JIS G3445 STKM 14A Cold Drawn Carbon Steel Seamless Tubes For Machine Structure
JIS G3445 STKM 14A Cold-Drawn Carbon Steel Seamless Tube for Machine Structure
Material
This product is a cold-drawn seamless carbon steel tube manufactured according to the JIS G3445 standard, grade STKM 14A, intended for structural and mechanical (machine) uses. It is used where precise dimensions, good surface finish, and adequate mechanical strength are required.
Specifications
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Form: Seamless tube, cold drawn (or cold worked)
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Standard: JIS G3445
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Grade: STKM 14A
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Outer diameter (OD) range: typically in the range ~ 6 mm to ~ 219.1 mm (depending on supplier)
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Wall thickness: ~ 0.5 mm to ~ 10 mm (varies per supplier)
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Length: single random, double random, or as ordered (max length ~ 10 m typical)
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Surface finish: cold‐drawn, cleaned, deburred or chamfered if required
Chemical Composition
Below is a comparative table of chemical composition limits (mass fractions, %) for STKM16 series of JIS G3445 (including 14A and four other nearby grades) for reference:
| Grade | C (max) | Si (max) | Mn (range) | P (max) | S (max) |
|---|---|---|---|---|---|
| STKM 14A | ≤ 0.30 | ≤ 0.35 | 0.30 – 1.00 | ≤ 0.040 | ≤ 0.040 |
| STKM 13A | ≤ 0.25 | ≤ 0.35 | 0.30 – 0.90 | ≤ 0.040 | ≤ 0.040 |
| STKM 13C | ≤ 0.25 | ≤ 0.35 | 0.30 – 0.90 | ≤ 0.040 | ≤ 0.040 |
| STKM 12A | ≤ 0.20 | ≤ 0.35 | ≤ 0.60 | ≤ 0.040 | ≤ 0.040 |
| STKM 15A | 0.25 – 0.35 | ≤ 0.35 | 0.30 – 1.00 | ≤ 0.040 | ≤ 0.040 |
Mechanical Properties
Below is a table of the mechanical (minimum) properties for STKM14A and four related grades, per JIS G3445 specification:
| Grade | Tensile Strength, Rm (MPa, min) | Proof / Yield, Rp0.2 (MPa, min) | Elongation, A (%) (min) | Remarks / Other Tests |
|---|---|---|---|---|
| STKM 14A | ≥ 410 MPa | ≥ 245 MPa | ≥ 25 % | Flattening & bending tests (3/4 D, 90°, 6 D) |
| STKM 13A | ≥ 375 MPa | ≥ 215 MPa | ≥ 30 % | — |
| STKM 13C | ≥ 510 MPa | ≥ 380 MPa | ≥ 15 % | — |
| STKM 12A | ≥ 345 MPa | ≥ 175 MPa | ≥ 35 % | — |
| STKM 15A | ≥ 470 MPa | ≥ 275 MPa | ≥ 22 % | — |
Main Features
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High strength and ductility: The grade offers a good balance of tensile strength and elongation, suitable for structural service under load.
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Good machinability and surface finish: Cold drawing process provides fine tolerances and improved surface quality.
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Dimensional precision: The standard mandates strict OD and wall thickness tolerances when cold drawn.
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Structural stability & robustness: The seamless nature avoids welded seam weaknesses.
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Versatile processing: It can be further processed (surface finishing, bending, forming) under agreed conditions.
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Cost-effective: In many mechanical applications, STKM grades provide sufficient performance without resorting to more expensive alloy steels.
Applicable Standards
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JIS G3445 — carbon steel tubes for machine structural purposes (the governing Japanese standard for these STKM grades).
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In comparison or for cross-reference (for equivalence), some grade tables cite similarities to ASTM/other designations, but STKM 14A is a JIS-specific grade (equivalents must be validated).
Application Domains
General application areas
This kind of tube is broadly used in machinery, automotive, bicycles, furniture, appliances, and general mechanical components where a tube with good strength, rigidity, and precision is needed.
Specific uses within those domains
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Machinery: shafts, guide tubes, structural frames, pivot supports
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Automotive: frame support members, structural braces, linkage components
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Bicycles: frame tubes, fork elements, supports
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Furniture / appliances: structural tubing in racks, supports, column rods
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Hydraulic / pneumatic cylinder rods / casings (where exact inner/outer diameters and strength are needed)
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General engineering components: in jigs, fixtures, tool supports, etc.
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