GB/T 3094 Q660 High Strength Cold
GB/T 3094 Q660 High Strength Cold-Drawn Square & Rectangular Hollow Section Pipe Data
Technical data for Q660 square and rectangular hollow sections manufactured according to GB/T 3094 standard. Includes chemical composition, mechanical properties, and international equivalent grades.
Cold-Drawing, subsequent appropriate processes include cutting, machining, welding (requires preheating and post-weld heat treatment per qualified procedures), and hot-dip galvanizing.
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GB/T 3094 Q660 High Strength Cold Introduction
Q660 is a high-strength low-alloy structural steel grade specifically processed into cold-drawn square (SHS) and rectangular (RHS) hollow sections as defined by the Chinese national standard GB/T 3094. This standard governs cold-drawn shaped steel tubes for structural applications. With a minimum specified yield strength of 660 MPa, Q660 offers an exceptional strength-to-weight ratio, enabling lighter structures and reduced material consumption in demanding engineering projects. The cold-drawing process enhances dimensional accuracy, surface finish, and mechanical properties through work hardening. Key characteristics include high yield and tensile strength, good weldability with appropriate procedures, and moderate toughness. It is primarily supplied in a high-strength as-drawn condition, suitable for heavy-duty structural frameworks, machinery, and transportation equipment where high load-bearing capacity is critical.
GB/T 3094 Q660 High Strength Cold Chemical Composition
The chemical composition for Q660 grade is generally based on requirements for high-strength structural steels. The following table provides reference values as per the typical chemistry for a Q660 grade in accordance with the principles of GB/T 1591 for high-strength low-alloy steels, which is the base material standard for mechanical properties referenced by GB/T 3094. Composition is designed to achieve high strength through microalloying and controlled grain refinement.
| Element | Standard Value (wt%) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.12 | Key strength element, kept low for weldability |
| Silicon (Si) | ≤ 0.50 | Deoxidizer and strength enhancer |
| Manganese (Mn) | ≤ 2.00 | Crucial for strength and hardenability |
| Phosphorus (P) | ≤ 0.025 | Controlled for ductility and toughness |
| Sulfur (S) | ≤ 0.015 | Controlled for ductility and toughness |
| Niobium (Nb) | ≤ 0.10 | Microalloying element for grain refinement and precipitation strengthening |
| Vanadium (V) | ≤ 0.12 | Microalloying element for precipitation strengthening |
| Titanium (Ti) | ≤ 0.10 | Microalloying element for grain refinement, often combined with Nb/V |
| Aluminum (Al) | ≥ 0.015 (total) | Grain refining element |
| Molybdenum (Mo) | ≤ 0.50 | Increases strength and hardenability (optional in some formulations) |
| Boron (B) | ≤ 0.0050 | Enhances hardenability in some low-carbon variants of Q660 grades |
GB/T 3094 Q660 High Strength Cold Thermal and Electrical Physical Properties
Physical properties are typical for low-alloy high-strength steels with similar chemical composition. These values are for general engineering calculations and may vary slightly based on exact chemistry and processing history. They are valid at ambient temperatures unless a temperature range is specified. Electrical resistivity is important for calculating resistance in structural members.
| Property | Standard Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | ~ 7.83 | g/cm³ | At 20 °C |
| Elastic Modulus (E) | 205 | GPa | At 20 °C, longitudinal direction |
| Shear Modulus (G) | ~ 80 | GPa | At 20 °C, calculated from E and ν |
| Poisson's Ratio (ν) | 0.29 | — | At 20 °C |
| Thermal Expansion Coeff. (α) | 11.5 | 10⁻⁶/K | Average value for 20-100 °C |
| Thermal Expansion Coeff. (α) | 13.3 | 10⁻⁶/K | Average value for 20-300 °C |
| Thermal Conductivity (λ) | ~ 38 | W/(m·K) | At 20 °C, typical value for similar HSLA steel |
| Specific Heat Capacity | ~ 475 | J/(kg·K) | At 20 °C, typical value for similar HSLA steel |
| Electrical Resistivity (ρ_e) | ~ 0.25 | μΩ·m | At 20 °C, typical value for similar HSLA steel |
GB/T 3094 Q660 High Strength Cold Mechanical Properties
Mechanical properties for cold-drawn Q660 hollow sections are defined by the base material standard for the specified grade, as cold-drawing significantly increases strength but reduces ductility from the hot-rolled condition. Values presented are for the as-delivered cold-drawn (+C) condition and represent minimum requirements unless stated otherwise. Testing is performed on longitudinal strip specimens taken from the finished tube body. Property requirements may be agreed upon between the purchaser and the manufacturer due to variations in section size, wall thickness, and drawing reduction.
| Property | Standard Requirement Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | Min. 660 | MPa | Room temperature, as-drawn (+C) condition |
| Tensile Strength (Rm) | 720 ~ 900 | MPa | Room temperature, as-drawn (+C) condition |
| Elongation (A) | Min. 12 | % | Room temperature, gauge length L0 = 5.65√S0 for longitudinal strip specimen |
| Elongation (A) | Min. 16 | % | Alternate agreement value for +SR condition or specific suppliers |
| Impact Energy (KV2) | Min. 40 | J | Longitudinal specimen at -20 °C (subject to purchase agreement for high-strength cold-drawn tubes) |
| Hardness | Typically 250-300 | HBW | Reference value for as-drawn condition; not a mandatory standard requirement |
GB/T 3094 Q660 High Strength Cold Completely Equivalent Material Standards and Replaceable Grade Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 3094 | Q660 | Source standard. Specifies cold-drawn square/rectangular tubes. Chemical and mechanical properties are by reference to GB/T 1591 or agreement. |
| Europe | EN 10305-6 | — | This standard covers welded cold-drawn high-strength tubes, but a direct Q660 equivalent must be agreed upon (e.g., a grade with min. 660 MPa yield). S700MC in EN 10305-5 is a comparable base material grade. |
| International | ISO 6930-2 | FeE700 (approximate) | High yield strength steels for cold forming. Minimum yield strength of 700 MPa is close, subject to agreement on tube dimensional tolerances from ISO 10799. |
GB/T 3094 Q660 High Strength Cold Application Introduction
Q660 SHS/RSH pipes are engineered for weight-critical, high-load applications. The exceptional yield strength of 660 MPa allows for significant down-gauging compared to conventional S355 structural tubes, provided that buckling, stiffness, and fatigue resistance are validated through full engineering analysis. Welding requires qualified procedures, typically involving low-hydrogen processes, appropriate preheat, and strict heat input control to avoid cold cracking and preserve the strength of the heat-affected zone.
Product Applications: Prefabricated structural space frames and trusses., Heavy-duty telescopic crane booms and outriggers., Portable bridging systems for emergency and military use., Roll-over protective structures (ROPS) for off-highway vehicles., High-capacity modular scaffolding systems.
Processed into products: Load-bearing columns and beams in seismic-resistant frames., Chassis longitudinal members and crossmembers for heavy transport., Lifting and material handling equipment masts., Support frames for high-pressure piping and industrial equipment., Custom structural nodes and connectors in architectural steelwork.
Application industries: Construction and Infrastructure: High-rise building columns, long-span roof structures, and pedestrian bridges., Heavy Equipment and Machinery: Frames for agricultural harvesters, bulldozers, and excavator arms., Transportation: Truck chassis rails, trailer components, and rail car bodies., Energy Sector: Jack-up rig legs and high-strength structural elements in wind turbine towers., Shipbuilding: Lightweight stiffeners and deckhouse structures for specialized vessels.
GB/T 3094 Q660 High Strength Cold Similar / Approximate Alternative Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10305-5 / EN 10149-2 | S700MC | A thermomechanically rolled high-strength steel for cold forming. Minimum yield strength is 700 MPa, tensile strength 750-950 MPa. Suitable for tubular applications but requires a specific tube standard agreement. |
| USA | ASTM A514 | Grade S (Plate/Strip) | A quenched and tempered high-strength plate steel (min. yield 690 MPa for t≤63.5mm). As a plate source for welded tubes, it provides the necessary strength. Requires a separate hollow section standard (like ASTM A500 for cold-formed welded tubes) to be defined. |
| Japan | JIS G 3128 | SHY 685 / SHY 685N | High yield strength steel plates for welded structures. Minimum yield strength of 685 MPa. Similar strength class for heavy structures; suitable for fabricating tubular sections. |
| China | GB/T 1591 | Q690D/E | High-strength structural steel plate with min. yield of 690 MPa. Can be used to manufacture welded tubes, offering better guaranteed toughness properties (e.g., -20°C, -40°C) than a standard Q660 tube specification, pending purchaser agreement. |
Notes:
- Welding Caution: The carbon equivalent value (CEV) for Q660 is typically 0.50-0.60%, indicating a significant sensitivity to cold cracking. Minimum preheat temperatures (usually 100-200°C based on thickness), low-hydrogen consumables, and controlled interpass temperatures are mandatory. Post-weld heat treatment may be required for highly restrained joints.
- Corner Properties: Cold-drawing of SHS/RSH pipes significantly increases the strength and reduces ductility at corner regions compared to flat faces. This must be considered in structural design, particularly for welded connections at the tube corners.
- Dimensional Tolerances: Governed by GB/T 3094. This includes tight tolerances on outer dimensions, wall thickness (typically +/-10%), straightness, and corner profiles (external corner radius ≤ 3t for main profiles).
- Testing and Certification: Standard inspection certificates (EN 10204 Type 3.1 or equivalent) are provided, specifying heat analysis, mechanical test results for the lot, and confirmation of dimensional checks. Additional tests like non-destructive testing (ultrasonic or eddy current) for the weld seam in welded and drawn tubes are subject to buyer-supplier agreement.
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