Weathering steel, also referred to as atmospheric corrosion-resistant steel, achieves enhanced corrosion resistance through the intentional addition of specific alloying elements to conventional carbon steel.
These alloying elements promote the formation of a dense, adherent, and stable oxide (rust) layer under natural atmospheric conditions. This protective patina effectively shields the steel substrate from further corrosion caused by atmospheric moisture, industrial pollutants, and marine environments, thereby significantly extending service life and reducing maintenance costs.
SPA-H, Q355GNH, and S355J0WP are three widely applied weathering steel grades in industrial and structural engineering. Among them, Q355GNH and S355J0WP have a clear one-to-one equivalence, while SPA-H, although governed by a different standard system, demonstrates strong compatibility with the other two in terms of chemical design, mechanical performance, and application scenarios.
This article provides a systematic comparison of the three grades from the perspectives of standard origin, chemical composition, mechanical properties, application scenarios, and substitution considerations, offering practical guidance for engineering material selection.
Origin of Grades and Definition of Equivalent Relationships
The three grades originate from different national or regional standards. Their equivalence is established primarily through similarities in chemical composition, mechanical properties, and intended applications:
SPA-H
Defined in JIS G 3125 (Japan), SPA-H is a weathering structural steel designed for long-term atmospheric exposure. It is widely used in buildings, bridges, vehicles, containers, and other structural components requiring corrosion resistance.
Q355GNH
Specified in GB/T 4171-2008 (China), Q355GNH is a low-alloy high-strength weathering steel upgraded from Q345GNH. With a nominal yield strength of 355 MPa, it represents the mainstream weathering steel grade in China.
S355J0WP
Defined under EN 10025-5 (Europe), S355J0WP belongs to the "W" (weathering) steel family. The designation "J0" indicates an impact toughness requirement of ≥27 J at 0°C. Its yield strength level matches that of Q355GNH, making the two grades direct equivalents for structural applications.
In practice, Q355GNH and S355J0WP are fully interchangeable equivalents between Chinese and European standards. Although SPA-H does not have an official one-to-one equivalent designation in GB or EN systems, it is frequently accepted as an alternative due to its closely matched chemical composition, mechanical performance, and overlapping application fields.
Comparison of Core Chemical Compositions
The corrosion resistance of weathering steel primarily originates from alloying elements such as Cu, Cr, and P, which facilitate the formation of a compact and protective rust layer. All three grades follow the same design philosophy: carbon steel base + corrosion-resistant alloying elements.
Chemical Composition Comparison (% by mass)
| Element | SPA-H (JIS G 3125) | Q355GNH (GB/T 4171) | S355J0WP (EN 10025-5) | Function |
|---|---|---|---|---|
| C | ≤0.18 | ≤0.18 | ≤0.17 | Strength control; excessive C reduces toughness and corrosion resistance |
| Si | 0.15–0.55 | 0.15–0.55 | ≤0.70 | Strengthens ferrite, improves oxidation resistance |
| Mn | 0.60–1.20 | 0.60–1.50 | 1.00–1.60 | Enhances strength, toughness, and weldability |
| P | 0.070–0.150 | 0.070–0.150 | 0.070–0.150 | Key element for rust layer densification |
| S | ≤0.030 | ≤0.030 | ≤0.030 | Harmful impurity, strictly limited |
| Cu | 0.20–0.50 | 0.20–0.50 | 0.25–0.55 | Core corrosion-resistant element |
| Cr | 0.30–1.25 | 0.30–1.25 | 0.30–1.20 | Improves rust layer stability |
| Ni | ≤0.65 | ≤0.65 | ≤0.65 | Enhances toughness and low-temperature performance |
Comparison of Core Mechanical Properties
All three grades are classified as medium-to-high strength weathering structural steels, with nominal yield strength levels around 355 MPa.
Mechanical Property Comparison (Hot-Rolled, t ≤ 16 mm)
| Property | SPA-H | Q355GNH | S355J0WP |
|---|---|---|---|
| Yield Strength (MPa) | ≥345 | ≥355 | ≥355 |
| Tensile Strength (MPa) | 480–620 | 470–630 | 470–630 |
| Elongation (%) | ≥22 | ≥21 | ≥22 |
| Impact Energy | ≥27 J @ −10°C | ≥34 J @ −20°C | ≥27 J @ 0°C |
Yield and tensile strength ranges largely overlap. Although SPA-H has a slightly lower specified yield limit, practical production often meets or exceeds 355 MPa.
All three grades meet structural plasticity requirements. Q355GNH demonstrates superior low-temperature toughness, making it particularly suitable for cold regions. SPA-H and S355J0WP are better suited to temperate climates.
Usage Methods and Application Scenarios
(1) Common Usage Characteristics
Processing:
All grades support hot and cold forming, including rolling, bending, stamping, and cutting. Excessive heating should be avoided to prevent alloy burn-off.
Welding:
Standard welding methods are applicable. Low-hydrogen electrodes (e.g., E5015-G) are recommended. Pre-weld cleaning and post-weld slag removal are essential.
Surface Protection:
Weathering steels can be used uncoated in open atmospheric environments. For marine or enclosed high-humidity environments, additional surface treatments such as phosphating and fluorocarbon coating are recommended.
(2) Application Emphasis by Grade
SPA-H:
Common in Japan, Southeast Asia, containers, port equipment, and Japanese automotive structures. Suitable for temperate and subtropical regions.
Q355GNH:
Widely used in China for bridges, buildings, construction machinery, and infrastructure, including cold regions due to excellent low-temperature toughness.
S355J0WP:
Preferred for EU projects and international engineering. Best suited for temperate climates; cold-region use requires additional toughness verification.
What is spa H material?
As Spa-h steel coil material is a weathering steel, it forms the protective patina on the surface which gives it a rustic appearance. The chemical composition of the JIS g3125 spa-h strip includes carbon, silicon, manganese, phosphorus, sulphur, copper, chromium and nickel.
What is spa-h steel equivalent?
Worldwide equivalents of grade SPA-H (Japan: JIS ) Cross reference table for Steel SPA-H (JIS ) and its European equivalent S355J0WP (1.8945)
What is the chemical composition of SPA-H Steel?
The main elements include carbon (C), manganese (Mn), silicon (Si), chromium (Cr), and copper (Cu). Their contents are strictly controlled to ensure mechanical properties and weather resistance.
How to maintain SPA-H Steel?
SPA-H steel requires minimal maintenance. A stable rust layer protects the steel. Regular cleaning to remove dust or debris and avoiding prolonged water exposure is sufficient.
Can SPA-H Steel be welded?
Yes. Low-hydrogen arc welding or gas shielded welding is recommended. Preheating and slow cooling after welding help prevent cracking.
| CORTEN | Corten A | Corten B | ||
| ASTM A588/A588M | A588 Grade A | A588 Grade B | A588 Grade C | A588 Grade K |
| ASME SA588/SA588M | SA588 Grade A | SA588 Grade B | SA588 Grade C | SA588 Grade K |
| EN 10025-5 | S235J0W | S235J2W | S355J0WP | S355J2WP |
| S355J0W | S355J2W | S355K2W | ||
| EN 10155 | S235J0W | S235J2W | ||
| S355J0WP | S355J2WP | |||
| S355J0W | S355J2G1W | S355J2G2W | S355K2G1W | |
| S355K2G2W | ||||
| TB/T 1979 | 08CuPVRE | 09CuPTiRE-A | 09CuPTiRE-B | 09CuPCrNi-A |
| 09CuPCrNi-B | 05CuPCrNi | |||
| GB/T 4171 | Q295GNH | Q345GNH | Q265GNH | Q310GNH |
| Q235NH | Q295NH | Q355NH | Q415NH | |
| Q460NH | Q500NH | Q550NH | ||
| JIS G 3114 | SMA400AW | SMA400BW | SMA400CW | |
| SMA400AP | SMA400BP | SMA400CP | ||
| SMA490AW | SMA490BW | SMA490CW | ||
| SMA490AP | SMA490BP | SMA490CP | ||
| SMA570W | SMA570P | |||
| JIS G3125 | SPA-H | SPA-C |
