GB/T 3094 45# SHS/RSH Pipe
GB/T 3094 45# SHS/RSH Pipe | Cold Drawn Carbon Steel Square & Rectangular Hollow Section
Comprehensive data on 45# carbon steel square and rectangular hollow sections per GB/T 3094: chemical composition, mechanical properties, thermal and electrical physical data, equivalent grades, and application guidance.
Cold drawing, cutting, machining, welding (with preheating), heat treatment (quenching & tempering, annealing)
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GB/T 3094 45# SHS/RSH Pipe Introduction
GB/T 3094 45# steel pipe is a cold-drawn seamless square (SHS) and rectangular (RHS) hollow section produced from quality carbon structural steel Grade 45 (45#). It is characterized by medium carbon content (0.42–0.50% C), providing a good balance of strength, toughness, and machinability. The cold-drawing process ensures precise dimensions, smooth surface finish, and enhanced mechanical properties. Typical delivery condition is cold-drawn (hard) or annealed. This material can be further heat treated (quenching and tempering) to increase hardness and wear resistance. It is widely used in mechanical engineering, automotive, hydraulic, and structural applications where higher strength than mild steel is required.
GB/T 3094 45# SHS/RSH Pipe Chemical Composition
Chemical composition of steel grade 45 for GB/T 3094 pipe shall conform to GB/T 699. It is a medium carbon steel with controlled residual elements.
- Carbon provides hardenability and strength.
- Silicon and manganese act as deoxidizers and strengtheners.
- Phosphorus and sulfur are kept low to maintain ductility and toughness.
| Element | Standard Value (%) | Remarks |
|---|---|---|
| Carbon (C) | 0.42 – 0.50 | Primary hardening element |
| Silicon (Si) | 0.17 – 0.37 | Deoxidizer; improves strength |
| Manganese (Mn) | 0.50 – 0.80 | Hardenability and strength |
| Phosphorus (P) | ≤ 0.035 | Impurity – maximum limit |
| Sulfur (S) | ≤ 0.035 | Impurity – maximum limit |
| Chromium (Cr) | ≤ 0.25 | Residual element |
| Nickel (Ni) | ≤ 0.30 | Residual element |
| Copper (Cu) | ≤ 0.25 | Residual element |
GB/T 3094 45# SHS/RSH Pipe Thermal and Electrical Physical Properties
Physical properties for 45# carbon steel (Grade 45) are typical for medium carbon steel. Values are indicative and may vary slightly with heat treatment and temperature.
- Thermal expansion increases with temperature.
- Thermal conductivity decreases as temperature rises.
- Electrical resistivity is given at room temperature.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Elastic modulus (E) | 206 | GPa | At 20 °C |
| Shear modulus (G) | 80 | GPa | At 20 °C |
| Poisson's ratio (ν) | 0.30 | – | At 20 °C |
| Thermal expansion (α) | 11.7 | 10⁻⁶/K | 20–100 °C |
| Thermal expansion (α) | 12.5 | 10⁻⁶/K | 20–200 °C |
| Thermal expansion (α) | 13.2 | 10⁻⁶/K | 20–300 °C |
| Thermal conductivity (λ) | 48 | W/(m·K) | At 20 °C |
| Thermal conductivity (λ) | 46 | W/(m·K) | At 100 °C |
| Specific heat capacity | 486 | J/(kg·K) | At 20 °C |
| Electrical resistivity (ρₑ) | 0.17 | 10⁻⁶ Ω·m | At 20 °C |
GB/T 3094 45# SHS/RSH Pipe Mechanical Properties
The following mechanical properties are minimum required values for cold-drawn condition as specified in GB/T 3094. Testing is performed at room temperature.
- Actual values in finished tubes may exceed these minima.
- If annealing is required by the purchaser, the mechanical properties shall be agreed upon between the manufacturer and purchaser.
- No impact test is mandatory for this standard.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Yield strength (ReH) | ≥ 335 | MPa | Cold drawn, room temperature |
| Tensile strength (Rm) | ≥ 590 | MPa | Cold drawn, room temperature |
| Elongation (A) | ≥ 14 | % | Gauge length 5.65√S₀, cold drawn |
GB/T 3094 45# SHS/RSH Pipe Fully Equivalent Material Standards & Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 8162 | 45# | Structural seamless steel pipe, cold drawn |
| USA | ASTM A519 | 1045 | Cold drawn seamless carbon steel mechanical tubing |
| Europe | EN 10305-1 | C45E | Cold drawn seamless precision steel tube |
| Germany (historical) | DIN 2391-2 | St45 | Seamless precision steel tube, replaced by EN 10305-1 |
GB/T 3094 45# SHS/RSH Pipe Application Introduction
45# carbon steel SHS/RHS pipes are used where moderate strength and excellent machinability are required. The cold-drawn surface and tight tolerances make them suitable for precision mechanical components. Typical application areas include:
Product Applications: Hydraulic cylinders, Piston rods, Rollers and conveyor parts, Axle housings, Machine tool spindles, Transmission shafts, Furniture frames
Processed into products: Cylinder barrels, Bushings, Sleeves and spacers, Couplings, Frame connectors, Column guides, Wear plates (after hardening)
Application industries: Machinery manufacturing, Automotive industry, Hydraulics & pneumatics, Agricultural machinery, Metal furniture, Construction and structural frames
GB/T 3094 45# SHS/RSH Pipe Similar / Alternative Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 3094 | Q345B | Low-alloy high-strength steel, better weldability |
| Europe | EN 10210 | S355J2H | Hot-finished structural hollow section, similar yield strength (355 MPa) |
| USA | ASTM A500 | Grade C | Cold-formed welded structural tubing, yield 345 MPa |
| China | GB/T 8162 | 20# | Lower carbon, higher toughness alternative |
| China | GB/T 3077 | 40Cr | Alloy steel, quenched & tempered for high-strength parts |
Notes:
Welding: 45# steel has medium carbon content (CE ~0.65%) and is susceptible to hardening in the heat-affected zone. Preheating to 150–250 °C and stress-relief annealing after welding are recommended. Heat treatment: Quenching and tempering can significantly increase hardness (up to ~55 HRC) and strength for wear-resistant components. Surface condition: As per GB/T 3094, surfaces are free from scale and rust; pickled or oiled finishes are available. Dimensional tolerances follow the standard's advanced or ordinary classes. Alternative selection: For applications requiring excellent weldability and toughness, consider low-carbon or low-alloy options like Q345B or S355J2H.
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