Q460D is a specific grade of high-strength structural steel defined by the European standard EN 10025-6: Hot rolled products of structural steels - Part 6: Technical delivery conditions for flat products of high yield strength structural steels in the quenched and tempered condition.
Here are its key properties:
Designation Meaning:
Q: Stands for "Yield Strength" (Querkraft in German).
460: Indicates the minimum specified yield strength (ReH) at room temperature (≤ 16mm thickness) is 460 Megapascals (MPa).
D: Indicates the toughness grade, specifically the Charpy V-notch impact energy requirement at -20°C.
Key Mechanical Properties:
Yield Strength (ReH): Minimum 460 MPa (for nominal thickness ≤ 16mm). Yield strength decreases slightly as the plate thickness increases.
Tensile Strength (Rm): Typically between 570 MPa to 720 MPa.
Elongation at Break (A): Minimum 17% (for thickness ≤ 40mm, measured on a proportional gauge length Lo = 5.65√So). This indicates good ductility.
Impact Toughness (KV): The "D" grade requires a minimum average Charpy V-notch impact energy of 27 Joules (J) at a test temperature of -20°C. This is its most defining characteristic, signifying excellent resistance to brittle fracture at low temperatures.
Chemical Composition (Typical Ranges - Exact limits depend on thickness & producer):
Carbon (C): Low, typically ≤ 0.20%. This helps with weldability.
Manganese (Mn): Higher levels (e.g., 1.00 - 1.70%) contribute significantly to strength and hardenability.
Silicon (Si): Used for deoxidation and some strengthening.
Phosphorus (P) & Sulfur (S): Kept very low (e.g., P ≤ 0.025%, S ≤ 0.015%) to improve toughness and weldability.
Microalloying Elements: Often contains additions like:
Niobium (Nb): Primary grain refiner and precipitation strengthener.
Vanadium (V): Precipitation strengthener.
Titanium (Ti): Grain refiner and nitride former.
Aluminum (Al): Used for deoxidation and grain refinement.
Other Elements: May contain small amounts of Nickel (Ni), Chromium (Cr), Molybdenum (Mo), Copper (Cu), Boron (B), or Nitrogen (N) for specific property enhancements.
Processing & Condition:
Quenched and Tempered (Q+T): This is the mandatory heat treatment condition for Q460D. The steel is heated, rapidly cooled (quenched), and then reheated to a specific lower temperature (tempered). This process achieves the high strength combined with the required toughness and ductility.
Key Characteristics:
High Strength: Significantly stronger than common structural steels like S355, allowing for lighter structures or higher load-bearing capacity.
Excellent Low-Temperature Toughness: The "D" grade ensures reliable performance down to -20°C, making it suitable for structures in cold climates or subjected to dynamic/impact loads.
Good Weldability: The low carbon content and controlled chemistry generally make it weldable using common processes (SMAW, GMAW, FCAW, SAW). However, strict adherence to qualified welding procedures (preheat, interpass temp, consumable selection) is crucial due to the high strength and Q+T condition.
Good Ductility: Adequate elongation allows for some deformation before failure, important for seismic resistance and structural integrity.
Typical Applications:
Critical structural components requiring high strength and toughness.
Bridges (especially in cold regions).
High-rise buildings.
Crane structures and lifting equipment.
Offshore structures (parts not requiring direct seawater corrosion resistance).
Mining equipment.
Components subjected to heavy loads, dynamic stresses, or low temperatures.
Important Considerations:
Thickness Effect: Yield and tensile strength values decrease as the plate/section thickness increases. Always refer to the specific material certificate for the properties of the actual thickness being used.
Weldability: While generally good, welding Q460D requires careful procedure selection and control to avoid issues like hydrogen cracking (cold cracking) or softening in the heat-affected zone (HAZ). Preheating is almost always required.
Corrosion Resistance: Like most carbon steels, Q460D is not inherently corrosion resistant. Protective coatings (painting, galvanizing) are necessary for exposed environments.
CE Marking: Q460D products supplied under EN 10025-6 are CE marked, indicating conformity with EU regulations for construction products.
In summary, Q460D is a high-strength quenched and tempered structural steel characterized by a minimum yield strength of 460 MPa and excellent impact toughness down to -20°C, making it ideal for demanding structural applications where weight savings, high load capacity, and performance in colder conditions are critical.
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