JIS G3125 SPA-C Weather Resistant Steel
JIS G3125 SPA-C Weather Resistant Steel: Complete Guide to Properties, Equivalents & Uses
Detailed technical data for JIS G3125 SPA-C weather-resistant steel coil including chemical composition, mechanical and physical properties, international equivalents, similar materials, and application guidance. Trusted data from JIS standards.
Cutting, blanking, bending, roll forming, stamping, welding (with proper procedures), punching, shearing
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JIS G3125 SPA-C Weather Resistant Steel Introduction
JIS G3125 SPA-C is a high-strength, low-alloy weather-resistant steel (also known as atmospheric corrosion-resistant steel) developed in Japan. It is primarily supplied as cold-rolled steel coil, strip, and sheet. By adding alloying elements such as copper, chromium, and phosphorus, a dense and protective patina forms on the surface when exposed to the atmosphere, significantly slowing down further corrosion. This eliminates the need for painting or other protective coatings in many outdoor applications.
Key features include:
- Excellent atmospheric corrosion resistance – 2 to 8 times that of ordinary carbon steel.
- Minimum yield strength of 315 MPa, providing good structural strength.
- Good cold formability and weldability, enabling efficient fabrication.
- Cost-effective through reduced maintenance and longer service life.
SPA-C is widely used in containers, railway vehicles, building exteriors, and various structural components exposed to weather.
JIS G3125 SPA-C Weather Resistant Steel Chemical Composition
The chemical composition of JIS G3125 SPA-C is specifically designed to promote the formation of a stable, adherent rust layer that protects the base metal. Phosphorus contributes significantly to corrosion resistance, while copper and chromium enhance the patina's protective qualities. The composition limits are per the JIS G3125:2004 standard.
- All values are mass percentages from heat analysis.
- Elements not listed are not intentionally added and are restricted by the total other elements requirement.
| Element | Standard Value (%) | Remarks |
|---|---|---|
| C (Carbon) | ≤ 0.12 | Improves strength; kept low for weldability |
| Si (Silicon) | 0.25 – 0.75 | Deoxidizer; contributes to strength and weather resistance |
| Mn (Manganese) | 0.20 – 0.50 | Enhances strength and hardenability; controlled to prevent hot shortness |
| P (Phosphorus) | 0.070 – 0.150 | Key element for atmospheric corrosion resistance |
| S (Sulfur) | ≤ 0.040 | Controlled to maintain toughness and formability |
| Cu (Copper) | 0.25 – 0.60 | Primary alloy for improved weather resistance by patina formation |
| Cr (Chromium) | 0.30 – 1.25 | Enhances corrosion resistance and mechanical properties |
| Ni (Nickel) | ≤ 0.65 | Improves toughness and adds corrosion resistance in marine environments |
| Others | Balance Fe | Typical residual elements (Al, N, etc.) are kept to standard levels |
JIS G3125 SPA-C Weather Resistant Steel Thermal and Electrical Physical Properties
Physical properties for JIS G3125 SPA-C are not specified in the standard but are typical for a phosphorus-alloyed low-alloy weathering steel at ambient temperature. Actual values can vary slightly with composition and processing.
- Data provided for engineering calculations and design.
- For elevated temperatures, thermal expansion and conductivity change; refer to specific material data sheets.
| Property | Typical Value | Unit | Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Modulus of Elasticity (E) | 205 | GPa | Tensile modulus, room temperature |
| Shear Modulus (G) | 80 | GPa | Approximately 0.385 × E |
| Poisson's Ratio (ν) | 0.29 | - | Elastic range |
| Thermal Expansion Coefficient (α) | 12.0 | 10⁻⁶/K | 20 – 100 °C range |
| Thermal Conductivity (λ) | 42 | W/(m·K) | At 20 °C |
| Specific Heat Capacity (c) | 480 | J/(kg·K) | At 20–100 °C |
| Electrical Resistivity (ρ_e) | 0.25 | µΩ·m | At room temperature |
JIS G3125 SPA-C Weather Resistant Steel Mechanical Properties
Mechanical properties for JIS G3125 SPA-C cold-rolled sheet and strip are guaranteed at room temperature. Tests are performed according to JIS Z 2241 (tensile) and JIS Z 2248 (bend). The specified values are minimum unless a range is given.
- Yield strength and elongation depend on thickness and specimen type.
- Values below are for the most commonly supplied thickness range (≤ 6 mm).
| Property | Requirements | Unit | Test Condition / Remarks |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 315 | MPa (N/mm²) | Thickness ≤ 6 mm |
| Tensile Strength (Rm) | ≥ 450 | MPa (N/mm²) | Thickness ≤ 6 mm |
| Elongation (A) | ≥ 26 | % | JIS No.5 specimen, gauge length 50 mm, thickness ≤ 6 mm |
| Elongation (A) | ≥ 20 | % | JIS No.1A specimen, thickness 6 mm < t ≤ 16 mm |
| Elongation (A) | ≥ 18 | % | JIS No.1A specimen, thickness > 16 mm |
| Bend Test (180°) | Inside radius 1.0t | - | No cracks, thickness ≤ 6 mm, t = specimen thickness |
| Bend Test (180°) | Inside radius 1.5t | - | No cracks, thickness 6 mm < t ≤ 16 mm |
JIS G3125 SPA-C Weather Resistant Steel Exact International Equivalents and Replaceable Grades
| Country / Region | Standard | Grade / Designation | Remarks |
|---|---|---|---|
| USA | ASTM A606 / A606M | Type 4 or Type 2 | Hot/cold-rolled HSLA weathering steel; Type 4 has higher Cr content. SPA-C is most similar to Type 4. |
| Europe | EN 10025-5 | S355J2W | Similar strength and corrosion resistance; slight differences in chemical composition limits. |
| China | GB/T 4171 | Q355NH | Chinese weathering steel with comparable mechanical properties; check dimensional tolerances. |
| International | ISO 4952 | S355W | ISO weathering structural steel, closely matches mechanical and corrosion requirements. |
| Japan | JIS G3125 | SPA-H | Hot-rolled variant of the same standard; substitute when thickness or surface condition allows. |
JIS G3125 SPA-C Weather Resistant Steel Application Introduction
JIS G3125 SPA-C is engineered for structural and aesthetic applications where long-term exposure to the atmosphere is expected without maintenance coating. Its typical thickness range (0.6–2.3 mm as cold-rolled) makes it ideal for sheet metal fabrications. When designing, consider the following:
- Welding: Use low-hydrogen electrodes or filler metals intended for weathering steel; preheat may be necessary for thicker sections.
- Painting: Not required for corrosion resistance, but if a specific aesthetic is desired, the patina can be painted after tightly adhering rust layer formation.
- Forming: Excellent cold formability, similar to low-carbon steel of comparable strength.
Recommended industries, products, and typical components are listed below.
Product Applications: ISO shipping containers (dry and refrigerated), Railway passenger coach bodies, freight wagon side frames and roofs, Prefabricated modular buildings and guard houses, Architectural wall panels and curtain wall systems, Metal silos and bins for outdoor storage, Bicycle racks and street furniture
Processed into products: Container corrugated side sheets, roof panels, and end frames, Roll-formed structural C-channels and Z-purlins for building trusses, Bent and spot-welded brackets and supports for cladding systems, Laser-cut decorative facade elements, Stamped railway car interior panels and window frames, Welded ductwork and expansion joints for flue gas systems, Bolted connection plates in lightweight framed structures
Application industries: Shipping and container logistics, Railway car manufacturing (passenger and freight), Architecture and construction (cladding, roofing, facades), Bridge engineering (pedestrian bridges, highway sound barriers), Power and energy (chimney flues, air pollution control equipment), Agricultural equipment and grain bins, Outdoor sculptures and art installations
JIS G3125 SPA-C Weather Resistant Steel Similar / Closely Related Material Recommendations
| Country / Region | Standard | Grade | Remarks / Analysis |
|---|---|---|---|
| Japan | JIS G3125 | SPA-H | Hot-rolled version of SPA-C with identical chemical composition but thicker gauge availability; may have slightly lower yield strength for thicker sections. |
| USA | ASTM A588 | Grade A / Grade B / Grade C | High-strength low-alloy structural weathering steel; used in thicker sections, weldability similar, but phosphorus level is lower. |
| USA | ASTM A242 | Type 1 | Older weathering steel standard; similar corrosion resistance but can have slightly different alloy design. |
| Europe | EN 10025-5 | S355J0W / S355J2W | European weathering steel; lower phosphorus content, thus slightly different patina behavior and superior toughness in cold conditions. |
| India | IS 11587 | Fe540W | Indian weathering steel with comparable strength, check for exact equivalence before substitution. |
| Korea | KS D 3529 | SPA-C | Korean Industrial Standard directly adopts JIS designation; identical requirements. |
Notes:
- Data is based on JIS G3125:2004 official standard. For precise acceptance criteria, always refer to the original standard or the material certificate from the mill.
- When used in aggressive marine or industrial atmospheres (high chloride or sulfur dioxide), design details should ensure proper drainage and avoid crevices to maximize the benefits of the weathering steel.
- SPA-C is not a direct equivalent to the proprietary Corten A (which generally has higher phosphorus), but it provides comparable performance in most environments.
- For painting, thorough surface preparation (blast cleaning SSPC-SP6 or SP10) is recommended to remove loose oxide scale if applied before natural patina formation.
- The cold-rolled surface may be supplied with a rust-preventative oil; this must be removed before welding or painting.
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