JIS G 3136 SN490B Structural Steel: Procurement & Technical FAQ Guide

Part 1: Standard & Material Selection

Q1: What is the core definition of JIS G 3136 SN490B?

A: It is a high-performance structural steel grade specified under the Japanese Industrial Standard (JIS) G 3136, designed specifically for building structures. It is engineered for critical load-bearing members, such as beams and columns in 

high-rise or large-span buildings, offering superior seismic resistance and weldability.

Q2: Why does the yield point requirement change based on thickness?

A: The standard recognizes the "thickness effect," where the mechanical properties change due to rolling and cooling processes. For instance, the yield point for plates 6mm to 12mm thick is ≥ 325 MPa, while it ranges from 295 to 415 MPa for plates over 

40mm thick. Adhering to these thickness-specific requirements is essential to ensure structural safety.

Part 2: Procurement & Equivalency

Q3: Can SN490B be directly swapped with other international grades (e.g., ASTM A36 or EN S355)?

A: We advise against direct substitution without professional engineering approval. While other grades may have similar tensile strengths, SN490B has specific requirements for yield ratios and chemical composition (such as controlled 

carbon equivalents) essential for seismic energy absorption. Always verify with the project’s structural engineer whether an alternative meets the design's seismic redundancy and welding requirements.

Q4: Does JIS G 3136 only cover steel plates?

A: No, the standard applies to various hot-rolled steel products, including plates, sections (shapes), and strips. When requesting a quotation, please specify whether you require plates or specific structural sections to ensure the material matches your construction drawings.

Part 3: Quality Control & Field Inspection

Q5: What are the professional tips for measuring thickness during on-site inspection?

A: To ensure accurate readings, avoid measuring directly over the burrs created by the cutting process, as these can lead to false high readings. Instead, measure at multiple points on a flat surface approximately 20-50mm away from the cut edge and calculate the average.

Q6: How can I verify the authenticity of the material upon receipt?

A: Verification should rely on strict cross-referencing of documentation and physical marking.

Traceability: Always compare the Heat Number listed on the Mill Test Certificate (MTC) against the physical stamp marked directly on the steel plate.

Chemical Compliance: Ensure the batch results provided in the MTC strictly adhere to the limits defined by the JIS G 3136 standard, particularly for Phosphorus (P) and Sulfur (S).

Expert Verification: If any discrepancy arises between the test results and the physical material, we recommend conducting a third-party laboratory analysis to confirm that critical elements—such as Carbon (C), Silicon (Si), and Manganese (Mn)—fall within the required tolerance range.