ASME SA588 Grade K is a high-strength, low-alloy structural steel designed for enhanced atmospheric corrosion resistance. Often referred to as Corten-B or weathering steel, it forms a protective, rust-like patina that eliminates the need for painting. It is commonly used in bridges, buildings, and outdoor structures to reducemaintenance.
ASME SA588 Grade K Weathering Resistant Steel specifications:
Thickness: 3mm--150mm
Width: 30mm--4000mm
Length: 1000mm--12000mm
SA588 Grade K Weathering steel chemical composition
|
Grades |
C max |
Mn |
P max |
S max |
Si |
Ni max |
Cr |
Cu |
V |
|
SA588GR.K |
0.20 |
0.75-1.35 |
0.04 |
0.05 |
0.15-0.50 |
0.50 |
0.40-0.70 |
0.20-0.40 |
0.01-0.10 |
SA588 Grade K Weathering resistant steel tensile property request
|
ASME SA588 Grade K |
Plates and bars |
Structural shapes |
||
|
|
＜100mm |
≥100-125mm |
＞125-200 |
|
|
Tensile strength min MPa |
485 |
460 |
435 |
485 |
|
Yield strength min MPa |
345 |
315 |
290 |
345 |
|
Elongation min |
21 |
21 |
21 |
21 |
Technical Comparison: A588 Grade K vs. Grade A & B
To help purchasers understand the nuances, we compare the three most common grades under the ASTM A588 standard.
| Feature | A588 Grade K | A588 Grade A | A588 Grade B |
| Common Thickness | Up to 8" (200mm) | Up to 4" (100mm) | Up to 8" (200mm) |
| Silicon (Si) | 0.15% - 0.50% | 0.30% - 0.65% | 0.15% - 0.50% |
| Chromium (Cr) | 0.40% - 0.70% | 0.40% - 0.65% | 0.40% - 0.70% |
| Nickel (Ni) | ≤ 0.50% | ≤ 0.40% | ≤ 0.50% |
| Yield Strength | 50 ksi (345 MPa) | 50 ksi (345 MPa) | 50 ksi (345 MPa) |
| Primary Advantage | Optimized for specific heavy-section corrosion resistance. | The standard for general construction. | Optimized for thicker structural plates. |
Key Insight: While the yield strength is identical (50 ksi), Grade K features a specialized alloying range (particularly for Cr and Ni) that engineers often specify for high-performance structural designs where the long-term stability of the patina in specific micro-climates is critical.
Read More About A588 GR A Case>>>
ASTM A588 Grade K vs. ASME SA588 Grade K
In the steel industry, the difference between "ASTM" and "ASME" is primarily about regulatory jurisdiction rather than material composition.
ASTM A588 Grade K: Governed by the American Society for Testing and Materials. It is the standard used for general civil engineering, architecture, and structural projects (e.g., buildings, sculptures, facades).
ASME SA588 Grade K: Governed by the American Society of Mechanical Engineers. The "S" prefix indicates it has been adopted into the ASME Boiler and Pressure Vessel Code (BPVC).
| Feature | ASTM A588 Grade K | ASME SA588 Grade K |
| Primary Use | General structural and architectural use. | Pressure vessels, boilers, and nuclear components. |
| Technical Content | Identical chemical and mechanical properties. | Identical to ASTM, but must comply with ASME Section II. |
| Compliance | Civil engineering codes (AISC). | Pressure vessel codes (ASME BPVC). |
Summary for Purchasers: For 99% of architectural and landscape projects, ASTM A588 Gr.K is the correct specification. ASME SA588 Gr.K is only required if the steel is part of a pressurized system or boiler.
Comparison Table: ASME SA588 Gr.K vs. ASTM A709 Gr.50W
This is the most frequent comparison in Bridge Engineering. While SA588 Gr.K is a general high-strength weathering steel, A709 Gr.50W is specifically designed for bridge infrastructure.
| Comparison Criteria | ASME SA588 Grade K | ASTM A709 Grade 50W |
| Standard Scope | High-Strength Structural Steel (General). | Structural Steel for Bridges (Specialized). |
| Yield Strength | 50 ksi (345 MPa) | 50 ksi (345 MPa) |
| Corrosion Index (I) |
≥6.0≥6.0 (per ASTM G101) |
≥6.0≥6.0 (per ASTM G101) |
| Impact Testing (CVN) | Optional. (Only if Supplementary Requirement S5 is ordered). | Mandatory. Must meet Charpy V-Notch requirements based on Temperature Zones. |
| Fracture Critical (FC) | Not specifically defined for fatigue. | Includes specific provisions for Fracture Critical members. |
| Thickness Range | Up to 8" (200mm) | Varies by bridge component design. |
| Typical Application | Buildings, Facades, High-load structures. | Highway Bridges, Rail Bridges, Overpasses. |
| Certification | Standard MTC. | Often requires "Dual Certification" (A588 + A709). |
What Purchasers Care About: Addressing Core Concerns
When a client asks for Grade K, they are usually involved in high-load, heavy-section engineering. Here is how we address their specific doubts:
■ Structural Safety & "Dual Certification"
Purchasers in bridge engineering often worry about Brittle Fracture.
The Solution: We provide SA588 Gr.K that is Dual Certified to meet ASTM A709 Gr.50W. This means the material has undergone mandatory CVN (Charpy V-Notch) Impact Testing at -20°C or -40°C, ensuring it won't crack under winter loads.
■ The Corrosion Performance (Atmospheric Stability)
Purchasers need proof that the "Weathering" claims are scientifically valid.
The Solution: We provide Mill Test Certificates (MTC) that show the exact chemical balance of Cu, Cr, Ni, and P. We calculate the G101 Corrosion Index for every batch to ensure it exceeds 6.0, guaranteeing a 50+ year service life without painting.
■ Aesthetics & Environmental Protection (The "Rust Bleeding" Pain Point)
For architectural projects (Facades, Sculptures), the biggest fear is Rust Runoff staining the surroundings.
The Solution: We offer two essential processing services:
Pre-Rusting: We use a proprietary oxidation process to create a uniform, deep-brown patina in 48 hours.
Rust Sealing/Fixing: We apply a professional sealant that "locks" the rust layer, preventing "rust tears" from staining stone or concrete foundations.
■ Weldability and Matching Consumables
Purchasers worry that the weld seams will rust a different color than the plates.
The Solution: We provide Matching Weathering Consumables (Ni-Cu alloyed welding wires). This ensures that the weld joints develop the same protective patina and color as the SA588 Gr.K base metal.
If your project is a Building or Facade, order ASTM A588 Grade K. If your project is a Bridge or Highway Infrastructure, ensure you specify ASTM A709 Grade 50W (or Dual Certified A588 Gr.K) to guarantee the impact toughness required by safety codes.
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