JIS G3101: Rolled Steel for General Structure — SS400, SS490, SS540

Quick Answer

JIS G3101 (溶接構造用圧延鋼材 — hot-rolled steel for general structure) is one of Japan's most widely used structural steel standards. Issued by the Japanese Industrial Standards Committee, it covers plates, flat bars, shapes (H, I, channel, angle), and sheet piling rolled from carbon steel. JIS mill certificates for G3101 material may be issued in Japanese only or in bilingual Japanese/English format depending on the mill and the export destination — Western engineers receiving Japanese-only certificates should refer to the field translation guide at [/standards/jis-mill-cert-guide].

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Scope and Applicability

JIS G3101 applies to hot-rolled steel products intended for:

• General structural fabrication (buildings, bridges, machinery frames)
• Bolted and riveted connections
• Applications where weldability assurance is not a primary requirement (for welded structures, JIS G3106 SM grades are preferred)
• Structural sections and sheet piling

The standard does not cover pressure vessels, boilers, or applications requiring guaranteed notch toughness at low temperature. For those applications, JIS G3106 (welded structure) or JIS G3115 (pressure vessels) should be specified.

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Scope and Applicability

G3101 applies to the following product forms:

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JIS Grade Designation System

JIS structural steel grade names follow a simple pattern:

• SS = Structural Steel (一般構造用 — general structural use)
• Number = minimum tensile strength in MPa (N/mm²)

Thus SS400 means "structural steel, minimum tensile strength 400 MPa." This convention contrasts with ASTM grades (which use a yield strength number, e.g., A572 Grade 50 = 50 ksi yield) and EN grades (which also use yield strength, e.g., S235 = 235 MPa yield). When comparing grades across standards, always verify which strength metric the grade number represents.

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Grade Coverage

SS400 is by far the most common grade and is the Japanese equivalent often cited in lieu of ASTM A36 in Asia-Pacific construction.

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Chemical Composition Requirements

All values are wt% maximum unless noted. Ladle (heat) analysis applies.

Key note — no carbon limit for SS330, SS400, SS490: Unlike ASTM A36 (C ≤ 0.26%) or EN S235JR (C ≤ 0.17%), JIS G3101 imposes no maximum carbon content for the three lower grades. Only phosphorus and sulfur are controlled. This is the single most important compositional distinction Western engineers must understand:

• SS400 from one Japanese mill may have C ≈ 0.12% while material from another mill meeting the same standard may have C ≈ 0.24%
• Preheat requirements for welding cannot be reliably calculated from the grade designation alone
• For welded applications, G3106 SM grades (which do specify carbon and CEV limits) are strongly preferred

SS540 is the only G3101 grade with carbon, manganese, and silicon limits, reflecting the higher strength level achieved through microalloying or higher carbon.

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Mechanical Properties

Yield strength varies by product thickness. UTS and elongation apply to all thicknesses within each grade unless noted.

SS330

SS400

SS490

SS540

Elongation gauge length: 5.65√A₀ (proportional gauge length) for plates; 50 mm for thin sheet.

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Impact Test Requirements

JIS G3101 does not require Charpy impact testing for any grade. This is a key limitation compared to JIS G3106, where B and C sub-grades require verified notch toughness. For applications requiring impact assurance (e.g., structures in cold climates or dynamic loading), specify G3106 SM grades with C sub-grade designation.

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Bend Test Requirements

A bend test is required as part of the standard acceptance criteria:

The test piece must not show cracks or flaws on the outer surface after bending.

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JIS Mill Certificate Format

JIS G3101 material is supplied with an inspection certificate conforming to JIS Z 2242 (test piece) and issued under one of the following inspection certificate types:

For export to Europe, a JIS 3.1B certificate is typically accepted in place of EN 10204 3.1. For projects where EN 10204 3.2 is contractually required, a JIS 3.2 certificate must be specified at order stage — most Japanese mills can arrange this with advance notice.

A typical JIS G3101 mill certificate will show:

1. 規格 (Standard): JIS G3101
2. 鋼種 (Steel grade): SS400 (or other)
3. 熱番号 (Heat number): e.g., 2B1234A
4. 寸法 (Dimensions): thickness × width × length in mm
5. 化学成分 (Chemical composition): P and S values; C/Mn/Si may be reported voluntarily
6. 機械的性質 (Mechanical properties): YS, UTS, elongation, bend test result
7. 合格 stamp or signature confirming conformance

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Cross-Standard Equivalents

SS400 is often described as equivalent to ASTM A36 and EN S235JR, but these equivalences are approximate. The absence of a carbon limit in SS400 means the match is mechanical-property-based only.

All equivalences are approximate and for guidance only. Chemical composition profiles differ significantly, particularly for SS400 vs. A36/S235JR which have explicit carbon limits.

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MTC Verification Checklist

When verifying a JIS G3101 mill test certificate:

• Standard designation confirms JIS G3101 (not G3106 or another standard)
• Grade (鋼種) matches purchase order — SS400, SS490, etc.
• Heat number (熱番号) is legible and traceable to bundle/plate markings
• Tensile strength (引張強さ) falls within the specified range for the grade
• Yield strength (降伏点 or 耐力) meets the minimum for the supplied thickness
• Elongation (伸び) meets or exceeds the minimum
• Bend test (曲げ試験) shows no cracks — result stated as 合格 (passed)
• P and S values reported; confirm both are ≤ 0.050%
• If C is reported voluntarily, note the value for weld preheat calculation
• Certificate type (3.1B, 3.2, etc.) matches contractual requirement
• Mill stamp or authorized signature present

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Frequently Asked Questions