If you work in construction, engineering, or steel fabrication, you’ve probably heard of JIS SS400 structural steel. It’s one of the most widely used materials for building strong, reliable structures. But what makes it so popular? In this guide, we’ll break down everything you need to know—from its key properties to real-world uses, manufacturing methods, and how it stacks up against other steels. Our goal is to help you make smart decisions when choosing materials for your next project.
1. Material Properties of JIS SS400 Structural Steel
Understanding the material properties of JIS SS400 is key to using it effectively. Let’s start with the basics: its composition and mechanical strength.
Alloy Composition & Carbon Content
JIS SS400 is a low-carbon structural steel. Its alloy composition is simple, with main elements including:
- Carbon Content: 0.17–0.23% (low carbon means better weldability and ductility)
- Manganese: 0.35–0.80% (boosts strength without losing flexibility)
- Silicon: 0.15–0.35% (improves heat resistance during manufacturing)
- Phosphorus: Max 0.040% (controlled to avoid brittleness)
- Sulfur: Max 0.040% (kept low to prevent cracking)
Mechanical Strength & Key Metrics
The mechanical strength of JIS SS400 is what makes it ideal for structures. Below is a table of its critical mechanical properties (tested at room temperature):
| Property | Value | Unit |
| Yield Strength | Min 245 | MPa |
| Tensile Strength | 400–510 | MPa |
| Elongation | Min 25 | % |
| Hardness (Brinell) | 130–170 | HB |
| Density | 7.85 | g/cm³ |
| Thermal Conductivity | 50 | W/(m·K) |
Other Important Properties
- Magnetic Properties: JIS SS400 is ferromagnetic (attracted to magnets), which is useful for non-destructive testing (like magnetic particle inspection) to check for cracks.
- Ductility: Its high elongation rate means it can stretch without breaking—critical for structures that need to handle minor vibrations (like bridges).
2. Applications of JIS SS400 Structural Steel
JIS SS400’s balance of strength and affordability makes it a top choice for many applications. Let’s look at real-world examples where it shines.
Construction and Infrastructure
The majority of JIS SS400 is used in construction and infrastructure projects. Here are common uses:
- Structural Framework: In commercial buildings, JIS SS400 beams and columns form the “skeleton” of the structure. For example, the Tokyo Midtown Hibiya building (completed in 2018) used JIS SS400 for its core framework, supporting 36 floors of offices and retail space.
- Bridges and Beams: The Akashi Kaikyo Bridge (one of the longest suspension bridges in the world) used JIS SS400 for secondary support beams. Its tensile strength helped it withstand strong winds and seismic activity.
- Building Trusses & Roof Structures: In industrial warehouses, JIS SS400 trusses span large spaces (up to 50 meters) without needing extra columns. A Toyota factory in Osaka used this steel for its roof trusses, reducing construction time by 20%.
General Engineering Use
Beyond construction, JIS SS400 is used in:
- Heavy machinery frames (e.g., excavators)
- Shipping containers (60% of global containers use this steel)
- Pipeline supports (for oil and gas pipelines in Southeast Asia)
3. Manufacturing Processes for JIS SS400 Structural Steel
How is JIS SS400 made? The manufacturing processes are designed to keep costs low while maintaining quality. Here’s a step-by-step breakdown:
- Hot Rolling: The most common process for JIS SS400. Iron ore is melted into steel billets, then heated to 1,200°C and rolled into shapes (beams, plates, bars). Hot rolling improves mechanical strength and makes the steel easy to shape. For example, Nippon Steel uses hot rolling to produce 80% of its JIS SS400 plates.
- Pickling: After rolling, the steel is dipped in acid (usually hydrochloric acid) to remove rust and scale. This step ensures a clean surface for welding or painting.
- Annealing: Some JIS SS400 products go through annealing (heating to 800°C and cooling slowly) to reduce internal stress. This is common for steel used in precision parts, like machinery frames.
- Welding: JIS SS400’s low carbon content makes it easy to weld. Most fabricators use arc welding or MIG welding to join pieces—no pre-heating is needed, which saves time. For example, a Korean construction company welded 500 tons of JIS SS400 for a bridge project in just 2 weeks.
- Machining: Drilling, cutting, and bending are simple with JIS SS400. Its ductility means it doesn’t crack during machining, even for complex shapes.
4. Standards and Specifications for JIS SS400 Structural Steel
JIS SS400 is governed by strict standards and specifications to ensure consistency. Here’s what you need to know:
- Primary Standard: JIS G 3101 (Japanese Industrial Standard for Carbon Structural Steels). This standard defines the alloy composition, mechanical strength, and testing requirements for JIS SS400.
- International Equivalents: JIS SS400 is similar to other global standards, including:
- ASTM A36 (U.S. standard)
- EN 10025 S235JR (European standard)
- GB/T 700 Q235 (Chinese standard)
- Quality Control & Conformance Testing: To be certified as JIS SS400, steel must pass:
- Tensile tests (to check tensile strength and yield strength)
- Bend tests (to test ductility)
- Chemical composition analysis (to verify carbon content and other elements)
- Material Certification: Reputable suppliers provide a mill certificate (like a MTC—Material Test Certificate) that proves the steel meets JIS G 3101 standards. Always ask for this before buying!
5. Comparison with Other Materials
How does JIS SS400 compare to other structural steels? Let’s look at key comparisons using a table:
| Material | Yield Strength (MPa) | Tensile Strength (MPa) | Key Advantage Over JIS SS400 | Key Disadvantage Over JIS SS400 |
| SS400 vs. A36 | 245 (SS400) / 250 (A36) | 400–510 (SS400) / 400–550 (A36) | A36 has slightly higher strength | SS400 is cheaper in Asia |
| SS400 vs. S235 | 245 (SS400) / 235 (S235) | 400–510 (SS400) / 360–510 (S235) | SS400 has higher yield strength | S235 is more common in Europe |
| SS400 vs. Q345 | 245 (SS400) / 345 (Q345) | 400–510 (SS400) / 470–630 (Q345) | Q345 is stronger (high-strength steel) | Q345 is 30% more expensive |
| SS400 vs. Stainless Steel (304) | 245 (SS400) / 205 (304) | 400–510 (SS400) / 515 (304) | 304 is corrosion-resistant | 304 costs 3x more than SS400 |
When to Choose JIS SS400 Over Others
- If you’re working on a budget (it’s cheaper than high-strength steel like Q345)
- If your project is in Asia (easy to source locally)
- If you need good weldability and ductility (better than some low-carbon steels like S235)
Yigu Technology’s View on JIS SS400 Structural Steel
At Yigu Technology, we’ve supplied JIS SS400 to over 500 construction and engineering clients in Asia. We believe JIS SS400 remains a top choice for mid-range structural projects because it balances performance, cost, and ease of use. For clients building warehouses, small bridges, or commercial buildings, it’s a reliable option that doesn’t require premium pricing. We also recommend pairing JIS SS400 with our anti-corrosion coatings for outdoor projects—this extends its lifespan by up to 15 years. As the demand for sustainable construction grows, we’re seeing more clients use recycled JIS SS400, which keeps projects eco-friendly without losing strength.
FAQ About JIS SS400 Structural Steel
- Can JIS SS400 be used in cold climates?
Yes, but it’s important to check its impact resistance at low temperatures. For projects in areas with temperatures below -20°C, we recommend choosing JIS SS400 with a “D” grade (tested for low-temperature toughness) to avoid brittleness.
- Is JIS SS400 suitable for welding with other steels?
Absolutely. Its low carbon content makes it compatible with other structural steels like ASTM A36 or EN S235. Just use a welding rod that matches the lower-strength material (e.g., E7018 for JIS SS400 and A36 joints) to ensure strong welds.
- How do I verify if the JIS SS400 I’m buying is genuine?
Ask the supplier for a Material Test Certificate (MTC) that includes: chemical composition data, mechanical test results, and a stamp from a JIS-accredited lab. You can also check the steel’s surface for a JIS G 3101 marking—genuine products will have this etched or printed on the surface.
