​

1. Balance between high strength and weight：

"490" indicates that its minimum yield strength is 490 MPa. This is a rather high strength level, meaning it can withstand a large load without permanent deformation. This enables the use of thinner or smaller-sized steel pipes while achieving the same structural strength, thereby achieving the purpose of reducing weight and saving materials.

2. Excellent cold bending workability:

Although it has high strength, the chemical composition of STKR490 steel pipe has been specially designed to ensure that it has excellent cold bending and cold forming performance. This is crucial for mechanical components that require secondary processing such as bending, flaring and shrinking.

3. Clear purpose positioning:

The full name of the standard is "Carbon Steel Pipes for Mechanical Structures". This means it is not used for transporting fluids (that is a fluid pipe, such as STPG), nor for building structures (that is a structural pipe, such as STK). It is specially designed for manufacturing components such as frames, chassis, booms, connecting rods, various pins and sleeves of mechanical equipment.

4. Welding performance:

As a welded steel pipe, its base material itself has good weldability. Meanwhile, it is also manufactured through various welding processes (such as arc welding, resistance welding, etc.), and thus is highly suitable for subsequent welding and assembly.

Main requirements (in accordance with JIS G3466 standard)

The requirements of the standard for STKR490 steel pipes are mainly reflected in the following aspects:

1. Chemical Composition (Smelting Analysis)

The chemical composition of steel pipes is the basis for ensuring their mechanical properties and processing performance. The typical component requirements of STKR490 are as follows:

• Carbon (C) : Generally no more than 0.20%. A lower carbon content helps ensure its weldability and cold bending property.
• Manganese (Mn) : It has a relatively high content and is one of the main elements for enhancing strength.
• Phosphorus (P) and sulfur (S) : As impurity elements, their contents are strictly limited to a relatively low level (for example, P≤0.030%, S≤0.030%) to ensure toughness and processing performance.

Note: The specific range of components may vary slightly depending on the manufacturer and different processes, but it must meet the mechanical properties specified in the standard.

2. Mechanical properties - This is the most crucial requirement

• Yield strength (σs) : ≥490 MPa. This is the origin of the name and the core indicator of this grade.
• Tensile strength (σb) : ≥610 MPa. Represents the maximum stress that the material can withstand before being pulled apart.
• Elongation (δ) : ≥17%. When measuring the plastic deformation capacity of a material, the higher the elongation rate, the softer the material is and the less likely it is to undergo brittle fracture.

3. Process performance and tests

Flattening test:

A section of steel pipe is flattened in a direction perpendicular to the axis until the distance between the two inner walls reaches the specified value (for example, for welded pipes, it is three times the thickness of the pipe wall). After the test, there shall be no cracks or fractures in the weld seam and the base material. This is an important method for testing its plasticity and welding quality.

Bending test:

For small-diameter pipes, a bending test may be conducted instead of a flattening test, and it is also required that there be no cracks.

Non-destructive testing:

Eddy current testing (ET) or other non-destructive testing is usually carried out on the weld seam to ensure its continuity and defect-free nature.

4. Dimensional and shape tolerances

The standard clearly stipulates the allowable deviations for the outer diameter, wall thickness, length, out-of-roundness, and curvature of steel pipes to ensure their assembly accuracy as mechanical parts.

5. Delivery status

It is usually delivered in the original rolled condition (black pipe, uncoated) or galvanized condition. Most mechanical structural tubes are delivered in black form and then undergo subsequent treatments such as painting and electroplating by the manufacturer.

Comparison with other common steel pipes

Summary and application suggestions

JIS G3466 STKR490 is a kind of high-strength welded structural tube with excellent performance, especially suitable for manufacturing mechanical components that require a balance of strength, lightweight and good processability.

When making purchases and conducting acceptance inspections, you should focus on:

1. Material Certification (MTC) : Ensure that the supplier provides a material certificate that complies with the JIS G3466 standard, and verify the mechanical properties (especially yield strength and tensile strength) and chemical composition.
2. Visual inspection: Check the surface for any major scratches, pits or rust.
3. Dimensional verification: Sample and check whether the outer diameter and wall thickness are within the tolerance range.
4. Application considerations: If your product requires subsequent cold bending, stamping and other processing, it is necessary to emphasize to the supplier the requirements for cold working performance. If it is used for dynamic loads or critical safety components, more stringent flaw detection requirements may need to be added