JIS G3125 SPA-H Corten Plate

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SPA-H is a kind of weathering-resistant steel, which adopts Japanese steel grade SPA-H. Its chemical composition, mechanical properties and deviation requirements for thickness and width are in accordance with the Japanese standard JISG3125-2004 "High Weathering Resistant Rolled Steel".

Weathering steel SPA-H has good atmospheric corrosion resistance, but also has high temperature, abrasion, molding, fatigue, toughness, plastic extension and other characteristics; can be exposed to use, thinning use or simplify the use of painting. SPA-H rust resistance, can make the component thinning and reduction, resistance to atmospheric corrosion, life extension, with labor-saving and energy-saving properties, so that the component manufacturers, users benefit.

 

Grade	C ≤	Si	Mn	P	S ≤	Cu	Cr	Ni ≤
SPA-H	0.12	0.25~0.75	0.20~0.50	0.070~0.150	0.04	0.25~0.60	0.30~1.25	0.65

 

 

Grade	Plate Thickness	Yield strength	Tensile strength	elongation
SPA-H	6.0mm max	min 345 MPa	min 480 MPa	min22
	6.0mm min	min 335 MPa	min 490 MPa	min 15

 

 

SPA-H (JIS G 3125), Q355GNH (GB/T 4171), and S355J0WP (EN 10025-5) are highly equivalent medium-high strength weathering steels. They share identical anti-corrosion mechanisms (alloyed with Cu, Cr, and P) and highly overlapping yield strengths (~355 MPa). While they can be used interchangeably in most global engineering projects, their core difference lies in low-temperature impact toughness. Q355GNH is the best choice for freezing climates (-20°C), while SPA-H and S355J0WP are ideal for temperate and subtropical regions.

Standard Cross-Reference: Equivalent Grades for SPA-H, Q355GNH, and S355J0WP Weathering Steels

[TL;DR / Quick Summary]
SPA-H (JIS G 3125), Q355GNH (GB/T 4171), and S355J0WP (EN 10025-5) are highly equivalent medium-high strength weathering steels. They share identical anti-corrosion mechanisms (alloyed with Cu, Cr, and P) and highly overlapping yield strengths (~355 MPa). While they can be used interchangeably in most global engineering projects, their core difference lies in low-temperature impact toughness. Q355GNH is the best choice for freezing climates (-20°C), while SPA-H and S355J0WP are ideal for temperate and subtropical regions.

 

1. Origin of Grades and Equivalent Relationship

When sourcing atmospheric corrosion-resistant steel globally, engineers often need to cross-reference standards to optimize costs and lead times. The equivalence of these three grades is based on their highly consistent chemical compositions and mechanical properties:

SPA-H (Japan - JIS G 3125): The undisputed standard for shipping containers and vehicle chassis in Asia.

S355J0WP (Europe - EN 10025-5): The mainstream "W" (weathering) structural steel for EU projects, widely known as the Corten A equivalent.

Q355GNH (China - GB/T 4171): China's upgraded national standard weathering steel, perfectly mirroring the yield strength of S355J0WP while offering superior cold-weather performance.

 

2. Comparison of Core Chemical Compositions

The corrosion resistance of these three grades stems from the "plain carbon steel + corrosion-resistant alloying elements" system. By adding Copper (Cu), Chromium (Cr), and Phosphorus (P), all three grades quickly form a dense, stable oxide rust layer in natural environments.

Below is the exact chemical composition comparison (Mass fraction, %):

lement	SPA-H (JIS G 3125)	Q355GNH (GB/T 4171-2008)	S355J0WP (EN 10025-5)	Explanation of Element Function
C	≤0.18	≤0.18	≤0.17	Ensures steel strength; excessive content reduces toughness and corrosion resistance
Si	0.15~0.55	0.15~0.55	≤0.70	Strengthens ferrite, improves steel strength and oxidation resistance
Mn	0.60~1.20	0.60~1.50	1.00~1.60	Improves steel toughness and weldability, enhances strength
P	0.070~0.150	0.070~0.150	0.070~0.150	A key corrosion-resistant element that promotes the densification of the rust layer and improves atmospheric corrosion resistance
S	≤0.030	≤0.030	≤0.030	A harmful element that reduces toughness and corrosion resistance, requiring strict control of its content
Cu	0.20~0.50	0.20~0.50	0.25~0.55	A core corrosion-resistant element that works synergistically with P and Cr to accelerate the formation of a dense rust layer
Cr	0.30~1.25	0.30~1.25	0.30~1.20	Improves the stability of the rust layer and enhances the corrosion resistance of steel in humid and saline environments
Ni	≤0.65	≤0.65	≤0.65	An auxiliary corrosion-resistant element that improves steel toughness and enhances low-temperature impact performance

 

3. Mechanical Properties & The "Cold Weather" Difference

While their yield and tensile strengths are highly overlapping (positioning all three as medium-high strength structural steels), the most critical difference lies in their Impact Energy (Akv) test temperatures.

Performance Index	SPA-H (JIS G 3125)	Q355GNH (GB/T 4171-2008)	S355J0WP (EN 10025-5)
Yield Strength (Rel)/MPa	≥345	≥355	≥355
Tensile Strength (Rm)/MPa	480~620	470~630	470~630
Elongation (A)/%	≥22	≥21	≥22
Impact Energy (Akv)/J (Test Temperature)	≥27 (-10℃)	≥34 (-20℃)	≥27 (0℃)

 

The Core Takeaway for Engineers:

Q355GNH possesses the highest impact energy (≥34 J) at the lowest temperature (-20℃). It is the absolute best choice for projects in severely cold regions.

SPA-H (-10℃) and S355J0WP (0℃) have slightly lower cold-temperature toughness, making them perfectly suited for temperate and subtropical climates.

 

4. Welding and Usage Guidelines

Because these grades are high-phosphorus weathering steels, they share highly consistent processing and welding methodologies:

• Welding Methods: Support conventional welding and bolted connections. It is highly recommended to use low-hydrogen electrodes (e.g., E5015-G) or weathering-specific welding wire.
• Pre-weld Prep: Rust and oil stains on the groove must be removed completely before welding to prevent defects.
• Heat Control: During rolling or bending, excessive heating should be avoided to prevent the burning loss of valuable alloying elements (Cu, Cr), which would degrade the steel's corrosion resistance.

 

5. Best Practices for Equivalent Substitution

When substituting S355J0WP with SPA-H or Q355GNH to optimize project costs and lead times, follow these 3 critical precautions:

• Consider the Ambient Temperature: If the project is located in a freezing climate (minimum temperature ≤ -20℃), Q355GNH must be prioritized. S355J0WP (tested only at 0℃) should be avoided to prevent brittle fracture.
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• Ensure Design Unit Approval: Always submit a detailed MTC (Mill Test Certificate) showing the chemical composition and mechanical property comparison to your chief engineer for approval prior to substitution.
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• Maintain Welding Consistency: Do not downgrade your welding procedures. The welding parameters and Corten-specific consumables must remain consistent regardless of which equivalent grade you select.

 

Need Help Choosing the Right Weathering Steel?

Selecting between SPA-H, Q355GNH, and S355J0WP involves more than just matching yield strengths-it requires a deep understanding of ambient temperatures and your project's specific corrosion environment.

 

At GNEE STEEL, our technical team can provide detailed chemical analysis reports and mechanical performance verification to ensure your material substitution is 100% safe, compliant, and cost-effective. Contact us today for a quick quote and technical consultation!

 

 

 

 

 

 

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