JIS SM490 Structural Steel: The Guide for Engineers and Constructors

If you’re involved in building high-strength structures like tall buildings or heavy-duty bridges, you need a material you can trust. JIS SM490 structural steel is a top pick for such projects—it offers exceptional strength while remaining easy to work with. In this guide, we’ll cover everything from its core properties to real-world uses, how it’s made, and how it compares to other steels. Our aim is to help you decide if it’s the right fit for your next project.

1. Material Properties of JIS SM490 Structural Steel

To use JIS SM490 effectively, you first need to understand its material properties. Let’s break down its composition and key mechanical traits.

Alloy Composition & Carbon Content

JIS SM490 is a low-alloy structural steel, designed for strength without sacrificing workability. Its alloy composition includes:

• Carbon Content: 0.18–0.23% (low enough for good weldability, but higher than mild steels like SS400)
• Manganese: 1.00–1.60% (boosts mechanical strength and toughness)
• Silicon: 0.15–0.35% (improves heat resistance during manufacturing)
• Phosphorus: Max 0.035% (kept low to prevent brittleness)
• Sulfur: Max 0.035% (reduces the risk of cracking during welding)
• Copper: 0.20% max (adds slight corrosion resistance)

Mechanical Strength & Key Metrics

What sets JIS SM490 apart is its impressive mechanical strength. Below is a table of its critical properties (tested at room temperature):

Other Important Properties

• Magnetic Properties: Like most structural steels, JIS SM490 is ferromagnetic. This makes it easy to test for cracks using magnetic particle inspection—a common quality check in construction.
• Toughness: Even at low temperatures (down to -10°C), it maintains good ductility, thanks to its alloy mix. This is crucial for outdoor structures in cooler climates.

2. Applications of JIS SM490 Structural Steel

JIS SM490’s high yield strength and tensile strength make it ideal for projects that need to handle heavy loads or harsh conditions. Let’s look at its most common applications with real examples.

Construction and Infrastructure

Most JIS SM490 is used in demanding construction and infrastructure projects:

• High-Rise Buildings: The steel’s strength allows for thinner columns and beams, freeing up space inside. For example, the 48-story Lotte City Hotel in Busan, South Korea, used JIS SM490 for its core structural framework—this reduced the building’s overall weight by 15% compared to using mild steel.
• Bridges and Beams: Long-span bridges rely on JIS SM490’s ability to handle heavy traffic and environmental stress. The Incheon Bridge (a 12.3km sea-crossing bridge in South Korea) used over 10,000 tons of JIS SM490 for its main support beams, ensuring it could withstand strong winds and ship impacts.
• Industrial Buildings: Factories with heavy machinery (like automobile plants) use JIS SM490 for columns and girders. A Toyota manufacturing facility in Nagoya, Japan, used this steel to support overhead cranes that lift 50-ton parts—its high strength prevents bending or sagging.

General Engineering Use

Beyond construction, JIS SM490 is used in:

• Heavy equipment frames (e.g., bulldozers and cranes)
• Pressure vessels (for storing industrial gases)
• Railway bridges and train car frames (thanks to its vibration resistance)

3. Manufacturing Processes for JIS SM490 Structural Steel

JIS SM490’s strength comes from careful manufacturing processes that balance performance and cost. Here’s how it’s made:

1. Hot Rolling: The primary process for JIS SM490. Steel billets are heated to 1,250°C (hotter than mild steels) and rolled into shapes like plates, beams, or bars. This process aligns the steel’s grain structure, boosting mechanical strength. Nippon Steel, a major producer, uses hot rolling for 90% of its JIS SM490 products.
2. Pickling: After rolling, the steel is dipped in hydrochloric acid to remove rust and scale. This step ensures a clean surface for welding or painting—critical for outdoor projects.
3. Annealing: Some JIS SM490 products undergo annealing (heating to 820°C and cooling slowly) to reduce internal stress. This is common for steel used in precision parts, like pressure vessel components.
4. Welding: While JIS SM490 has a slightly higher carbon content than mild steel, it’s still weldable. Fabricators use low-hydrogen welding rods (like E8018-B2) to prevent cracking. For example, a Chinese construction company welded 800 tons of JIS SM490 for a bridge project in 3 weeks—no pre-heating was needed for thin plates.
5. Heat Treatment: For extra strength, some JIS SM490 is quenched and tempered (heated, cooled quickly, then reheated). This process can raise its yield strength to over 400 MPa, but it’s only used for high-demand projects like offshore platforms.

4. Standards and Specifications for JIS SM490 Structural Steel

JIS SM490 is governed by strict standards and specifications to ensure consistency across suppliers. Here’s what you need to know:

• Primary Standard: JIS G 3106 (Japanese Industrial Standard for Weldable Structural Steels). This standard defines the alloy composition, mechanical strength (like minimum yield strength of 325 MPa), and testing requirements for JIS SM490.
• International Equivalents: JIS SM490 is similar to other global high-strength steels, including:
• ASTM A572 Grade 50 (U.S. standard)
• EN 10025 S355JR (European standard)
• GB/T 1591 Q345 (Chinese standard)
• Quality Control & Conformance Testing: To be certified as JIS SM490, steel must pass:
• Tensile tests (to verify tensile strength and yield strength)
• Charpy impact tests (to check toughness at low temperatures)
• Chemical analysis (to confirm carbon content and alloy levels)
• Material Certification: Reputable suppliers provide a Material Test Certificate (MTC) with every order. This document includes test results and a stamp from a JIS-accredited lab—always ask for it to ensure you’re getting genuine JIS SM490.

5. Comparison with Other Materials

How does JIS SM490 stack up against other structural steels? Below is a table comparing it to common alternatives:

When to Choose JIS SM490 Over Others

• If your project needs high strength (e.g., high-rises, long-span bridges)
• If you’re working in Asia (easy to source locally, reducing shipping costs)
• If you need a balance of strength and weldability (better than ultra-high-strength steels)

Yigu Technology’s View on JIS SM490 Structural Steel

At Yigu Technology, we’ve supplied JIS SM490 to over 300 infrastructure projects across Asia. We see it as a “workhorse” for high-demand builds—its strength lets clients design slimmer, more efficient structures, while its weldability keeps construction on track. We often recommend it for clients moving from mild steel (like SS400) to stronger materials, as it requires minimal changes to existing fabrication processes. For coastal projects, we pair it with our zinc-rich coatings to boost corrosion resistance, extending service life by up to 20 years. It’s a cost-effective choice for projects that can’t compromise on strength.

FAQ About JIS SM490 Structural Steel

1. Can JIS SM490 be used in cold climates?

Yes, but check its grade. JIS SM490 has grades like SM490A (for warm climates) and SM490B (tested for -10°C). For temperatures below -20°C, choose SM490C or SM490D—these are tempered for better low-temperature toughness.

2. Is JIS SM490 more expensive than SS400?

Yes, typically 15–20% more. But it’s worth it for projects needing higher strength—you’ll use less steel (since it’s stronger), which can offset the higher material cost. For example, a bridge using SM490 may need 20% fewer beams than one using SS400.

3. What’s the maximum thickness for JIS SM490 plates?

Most suppliers offer JIS SM490 plates up to 100mm thick. For thicker plates (100–200mm), you’ll need to order custom from mills like Nippon Steel or POSCO. Thicker plates may require pre-heating before welding to prevent cracking.