SS490 is a general structural hot-rolled steel defined by the Japanese Industrial Standard (JIS G 3101).
Here's a detailed breakdown of what this material is, its properties, and its equivalents.
1. Decoding the Designation "SS490"
SS: Stands for "Steel Structure". This prefix indicates it is a general structural rolled steel.
490: Indicates the minimum tensile strength in MPa. Therefore, SS490 must have a tensile strength (TS or Rm) of ≥ 490 MPa.
Important Note: Unlike some standards (like the Chinese Q-series or European S-series), the number in JIS SS grades refers to tensile strength, NOT yield strength.
2. Key Material Properties (Based on JIS G 3101)
Tensile Strength (Rm): ≥ 490 MPa
Yield Strength (ReH): ≥ 325 MPa (This is the critical design strength value).
Elongation: Minimum required varies with thickness (typically around 17-21%).
Chemical Composition: JIS G 3101 does not specify precise chemical requirements for SS grades. The focus is on achieving the required mechanical properties, making it a carbon-manganese steel with a typical carbon content (C) of ≤ 0.30%.
Condition: Supplied in the as-rolled (hot-rolled) condition.
3. Comparison to Common Steels
vs. SS400: SS490 is a higher-strength version of the most common Japanese mild steel, SS400 (TS ≥ 400 MPa, YS ≥ 245 MPa).
vs. Chinese Q355 (Old Q345): SS490 is very similar in strength level. Q355B has a yield strength of ≥ 355 MPa and a tensile strength of 470-630 MPa. SS490 has a slightly higher minimum tensile strength (490 MPa) but a slightly lower specified yield strength (≥325 MPa). In practice, they are often considered commercial equivalents for many applications.
vs. European S355 (e.g., S355JR): S355JR is defined by its minimum yield strength of 355 MPa, with tensile strength typically between 470-630 MPa. SS490 is mechanically very close and widely used as an equivalent.
vs. ASTM A36/A572-50: SS490's strength sits between these common American grades.
A36: Lower strength (YS ≥ 250 MPa, TS 400-550 MPa).
A572 Gr.50: More direct equivalent (YS ≥ 345 MPa, TS ≥ 450 MPa).
4. Common International Equivalents
| Standard (Country/Region) | Common Equivalent Grade | Key Difference/Note |
|---|---|---|
| JIS (Japan) | SS490 (Base Grade) | Defined by Tensile Strength (≥490 MPa). |
| GB/T (China) | Q355B (GB/T 1591) | Closest match. Defined by Yield Strength (≥355 MPa). |
| EN (Europe) | S355JR (EN 10025-2) | Closest match. Defined by Yield Strength (≥355 MPa). |
| ASTM (USA) | A572 Grade 50 | Very close. A36 is weaker but sometimes substituted. |
| DIN (Germany - Old) | St52-3 | Historical equivalent (now replaced by S355JR). |
5. Primary Applications
SS490 is a versatile, medium-strength structural steel used widely in:
Building and Bridge Construction: For frames, beams, columns, and trusses.
General Machinery and Equipment: Frames, bases, supports.
Industrial Vehicles: Chassis components, truck frames, trailer parts.
Shipbuilding: For non-critical structural parts (hull plates typically use higher-spec shipbuilding steel).
Storage Racks and Agricultural Equipment.
6. Key Considerations
Weldability: Good, due to its moderate carbon content. Standard welding procedures apply.
No Impact Requirement: Standard SS490 has no mandatory Charpy impact toughness requirement. For applications requiring low-temperature toughness, other JIS grades like SM490 (JIS G 3106) or S355 with quality grades (J, K, etc.) must be specified.
Formability: It has moderate formability but is less ductile than lower-strength steels like SS400.
Summary:
SS490 is a Japanese standard hot-rolled structural steel with a minimum tensile strength of 490 MPa. It is a general-purpose, medium-strength steel widely used in construction and machinery, comparable to international grades like China's Q355B and Europe's S355JR. Its main advantage is a good balance of strength, weldability, and cost. For critical dynamic or low-temperature applications, more specialized grades with guaranteed toughness should be considered.