JIS G3466 Standard Carbon Steel Square Steel Tube with STKR400 and STKR490 Grades in 20 × 20 mm to 350 × 350 mm Dimensions
Product Details
Square Seamless Carbon Steel Tube
,JIS G3466 Seamless Steel Tube
,Carbon Steel Rectangular Tube
JIS G3466 carbon steel square steel tube is a cold-formed or formed structural hollow section used for general civil engineering, architectural, and fabricated steel structures. Under JIS G3466, the standard grade symbols are STKR400 and STKR490; STKR400 is selected for general structural frames, while STKR490 is used when higher yield and tensile strength are required. The tube is normally supplied as-manufactured, with no heat treatment unless otherwise agreed, and inspection covers chemical composition, tensile properties, dimensions, appearance, and marking.
| Item | Specification |
|---|---|
| Material | Carbon steel square hollow section |
| Standard | JIS G3466 |
| Main Grades | STKR400, STKR490 |
| Outside Dimension | Common commercial range: 20 × 20 mm to 350 × 350 mm; custom sizes by agreement |
| Wall Thickness | Common commercial range: 1.2-12.5 mm; heavy-wall options subject to mill capability |
| Length | 1-12 m customizable; common stock lengths include 6 m, 8 m, and 12 m |
| Tolerance Range | Side length ≤100 mm: ±1.5 mm; side length >100 mm: ±1.5%; wall thickness <3 mm: ±0.3 mm; wall thickness ≥3 mm: ±10% |
| Straightness | Maximum 0.3% of total length |
| Surface Condition | Black, oiled, galvanized, painted, or bare finish; surface shall be free from harmful defects |
| Heat Treatment | Normally supplied as-manufactured; heat treatment is generally not applied unless specified |
| Manufacturing Route | ERW, forge-welded, automatic arc welded, or seamless tube formed into square section |
| Property | STKR400 | STKR490 |
|---|---|---|
| Minimum Tensile Strength | 400 MPa | 490 MPa |
| Minimum Yield Point / Proof Stress | 245 MPa | 325 MPa |
| Minimum Elongation | 23% | 23% |
| Carbon Limit | C ≤0.25% | C ≤0.18% |
| Phosphorus / Sulfur Limit | P ≤0.040%, S ≤0.040% | P ≤0.040%, S ≤0.040% |
| Straightness Control | ≤0.3% of total length | ≤0.3% of total length |
JIS G3466 specifies two grades only: STKR400 and STKR490. The values above come from the JIS G3466 grade tables and public technical summaries of the standard.
Professional buyers usually ask whether STKR400 or STKR490 is the correct grade for the design load. We support grade selection by checking the required minimum yield strength: STKR400 provides ≥245 MPa, while STKR490 provides ≥325 MPa. This avoids over-specifying expensive material or under-specifying a load-bearing member.
For welded frames, brackets, railing posts, and modular structures, dimensional mismatch creates assembly problems. We control the key JIS G3466 tolerances: side dimension, wall thickness, squareness, flatness, corner dimension, and straightness. Straightness can be controlled to 0.3% of total length, supporting better cutting, welding, and fixture alignment.
Procurement teams often need mill traceability, heat number control, and inspection documents. JIS G3466 requires marking by grade, dimension, and manufacturer, and a test certificate can be provided when requested; the cited JIS text also references inspection documentation under JIS G 0415.
| Standard System | Reference Standard | Brief Description |
|---|---|---|
| JIS | JIS G3466 | Carbon steel square and rectangular tubes for general structure |
| ASTM | ASTM A500 / A500M | Cold-formed welded and seamless carbon steel structural tubing in round and shaped sections |
| EN | EN 10219 | Cold-formed welded structural hollow sections of non-alloy and fine-grain steels |
| GOST | GOST hollow structural section standards | Used for square and rectangular structural steel tubes in CIS-market procurement |
| GB | GB/T 6728-2025 | Cold forming sectional steel for general structure; current Chinese national standard, implemented March 1, 2026 |
ASTM A500 covers cold-formed welded and seamless carbon steel structural tubing for welded, riveted, or bolted construction of bridges and buildings.
Application product: steel guardrail post for industrial platforms.
JIS G3466 square steel tube is suitable for producing welded guardrail posts where stable section geometry, predictable yield strength, and clean weld fit-up are required.
| Grade | Standard | C max % | Si max % | Mn max % | P max % | S max % | Other |
|---|---|---|---|---|---|---|---|
| STKR400 | JIS G3466 | 0.25 | -- | -- | 0.040 | 0.040 | Other alloying elements may be added if necessary |
| STKR490 | JIS G3466 | 0.18 | 0.55 | 1.50 | 0.040 | 0.040 | Other alloying elements may be added if necessary |
| ASTM A500 Grade B | ASTM A500 | 0.26 heat / 0.30 product | -- | 1.35 heat / 1.40 product | 0.035 heat / 0.045 product | 0.035 heat / 0.045 product | Cu ≥0.20% when copper steel is specified |
| ASTM A500 Grade C | ASTM A500 | 0.23 heat / 0.27 product | -- | 1.35 heat / 1.40 product | 0.035 heat / 0.045 product | 0.035 heat / 0.045 product | Cu ≥0.20% when copper steel is specified |
| S355J2H | EN 10219 | 0.22 | 0.55 | 1.60 | 0.030 | 0.030 | CEV ≤0.45%; impact requirement at -20°C |
| Grade | Standard | Yield Strength / Proof Stress | Tensile Strength | Elongation | Notes |
|---|---|---|---|---|---|
| STKR400 | JIS G3466 | ≥245 MPa | ≥400 MPa | ≥23% | No. 5 test piece, tube axis direction |
| STKR490 | JIS G3466 | ≥325 MPa | ≥490 MPa | ≥23% | No. 5 test piece, tube axis direction |
| ASTM A500 Grade B, shaped tube | ASTM A500 | ≥317 MPa | ≥400 MPa | ≥23% | Square/rectangular structural tubing |
| ASTM A500 Grade C, shaped tube | ASTM A500 | ≥345 MPa | ≥425 MPa | ≥21% | Square/rectangular structural tubing |
| S355J2H | EN 10219 | ≥355 MPa for t ≤16 mm; ≥345 MPa for 16| 510-680 MPa for t≤3 mm; 470-630 MPa for 3 | ≥20% |
KV2 ≥27 J at -20°C |
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