JIS SS400 Steel: A36 Equivalent, Properties & Applications
SS400 is Japan’s most widely used structural steel, ideal for bridges, buildings, and machine frames where cost efficiency matters more than high strength. It falls in the same strength class as ASTM A36 (USA) and EN S235JR/S275JR (Europe), offering excellent weldability at a low price point.
Equivalent Grades — SS400, A36, and International Standards
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G3101 | SS400 | Japan | — |
| ASTM A36/A36M | A36 | USA | Nearest Equivalent |
| ISO 630-2 | S275JR | International | Nearest Equivalent |
| DIN 17100 | St44-2 | Germany (legacy) | Nearest Equivalent |
| EN 10025-2 | S235JR / S275JR | Europe | Nearest Equivalent |
Chemical Composition — Side by Side
| Element | SS400 (JIS G3101) | A36 (ASTM A36M) |
|---|---|---|
| C (Carbon) | Not specified (≤0.25% typical) | ≤0.26% (t ≤ 19 mm) |
| Mn (Manganese) | Not specified | — |
| P (Phosphorus) | ≤0.050% | ≤0.040% |
| S (Sulfur) | ≤0.050% | ≤0.050% |
| Si (Silicon) | Not specified | — |
Sources: JIS G3101:2015, ASTM A36/A36M-19
Mechanical Properties Comparison
| Property | SS400 (t ≤ 16 mm) | A36 |
|---|---|---|
| Tensile Strength | 400–510 MPa (58–74 ksi) | 400–550 MPa (58–80 ksi) |
| Yield Point | ≥245 MPa (36 ksi) | ≥250 MPa (36 ksi) |
| Elongation | ≥21% | ≥20% |
| Hardness | ~120 HB (reference) | ~119 HB (reference) |
| Charpy Impact | Not specified | Not specified |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ (0.284 lb/in³) |
| Thermal Conductivity | ~51 W/m·K |
| Thermal Expansion | ~11.7 × 10⁻⁶ /°C |
| Young’s Modulus | 206 GPa (29,900 ksi) |
Heat Treatment Conditions
| Process | Temperature Range | Cooling |
|---|---|---|
| Annealing | 820–870°C (1508–1598°F) | Furnace cool |
| Normalizing | 870–920°C (1598–1688°F) | Air cool |
| Quenching | Not recommended | Low hardenability |
SS400 has low hardenability and is not suited for quench-and-temper processes. If heat-treated strength is required, consider S45C or SCM440 instead.
Practical Guide — Machinability, Welding, and Common Mistakes
Machinability
SS400 machines easily. It is softer than S45C (medium carbon steel), resulting in longer tool life and higher cutting speeds. A good choice for high-volume parts where machining cost matters.
Welding Tips
- Preheat: Not required for thickness ≤ 25 mm (0.98 in)
- Preheat (thick plate): 50–100°C (122–212°F) for t > 25 mm
- Recommended consumables: Low-hydrogen electrodes (e.g., JIS Z3212 D4316 / AWS E7016)
- Weldability is excellent — one of SS400’s strongest advantages
Common Mistakes
- “A36 = SS400” assumption: Close, but not identical. The yield strength specification method differs, and substitution without checking can cause issues in thin-plate designs.
- Using SS400 in low-temperature service: JIS G3101 does not require Charpy impact testing. Avoid SS400 below 0°C (32°F) — use SM400B, SM490B, or a dedicated low-temperature grade instead.
When to Choose SS400 — Selection Matrix
| Situation | Recommendation |
|---|---|
| Cost-sensitive structural parts | ✅ SS400 is ideal |
| Need higher strength | Consider SM490 (JIS G3106) |
| Low-temperature or impact loading | Use SM400B / SM490B |
| Heat treatment required | Use S45C or SCM440 |
| Demanding fatigue conditions | Consult a structural engineer |
Frequently Asked Questions
They are close but not identical. Both fall in the same strength class, but ASTM A36 explicitly requires a minimum yield strength of 250 MPa (36 ksi), while SS400’s yield point varies by thickness. For non-critical general fabrication, substitution is commonly accepted. For structural designs, always verify against the applicable standard.
JIS G3101 does not mandate Charpy impact testing for SS400, making it unsuitable for service below 0°C (32°F) without additional verification. For cold environments, select SM400B, SM490B, or a designated low-temperature structural steel.
Both are general structural steels under JIS G3101, but with different tensile strength ranges: SS400 is 400–510 MPa (58–74 ksi), while SS490 is 490–610 MPa (71–88 ksi). Choose SS490 or SM490 when higher strength is needed.
Yes. SS400 is one of the most weldable structural steels available. No preheat is needed for plates up to 25 mm (0.98 in) thick, and standard low-hydrogen electrodes work well.
“SS” stands for Steel Structure (鋼構造, kōkōzō) in Japanese industrial terminology. The number 400 refers to the minimum tensile strength in MPa.
Summary
- SS400 is Japan’s most widely used structural steel, with excellent weldability and low cost.
- SS400 and ASTM A36 are Nearest Equivalents — close in strength class, but not exact. The yield strength specification differs by thickness and standard.
- Chemical composition: SS400 is less tightly controlled than A36, but in practice, the difference is negligible for general fabrication.
- Mechanical properties: Both offer similar strength (~400 MPa tensile) and elongation, with SS400 yield decreasing for sections > 16 mm.
- Substitution is acceptable for non-critical general fabrication, but structural applications require standard verification.
- Preheat is not needed for plates ≤ 25 mm, making SS400 ideal for field welding and rapid repair cycles.
- Low-temperature service requires SM400B or SM490B — avoid SS400 below 0°C.
comment