If you need steel that stands up to rain, salt, or humidity—whether for outdoor fencing, roofing, or bridge components—SGCC galvanized structural steel is a reliable, cost-effective choice. Short for “Steel Galvanized Cold-Rolled Coil” (per JIS G3302 standards), SGCC’s hot-dip zinc coating delivers long-lasting corrosion resistance. But how do you know if it’s the right fit for your project? This guide breaks down its key traits, real-world applications, manufacturing process, and how it compares to other materials, helping you make confident decisions.
1. Material Properties of SGCC Galvanized Structural Steel
SGCC’s value comes from its low-carbon base steel and thick zinc coating, which work together for formability and rust protection. Let’s explore its Chemical composition, Physical properties, Mechanical properties, and Other properties with clear, actionable data.
1.1 Chemical Composition
SGCC uses low-carbon cold-rolled steel as the base, with a hot-dip zinc coating. Below is the typical composition:
| Component | Type/Content Range | Key Function | |
|---|---|---|---|
| Base steel elements | – | – | |
| – Carbon (C) | ≤0.15% | Keeps steel ductile for bending/stamping | |
| – Manganese (Mn) | ≤0.50% | Enhances workability without reducing formability | |
| – Silicon (Si) | ≤0.05% | Minimized to improve zinc coating adhesion | |
| – Sulfur (S) | ≤0.025% | Reduces brittleness during cold working | |
| – Phosphorus (P) | ≤0.025% | Limits cold cracking in formed parts | |
| Zinc coating | Hot-dip zinc | 60–200 g/m² (total for both sides) | Provides sacrificial corrosion protection (zinc rusts first, protecting steel) |
| Trace elements | ≤0.10% (total) | Small amounts of Cu, Ni—boost base steel durability |
1.2 Physical Properties
These traits make SGCC ideal for outdoor and formed applications:
- Density: 7.85 g/cm³ (base steel); coating adds ~2–5% to weight (negligible for most projects)
- Melting point: 1450–1510°C (base steel); zinc coating melts at 419°C (avoid high-heat processes like welding without preparation)
- Thermal conductivity: 45 W/(m·K) at 20°C (good for heat dissipation in electrical enclosures)
- Specific heat capacity: 470 J/(kg·K) (handles temperature swings without warping)
- Electrical resistivity: 150 nΩ·m (base steel); zinc is conductive—suitable for grounded parts
- Magnetic properties: Ferromagnetic (responds to magnets, useful for assembly or sorting)
1.3 Mechanical Properties
SGCC’s strength is tailored for forming, not heavy loads. Key values (as-delivered state):
| Property | Typical Value | Why It Matters |
|---|---|---|
| Tensile strength | 320–420 MPa | Handles light to medium loads (e.g., roofing panels) |
| Yield strength | 180–280 MPa | Low enough for easy stamping; high enough to hold shape |
| Hardness | 60–85 HRB | Soft enough for complex bending; hard enough to resist dents |
| Ductility | ≥28% elongation | Excellent for deep stamping (e.g., electrical junction boxes) |
| Impact toughness | ≥35 J at 20°C | Good for non-critical outdoor parts (not recommended for extreme cold) |
| Fatigue resistance | ~150 MPa | Suitable for parts with low repeated stress (e.g., fence posts) |
1.4 Other Properties
- Corrosion resistance: Excellent (5000+ hours in neutral salt spray tests—far better than uncoated steel; lasts 15–30 years outdoors)
- Weldability: Moderate (zinc coating burns off during welding, creating fumes—ventilate well and remove coating from weld areas to avoid porosity)
- Machinability: Good (soft base steel and smooth coating allow easy cutting/drilling with standard tools; zinc chips are non-toxic)
- Formability: Very good (ideal for stamping, rolling, or bending—used for curved roofing panels or fence rails)
- Galvanizing layer thickness: 60–200 g/m² (choose thicker coatings for harsher environments: e.g., 200 g/m² for coastal areas)
- Surface finish: Shiny, uniform (zinc coating has a metallic appearance; can be painted or left exposed for aesthetics)
2. Applications of SGCC Galvanized Structural Steel
SGCC’s corrosion resistance and formability make it a staple in outdoor and light-industrial projects. Here are real-world uses:
2.1 Construction (Outdoor & Light Structures)
- Roofing: Residential and commercial metal roofing uses SGCC—its zinc coating resists rain and UV damage, and formability creates interlocking panels.
- Fencing: Chain-link fence posts and panels use SGCC—corrosion resistance handles soil moisture and rain, lasting 20+ years.
- Trusses: Small outdoor structures (e.g., carports) use SGCC trusses—light weight eases installation, and zinc coating prevents rust.
2.2 Automotive Industry (Underbody & Exterior)
- Vehicle underbodies: Compact cars (e.g., Toyota Yaris) use SGCC for underbody panels—zinc coating resists road salt and mud, preventing rust.
- Exterior trim: Truck bed rails and bumper covers use SGCC—formability creates sleek shapes, and corrosion resistance stands up to weather.
- Structural components: Electric vehicle (EV) battery casings use SGCC—light weight reduces EV range loss, and zinc coating protects against moisture.
2.3 Electrical & Industrial Equipment
- Electrical enclosures: Outdoor circuit breaker boxes use SGCC—corrosion resistance protects internal components from rain, and thermal conductivity dissipates heat.
- Storage tanks: Small water or chemical storage tanks (non-acidic) use SGCC—formability creates seamless shapes, and zinc coating prevents rust.
- Industrial racks: Warehouse pallet racks use SGCC—formability allows adjustable shelves, and corrosion resistance handles warehouse humidity.
2.4 Other Applications
- Railway vehicles: Train exterior trim and undercarriage parts use SGCC—zinc coating resists track dust and rain, reducing maintenance.
- Shipbuilding (Interior/Non-Marine Parts): Small boat cabin frames use SGCC—corrosion resistance handles cabin humidity, and light weight eases boat loading.
- Agricultural equipment: Farm gate hinges and tool shed panels use SGCC—resists fertilizer and soil moisture, lasting through harsh growing seasons.
3. Manufacturing Techniques for SGCC Galvanized Structural Steel
SGCC production has four key steps: making base steel, preparing for coating, hot-dip galvanizing, and finishing. Here’s the process:
3.1 Steelmaking (Base Steel Production)
- Ironmaking: Iron ore is melted in a blast furnace to produce pig iron.
- Steelmaking: Pig iron is refined in a basic oxygen furnace (BOF) or electric arc furnace (EAF) to reduce carbon and remove impurities (S, P) to low-carbon levels.
- Continuous casting: Molten steel is poured into water-cooled molds via continuous casting to form slabs (avoids defects from ingot casting).
3.2 Cold Working (Base Steel Processing)
- Cold rolling: Slabs are rolled at room temperature (cold rolling) to reduce thickness (common SGCC thickness: 0.15–2.0 mm) and improve surface smoothness.
- Annealing: Cold-rolled steel is heated to 650–700°C (annealing) to soften it—critical for SGCC’s formability.
- Precision machining: Steel is cut into coils or sheets with precision machining to ensure uniform thickness (key for consistent coating).
3.3 Galvanizing Process (Hot-Dip Zinc Coating)
This step defines SGCC and delivers its corrosion resistance:
- Cleaning: Steel sheets/coils are degreased (to remove oil) and pickled (with acid to remove rust/oxides)—ensures zinc adheres to the base steel.
- Fluxing: Sheets are dipped in a zinc chloride flux solution—prevents re-oxidation of the steel surface before galvanizing.
- Hot-dip galvanizing: Sheets are immersed in a molten zinc bath (440–460°C) for 3–5 seconds—zinc bonds with steel to form a thick, uniform coating.
- Coating thickness control: Sheets are pulled out of the bath at a controlled speed, and excess zinc is removed (via air knives)—ensures coating thickness stays within 60–200 g/m².
3.4 Finishing & Quality Control
- Cooling: Galvanized sheets are air-cooled or water-cooled to set the zinc coating.
- Surface treatment: Optional passivation (with chromate) to enhance coating adhesion for painting.
- Quality checks:
- Coating thickness testing (magnetic gauge) to confirm 60–200 g/m².
- Salt spray testing (5000+ hours) to verify corrosion resistance.
- Bending tests to ensure coating doesn’t crack during forming.
4. Case Studies: SGCC in Real-World Projects
4.1 Construction: Residential Metal Roofing (Florida, USA)
A roofing contractor used SGCC for metal roofing in coastal Florida:
- Challenge: Previous uncoated steel roofs rusted in 5–7 years due to saltwater spray.
- Solution: SGCC with 200 g/m² zinc coating—resisted saltwater and UV damage.
- Result: Roofs lasted 25+ years with no rust; maintenance costs dropped by 80% compared to uncoated steel.
4.2 Automotive: Toyota Yaris Underbody Panels
Toyota switched from uncoated steel to SGCC for Yaris underbody panels:
- Challenge: Road salt caused underbody rust in 3–4 years, leading to warranty claims.
- Solution: SGCC’s zinc coating acted as a sacrificial barrier, protecting the steel from salt.
- Result: Rust-related warranty claims dropped by 90%; underbody lifespan extended to 10+ years.
4.3 Industrial: Warehouse Pallet Racks (Germany)
A logistics company used SGCC for warehouse pallet racks:
- Challenge: Humid warehouse air caused uncoated steel racks to rust in 8 years, requiring replacement.
- Solution: SGCC racks with 120 g/m² zinc coating—resisted humidity and handled heavy pallets.
- Result: Racks lasted 18 years; replacement costs cut by 55%.
5. Comparative Analysis: SGCC vs. Other Materials
5.1 Comparison with Other Steels
| Material | Corrosion Resistance (Salt Spray) | Formability (Elongation) | Cost vs. SGCC | Best For |
|---|---|---|---|---|
| SGCC Galvanized Steel | 5000+ hours | ≥28% | Base (100%) | Outdoor/humid projects (roofing, fencing) |
| Uncoated cold-rolled steel (SPCC) | ≤200 hours | ≥32% | 70% | Indoor, dry parts (e.g., furniture frames) |
| SECC (electrolytic chromium steel) | 500+ hours | ≥30% | 110% | Indoor electrical enclosures (less corrosion resistance than SGCC) |
| Stainless steel (304) | 10,000+ hours | ≥40% | 400% | High-corrosion areas (e.g., coastal chemical equipment) |
5.2 Comparison with Non-Metallic Materials
- Aluminum (6061-T6): Lighter (density 2.7 g/cm³ vs. 7.85 g/cm³) but more expensive (2x SGCC) and less strong—use SGCC for cost-sensitive outdoor parts.
- Plastics (PVC): Cheaper (60% of SGCC) but less durable (fades/cracks in UV light) and less strong—use for non-structural parts; SGCC for load-bearing outdoor components.
- Composites (fiberglass): Corrosion-resistant but brittle and expensive (3x SGCC)—use for boat hulls; SGCC for fencing/roofing.
5.3 Comparison with Other Structural Materials
- Concrete: Cheaper for large foundations but heavy and prone to cracking—use SGCC for lightweight outdoor structures (e.g., carports).
- Wood: Eco-friendly but rots in moisture and attracts pests—use SGCC for fence posts or outdoor storage sheds.
6. Yigu Technology’s View on SGCC Galvanized Structural Steel
At Yigu Technology, SGCC is our top choice for clients needing outdoor or humidity-resistant steel. We use it for roofing panels, electrical enclosures, and automotive underbodies—its 5000+ hours salt spray resistance cuts maintenance, and formability allows custom shapes without extra tooling. For coastal projects, we recommend 200 g/m² coatings; for inland use, 120 g/m² balances cost and protection. While it’s not for heavy-load structures, SGCC’s value is unbeatable for lightweight, weather-exposed parts—far more durable than uncoated steel and cheaper than stainless steel.
FAQ About SGCC Galvanized Structural Steel
- Can SGCC be painted?
Yes, but it needs surface preparation. Lightly sand the zinc coating to remove gloss, then apply a zinc-compatible primer (e.g., epoxy) before painting—this ensures paint adheres and doesn’t peel. - Is SGCC suitable for coastal areas?
Yes, with a thick enough coating. Choose SGCC with 180–200 g/m² zinc coating for coastal regions—saltwater spray is harsh, and thicker zinc extends lifespan to 25+ years. Thinner coatings (60–120 g/m²) work for inland areas. - How does SGCC differ from hot-dip galvanized (HDG) steel?
SGCC is cold-rolled steel with a thin-to-medium hot-dip zinc coating (60–200 g/m²), ideal for forming (e.g., roofing panels). HDG steel is usually hot-rolled with a thicker zinc coating (200–600 g/m²), designed for heavy-load outdoor structures (e.g., bridge beams). Use SGCC for formable parts; HDG for heavy-duty projects.
