treatment.
Iron (Fe) Balance Base metal providing structural integrity.
Physical Properties
Density: ~7.85 g/cm³ (consistent with most carbon and low-alloy steels).
Melting Point: ~1430–1450°C.
Thermal Conductivity: ~45 W/(m·K) at room temperature.
Coefficient of Thermal Expansion: ~12×10⁻⁶/°C (20–100°C), suitable for structural stability in temperature fluctuations.
Elastic Modulus: ~206 GPa, ensuring rigidity in load-bearing applications.
Mechanical Properties
Q355B’s mechanical properties are defined by its high strength and good toughness, critical for structural safety:
Property Minimum Requirement (Hot-Rolled State)
Yield Strength (Rp0.2) ≥355 MPa (hence the designation “Q355”)
Tensile Strength (Rm) 470–630 MPa
Elongation (A) ≥21%
Impact Toughness (Akv) ≥34 J (at 20°C, V-notch test)
Hardness ~140–180 HB
Toughness: The “B” grade ensures it retains sufficient impact resistance at 20°C, making it suitable for outdoor and industrial environments.
Fatigue Resistance: Good for cyclic load applications (e.g., bridges, machinery frames) due to its balanced strength and ductility.
Welded Joint Performance: Welds retain ~80–90% of the base metal’s strength when proper welding procedures are used.
Heat Treatment
Q355B is typically used in the hot-rolled or normalized state and does not require additional heat treatment for most applications:
Normalizing: Optional for large sections to refine grain structure and improve uniformity. Process: Heat to 880–920°C, hold, then air cool.
Welding Heat Treatment: Post-weld annealing may be used for thick sections to reduce residual stresses, but it is not mandatory for most structural uses.
Processing Performance
Weldability: Excellent—compatible with common welding methods (arc welding, gas welding, resistance welding). Low carbon and controlled impurities minimize the risk of cold cracking. Preheating is generally not required for thin sections (<25mm). Formability: Good for cold and hot forming processes, including bending, rolling, and punching. Its ductility allows for complex shapes in structural components (e.g., beams, pipes). Machinability: Suitable for standard machining operations (turning, milling, drilling) using high-speed steel or carbide tools. Its strength requires proper tool selection to avoid excessive wear. Cutting: Easily cut with plasma, laser, or oxy-fuel methods, producing clean edges suitable for structural assembly. Application Fields Q355B is the material of choice for load-bearing structural components across industries: Construction Engineering: Bridges, building frames, and steel structures (columns, beams, trusses). High-rise buildings and industrial plants requiring high strength-to-weight ratios. Mechanical Manufacturing: Machinery frames, equipment bases, and structural parts for heavy machinery. Crane booms, hydraulic supports, and pressure vessel shells (non-critical pressure applications). Automotive & Transportation: Truck frames, trailer chassis, and bus structural components. Railway vehicle underframes and cargo containers. Energy & Infrastructure: Oil and gas pipelines, power plant structures, and wind turbine towers. Transmission towers and communication masts. Advantages and Limitations Advantages High Strength-to-Cost Ratio: Offers 50% higher yield strength than Q235 at a moderate price premium. Versatility: Suitable for diverse applications from construction to machinery. Easy Fabrication: Welds and forms well, reducing manufacturing complexity. Reliability: Consistent performance in ambient and moderate-temperature environments. Limitations Corrosion Resistance: Poor in humid or corrosive environments; requires protective coatings (painting, galvanizing) for outdoor use. High-Temperature Performance: Not suitable for sustained use above 300°C, as strength decreases significantly. Thick Section Limitations: Very thick plates (>100mm) may require controlled rolling or normalizing to ensure uniform properties.
In summary, Q355B is a reliable low-alloy high-strength steel that balances performance, cost, and fabricability, making it indispensable in modern structural engineering and manufacturing. Its widespread adoption underscores its role as a workhorse material for load-bearing applications.
SS400 steel
SS400 Steel
SS400 is a widely used general structural carbon steel defined by Japanese industrial standards (JIS). It is known for its balanced mechanical properties, excellent weldability, and cost-effectiveness, making it a staple in construction, machinery, and manufacturing industries globally.
Basic Information
Definition: SS400 is a non-alloy carbon steel designed for structural applications where moderate strength and ductility are required. The “SS” stands for “Structural Steel,” and “400” refers to its minimum tensile strength of 400 MPa (in the JIS standard).
Corresponding Standards: Conforms to JIS G3101-2015 (Rolled steels for general structure). It is equivalent to international grades such as:
Chinese: Q235B (GB/T 700)
European: S235JR (EN 10025-2)
American: ASTM A36
Indian: Fe410WA (IS 2062)
Key Characteristics: Good formability, weldability, and machinability, with sufficient strength for general structural loads.
Chemical Composition
SS400’s composition is simple, with minimal alloying elements, focusing on carbon and manganese for basic strength:
Element Content Range Role in the Steel
Carbon (C) ≤0.22% Provides basic strength; kept low to ensure weldability and avoid brittleness.
Manganese (Mn) 0.30–1.60% Enhances strength and ductility; aids in deoxidation during production.
Silicon (Si) ≤0.35% Acts as a deoxidizer; improves strength and oxidation resistance slightly.
Phosphorus (P) ≤0.050% Controlled to prevent cold brittleness, especially in welded joints.
Sulfur (S) ≤0.050% Minimized to avoid hot cracking during rolling or welding.
Iron (Fe) Balance Base metal providing structural integrity.
Physical Properties
Density: ~7.85 g/cm³ (standard for carbon steels).
Melting Point: ~1430–1450°C.
Thermal Conductivity: ~45 W/(m·K) at room temperature.
Coefficient of Thermal Expansion: ~12×10⁻⁶/°C (20–100°C), ensuring stability in temperature fluctuations.
Elastic Modulus: ~206 GPa, providing rigidity in structural applications.
Mechanical Properties
SS400’s mechanical properties are tailored for general structural use, emphasizing ductility and workability:
Property Minimum Requirement (Hot-Rolled State)
Yield Strength (Rp0.2) ≥235 MPa (for thickness ≤16mm)
Tensile Strength (Rm) 400–510 MPa
Elongation (A) ≥25% (for thickness ≤16mm)
Impact Toughness Not specified in JIS G3101 (focus on general structural use, not low-temperature toughness).
Hardness ~110–160 HB
Ductility: High elongation ensures the steel can deform under load without fracturing, critical for structural safety.
Strength Variation: Yield strength decreases slightly with increasing thickness (e.g., ~215 MPa for 16–40mm thickness).
Heat Treatment
SS400 is typically used in the hot-rolled state and does not require additional heat treatment for most applications:
Hot Rolling: The primary production process, which refines the grain structure and imparts the desired mechanical properties.
Normalizing: Optional for large sections to improve uniformity, but rarely needed due to the steel’s low carbon content.
Processing Performance
Weldability: Excellent—compatible with all common welding methods (arc welding, gas welding, resistance welding). Low carbon content minimizes the risk of weld cracking, and preheating is generally unnecessary for thin sections.
Formability: Good for cold and hot forming processes, including bending, rolling, stamping, and punching. Its ductility allows for complex shapes in structural components.
Machinability: Easy to machine with standard tools (high-speed steel or carbide). Low carbon content reduces tool wear, making it cost-effective for machining operations.
Cutting: Easily cut with plasma, laser, oxy-fuel, or shearing methods, producing clean edges suitable for assembly.
Application Fields
SS400 is widely used in general structural and manufacturing applications due to its versatility:
Construction Engineering:
Building frames, beams, columns, and trusses for residential and industrial buildings.
Bridges, scaffolding, and temporary structures.
Reinforcement bars and steel plates for concrete structures.
Mechanical Manufacturing:
Machinery frames, equipment bases, and brackets.
Pipes, tubes, and fittings for non-high-pressure applications.
Automotive parts (e.g., chassis components, brackets) and agricultural machinery.
Fabrication & Metal Products:
Steel sheets for roofing, siding, and containers.
Fasteners (bolts, nuts) and general-purpose metal parts.
Storage tanks, drums, and simple pressure vessels (non-critical use).
Infrastructure:
Street furniture (signposts, guardrails) and railway components.
Shipping containers and logistics equipment.
Advantages and Limitations
Advantages
Cost-Effective: Lower production costs compared to alloy steels, making it ideal for large-scale structural projects.
Easy Fabrication: Excellent weldability, formability, and machinability reduce manufacturing complexity and costs.
Versatility: Suitable for a wide range of applications from construction to consumer goods.
Reliability: Consistent performance in ambient temperature environments for non-critical structural loads.
Limitations
Limited Strength: Lower yield strength than high-strength low-alloy steels (e.g., Q355B or S355JR), so it may require thicker sections for heavy loads.
Poor Corrosion Resistance: Susceptible to rust in humid or corrosive environments; requires protective coatings (painting, galvanizing) for outdoor use.
Low-Temperature Toughness: Not designed for extreme cold (no specified impact toughness at sub-zero temperatures), limiting use in cold regions without modifications.
High-Temperature Limitation: Strength decreases significantly above 300°C, making it unsuitable for high-temperature applications.
Comparison with Similar Steels
SS400 is often compared to other general structural steels:
Steel Grade Standard Yield Strength (Min) Tensile Strength Range Key Use Case
SS400 JIS G3101 235 MPa (≤16mm) 400–510 MPa General construction, low-load structures.
Q235B GB/T 700 235 MPa (≤16mm) 375–500 MPa Chinese equivalent for structural use.
ASTM A36 ASTM A36 250 MPa 400–550 MPa North American counterpart, similar properties.
S235JR EN 10025-2 235 MPa (≤16mm) 360–510 MPa European equivalent with better impact toughness.
In summary, SS400 is a reliable, economical structural steel that excels in general-purpose applications where moderate strength and ease of fabrication are prioritized. Its widespread use across industries reflects its role as a foundational material in modern construction and manufacturing.