S350GD is a high-strength structural galvanized steel, which is specially designed for load-bearing applications, while DX51D is a commercial-grade mild steel with excellent formability, which is an ideal choice for general bending and forming operations. As a leading supplier of galvanized steel in China, Runfei Group provides tailor-made coated steel solutions for global construction and industrial projects to maximize corrosion resistance and performance. The choice between these two grades depends entirely on the structural requirements, molding complexity and environmental conditions of the project.
What is DX51D Galvanized Steel Plate?
DX51D galvanized steel conforms to the EN 10346 European standard, representing the most widely used commercial-quality continuous hot-dip galvanized steel grade. Its substrate is usually low-carbon steel or cold-rolled steel, which is treated with a pure zinc (Z) coating to provide reliable atmospheric protection. The classification of names clarifies its characteristics: “D” stands for cold forming ability, “X” stands for unspecified rolling state (hot rolling or cold rolling), and “51” stands for standard commercial quality serial number.
This kind of steel shows excellent ductility and formability, with a minimum elongation of 22% and yield strength of 140-300 MPa. Its excellent bending performance allows 180-degree bending without cracking of the coating, even at a small radius. For applications requiring higher formability, enhanced ductility grades DX52D Z and DX53D Z can be provided, providing minimum elongation of 26% and 30%, respectively.
DX51D Z (commonly called GI steel) is the first choice for pre-painted galvanized steel products such as PPGI and PPGL. The main applications include roof slabs, wall cladding, ventilation pipes, garage doors and various molding components whose structural strength is second only to molding ability. Its cost efficiency and reliable corrosion resistance make it the industry standard for non-load-bearing building components.
What is S350GD Structural Galvanized Steel?
S350GD is a high-strength structural galvanized steel grade defined by EN 10346, where “S” stands for structure, “350” stands for minimum yield strength of 350 MPa, and “GD” stands for dual-phase characteristics of zinc plating. Designed for structural applications, this grade can provide excellent load-bearing capacity while maintaining sufficient formability for basic manufacturing.
The typical yield strength of S350GD is 360-400 MPa, and tensile strength is 420-540 MPa, which is superior to traditional carbon steel substitutes. Different from purchasing Q235, Q355, S355JR or ST 37 steel and then hot-dip galvanizing, the pre-coating S350GD eliminates the coating processes after manufacturing, which significantly improves production efficiency and quality consistency.
This kind of structural grade is dominant in applications requiring a high strength-to-weight ratio and wind, snow and earthquake loads. The main applications include photovoltaic bracket systems, solar bracket structures, purlins, supporting frames, light steel frames and special installation system components in renewable energy and heavy buildings. Its combination of strength and corrosion resistance makes it indispensable for modern infrastructure projects.
S350GD vs. DX51D: Side-by-Side Comparison
| Property | DX51D Galvanized Steel | S350GD Structural Galvanized Steel |
| Base Material | Commercial Quality (mild/cold rolled steel) | High-Strength Structural Grade |
| Yield Strength | 140-300 MPa (no strict minimum) | ≥350 MPa (minimum guaranteed) |
| Tensile Strength | 270-500 MPa | 420-540 MPa |
| Elongation | ≥22% (excellent ductility) | 17-22% (good for structural bending) |
| Formability | Excellent (complex deep drawing/bending) | Fair (simple bends only; significant springback) |
| Primary Use | Non-structural forming applications | Load-bearing structural components |
| Cost Efficiency | Lower material cost; ideal for simple parts | Higher cost justified by structural performance |
| Typical Coatings | Z (pure zinc), ZA, ZF | Z, ZA, AZ (GALVALUME/ALUZINC STEEL) |
How to choose the appropriate level for your Project?
For Roofing and Cladding
DX51D is undoubtedly the best choice for the application of standard roofing board and wall coating. Its excellent formability enables it to be accurately molded into complex profiles, and the zinc coating provides excellent corrosion resistance for the external wall of a building. When completed as PPGI and PPGL, DX51D provides excellent aesthetic qualities and long-term durability. The flexibility of this material reduces the manufacturing costs and allows for effective installation, making it the industry standard for building applications.
Used for Solar Structures and Heavy-Duty Supports
The structural grade of S350GD or higher is mandatory for solar support systems and heavy-duty support applications. These structures must be able to withstand extreme wind lift, snow loads and environmental stresses with a life span of more than 25 years. In highly corrosive environments, such as coastal areas or industrial areas, ZAM steel (zinc-aluminum-magnesium) or alumina steel /galvalume coating is specified to maximize the performance of corrosion-resistant steel. The corrosion resistance of these advanced coatings is 2-3 times that of standard galvanized coatings, especially at the cutting edges and welding points.
Why source from Runfei Group?
As a premier galvanized steel Manufacturer, Runfei Group combines decades of expertise with state-of-the-art production facilities. Our galvanized steel mill located in Hangu Industrial Park in Tianjin covers an area of 170 acres, with an annual processing capacity of 300,000 tons, ensuring a reliable supply for projects of any size.
In addition to the basic galvanized steel coils, we also provide a comprehensive one-stop solution. As a reliable roofing board manufacturer and installation system factory, we provide customized cutting, bending and manufacturing services to meet accurate project specifications. Our strict quality control agreement ensures that accurate steel tolerances meet EN, ASTM and JIS standards, and are supported by complete factory test certificates.
With export operations since 2004, we’ve established a global logistics network ensuring timely delivery to over 80 countries. Our technical team provides customers with suggestions on material selection, design optimization and cost saving, making Runfei Group the first choice for international construction and renewable energy projects.
Frequently Asked Questions
Q: Can I use DX51D to make a solar installation system?
A: No. DX51D lacks the necessary yield strength to support the structural loads required for mounting system product applications. Its soft, ductile nature cannot withstand wind, snow, and seismic forces, creating significant safety risks and potential structural failure. For solar supporting structures, always specify the structural level of S350GD or higher.
Q: What is the difference between GI and GL?
A: GI (galvanized iron) refers to pure galvanized steel, while GL refers to GALVALUME/ alumina steel with a 55% aluminum-zinc alloy coating. The corrosion resistance of GL coatings is 2-4 times higher than that of standard GI coating, especially in coastal and industrial environments. As a professional galvanized steel company, Runfei provides two kinds of coatings with different thicknesses to meet specific project requirements.
Q: Which level provides better cost-effectiveness for my project?
Answer: Cost-effectiveness depends entirely on the application. DX51D provides a higher value for non-structural and highly formed parts that have nothing to do with strength. S350GD provides better long-term value for structural applications by reducing material thickness requirements while maintaining a safety margin, usually through material optimization, and the overall cost is saved.
Q: Can S350GD be formed into complex shapes like DX51D?
A: Limited. While S350GD allows simple bends, its high strength causes significant springback and limits forming complexity. For deep drawing or complex shapes, DX51D, DX52D Z, or DX53D Z are still the only practical choices, although their strength is low.
Conclusion
In a word, DX51D is the best choice when giving priority to the formability and cost-effectiveness of non-structural components such as roofing sheets and cladding. However, for load-bearing applications, such as solar support systems and structural support, the minimum yield strength of 350 MPa is required, and S350GD is the indispensable and performance-proven solution. Your choice directly affects structural integrity, long-term durability and project economy.
As a leading exporter of galvanized steel, Runfei Group provides not only standard materials but also customized galvanized steel solutions tailored to your specific specifications. In addition to galvanized steel, our comprehensive product range includes high-quality carbon steel product series and precision steel pipes, providing complete material solutions from a reliable source.
Material selection involves key factors other than grade designation, including coating thickness, steel tolerance, width/length specifications and surface treatment requirements. Our technical team is ready to analyze your project drawings and provide optimized material suggestions at a competitive price. Please contact Runfei Group immediately to ensure that your next project uses the perfect coated steel solution to realize the highest performance and value.
