1. Introduction
JIS SS400 is one of the most widely used structural carbon steel grades in Asia, particularly in Japan, where it originates. It is defined by the Japanese Industrial Standards (JIS) and is a low carbon, mild steel that offers excellent weldability, machinability, and formability, making it a versatile choice for a wide range of structural and fabrication applications.
SS400 is comparable to European and American structural steels like EN S235JR and ASTM A36, making it a reliable global option in steel design.
2. What Is JIS SS400 Steel?
SS400 is a structural grade carbon steel defined under the JIS G3101 standard. The “SS” stands for “Structural Steel”, and “400” denotes its minimum tensile strength of 400 MPa.
It is typically supplied as:
- Hot rolled sheets and plates
- Beams and channels
- Angles and bars
- Coils and strips
Key Characteristics:
- Mild carbon content
- Excellent weldability
- Affordable and widely available
- Good strength-to-weight ratio
GengFei JIS SS400 Carbon Steel
3. SS400 and the JIS G3101 Standard
JIS G3101:
This is the Japanese Industrial Standard that specifies:
- Hot rolled steel for general structural use
- Covers SS330, SS400, SS490, and SS540 grades
- Defines chemical and mechanical requirements, dimensional tolerances, and testing methods
SS400 is the most commonly used grade in this family.
4. Chemical Composition
Below is the typical chemical composition of SS400 according to JIS G3101:| Element | Maximum Content (%) |
|---|---|
| Carbon (C) | ≤ 0.25 |
| Manganese (Mn) | ≤ 1.40 |
| Phosphorus (P) | ≤ 0.050 |
| Sulfur (S) | ≤ 0.050 |
5. Mechanical Properties
| Property | Value |
|---|---|
| Yield Strength (MPa) | ≥ 245 (thickness ≤ 16mm) |
| Tensile Strength (MPa) | 400 – 510 |
| Elongation (%) | ≥ 21 (for plates ≤ 25mm) |
| Hardness (Brinell) | ~120 – 160 HB |
| Modulus of Elasticity | ~200 GPa |
6. Equivalent Grades Comparison
| Standard | Grade | Remarks |
|---|---|---|
| JIS G3101 | SS400 | Japanese Standard |
| ASTM | A36 | Similar mechanical properties |
| EN 10025 | S235JR | European equivalent |
| GB/T 700 | Q235B | Chinese equivalent |
| ISO | Fe360B | International approximation |
7. Sub-Grades and Designations
SS400 may sometimes be designated with additional symbols for product form:| Designation | Meaning |
|---|---|
| SS400B | Rolled steel for general structure |
| SS400C | Steel plates and strips |
| SS400D | Steel bars |
| SS400E | Enhanced weldability |
8. Forms and Dimensions
SS400 is available in various product forms:| Product Form | Typical Dimensions |
|---|---|
| Hot Rolled Coils | 1.2 mm – 25 mm thickness |
| Steel Plates | Up to 2000 mm width |
| I-Beams and Channels | Standard lengths (6–12 m) |
| Angles | Equal/unequal angles, various sizes |
| Flat Bars | 10 × 3 mm to 300 × 25 mm |
9. Manufacturing Process
SS400 steel is typically produced using the Basic Oxygen Furnace (BOF) or Electric Arc Furnace (EAF) methods, followed by:
- Hot rolling into coils, plates, or shapes
- Cooling in open air
- Surface treatments (optional) like pickling or oiling
10. Welding, Machinability, and Formability
Welding
- Excellent weldability
- Suitable for MIG, TIG, SMAW, and FCAW
- No preheating required under standard conditions
Machinability
- Easy to cut, drill, and mill
- Works well with both CNC and manual equipment
Formability
- Can be bent, punched, and shaped
- Ideal for press-brake forming and roll forming
11. Surface Finishes
| Finish Type | Description |
|---|---|
| Mill Finish | As-rolled surface, untreated |
| Pickled & Oiled (P&O) | Cleaned of oxides and rust, coated with oil |
| Galvanized | Zinc coating for corrosion resistance |
| Painted or Primed | For enhanced weather resistance |
12. SS400 vs. Other Mild Steels
| Property | SS400 | ASTM A36 | S275JR |
|---|---|---|---|
| Yield Strength | ≥ 245 MPa | ≥ 250 MPa | ≥ 275 MPa |
| Weldability | Excellent | Excellent | Good |
| Availability | Widely used in Asia | North America | Europe |
| Cost | Low | Low | Medium |
13. Applications of SS400 Steel
Construction
- Steel frames and columns
- Prefabricated buildings
- Roofing support and scaffolding
Manufacturing
- Equipment frames and machine bases
- Sheet metal components
- Storage racks and platforms
Automotive
- Trailer chassis and parts
- Industrial vehicles
Infrastructure
- Bridges and guardrails
- Towers and support structures
Others
- Agricultural equipment
- Containers and enclosures
- Shipbuilding (non-critical components)
14. Benefits of SS400
✅ Low cost and widely available
✅ Excellent weldability and machinability
✅ Good mechanical strength for general use
✅ Flexible for cold and hot forming
✅ Supplied in many shapes and sizes
15. Limitations and Considerations
⚠️ Not suitable for highly corrosive environments without coating
⚠️ No notch toughness guarantees
⚠️ Not ideal for pressure vessels or critical safety parts
⚠️ Yield strength lower than high-strength low-alloy (HSLA) steels
16. Frequently Asked Questions (FAQs)
Q1: Is SS400 magnetic?
Yes. SS400 is a ferrous material and shows magnetic properties.
Q2: Can SS400 be used outdoors?
Yes, but it must be galvanized or painted to prevent rust.
Q3: What welding method is best for SS400?
Any standard welding technique (MIG, TIG, SMAW) works well without preheating.
Q4: How does SS400 compare to Q235?
Both are very similar in composition and performance. Q235 is the Chinese counterpart.
Q5: Does SS400 meet international standards?
Yes, it’s widely accepted in Asian and global markets, but always cross-check with ASTM or EN equivalents if needed.
17. Conclusion
JIS SS400 steel is a foundational material in the structural steel industry, particularly in Asia and global export markets. Its low cost, good strength, weldability, and availability in various forms make it a go-to choice for construction, manufacturing, and infrastructure applications.
Whether you are sourcing hot-rolled coils for sheet metal fabrication, or I-beams for building construction, SS400 offers dependable performance and easy workability—all while keeping costs in check.
Gengfei Provides High Quality JIS SS400 Carbon Steel
Please let us know your procurement requirements, and we will quickly tailor the most competitive quotation for you.
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