SS490 (JIS G3101) and ASTM A572 Gr.60 share overlapping tensile strength ranges but differ by 90 MPa (13 ksi) in design yield strength — a gap large enough to cause a critical structural error if the grades are treated as interchangeable. This guide covers equivalent grades, composition, mechanical properties, and when SS490 is and is not the right specification.
- International Equivalent Grades
- Chemical Composition
- Mechanical Properties
- Physical Properties
- Heat Treatment Conditions
- Machinability
- Weldability
- Common Mistakes
- When to Choose SS490
- FAQ
1. International Equivalent Grades
| Standard | Grade | Region | Match Type |
|---|---|---|---|
| JIS G3101 | SS490 | Japan | Reference |
| ASTM A572/A572M | A572 Gr.60 | USA | ✅ Nearest Exact (tensile range; yield differs significantly — see below) |
| EN 10025-2 | S355JR / 1.0045 | Europe | ⚠️ Nearest Equivalent (slightly higher yield) |
| ISO 630-2 | S355JR | International | ⚠️ Nearest Equivalent |
SS490 yield point (≥ 325 MPa / 47 ksi) is 90 MPa (13 ksi) lower than A572 Gr.60 (≥ 415 MPa / 60 ksi). These grades share a tensile strength range but are NOT equivalent in design yield. Substituting SS490 for A572 Gr.60 in yield-governed design is a critical engineering error.
2. Chemical Composition
JIS G3101 does not specify chemical composition for SS490 — only mechanical properties are guaranteed. Typical mill chemistry based on industry practice is shown below.
| Element | SS490 (typical mill) | ASTM A572 Gr.60 | EN S355JR |
|---|---|---|---|
| C | ≤ 0.18% (typical) | ≤ 0.23–0.26% | ≤ 0.22% |
| Mn | ≤ 1.50% (typical) | ≤ 1.35–1.60% | ≤ 1.60% |
| Si | — (not specified) | ≤ 0.40% | ≤ 0.55% |
| P | ≤ 0.050% | ≤ 0.040% | ≤ 0.040% |
| S | ≤ 0.050% | ≤ 0.050% | ≤ 0.045% |
Sources: JIS G3101:2020, ASTM A572/A572M, EN 10025-2
Because JIS G3101 does not control SS490 composition, carbon equivalent (Ceq) varies by mill and heat. For welded structures where composition control is required, specify SM490 (JIS G3106) instead.
3. Mechanical Properties
| Property | SS490 | ASTM A572 Gr.60 | EN S355JR |
|---|---|---|---|
| Tensile Strength | 490–610 MPa (71–88 ksi) | ≥ 520 MPa (≥ 75 ksi) | 470–630 MPa (68–91 ksi) |
| Yield Point (t ≤ 16 mm) | ≥ 325 MPa (≥ 47 ksi) | ≥ 415 MPa (≥ 60 ksi) | ≥ 355 MPa (≥ 51.5 ksi) |
| Elongation | ≥ 19% | ≥ 16% | ≥ 22% |
| Charpy Impact | Not required | Not required | ≥ 27 J at 20°C |
By yield strength, SS490 (325 MPa) is closer to ASTM A572 Gr.42 (290 MPa / 42 ksi) or A572 Gr.50 (345 MPa / 50 ksi) than it is to Gr.60. The “490” in SS490 refers to the minimum tensile strength in MPa, not the yield.
4. Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ (0.284 lb/in³) |
| Young’s Modulus | 200 GPa (29,000 ksi) |
| Thermal Conductivity | 50 W/(m·K) (347 BTU·in/(hr·ft²·°F)) |
| Thermal Expansion (20–100°C) | 11.7 × 10⁻⁶ /°C (6.5 × 10⁻⁶ /°F) |
| Specific Heat (approx.) | ~490 J/(kg·K) (0.117 BTU/(lb·°F)) |
5. Heat Treatment Conditions
| Process | Temperature | Cooling | Purpose |
|---|---|---|---|
| As-rolled | Rolling finish ~900°C (1,652°F) | Air cool | Standard supply condition |
| Stress Relief | 550–650°C (1,022–1,202°F) | Furnace cool | Post-fabrication residual stress reduction (when required) |
SS490 is supplied in the as-rolled condition. No strength heat treatment is applicable. Normalizing may be specified to improve toughness uniformity in plate products.
6. Machinability
- Machinability rating: approximately 65–70% relative to AISI 1212 baseline
- Standard HSS or carbide tooling suitable
- Slightly higher strength than SS400 may require marginally reduced cutting speeds
- Drilling, turning, milling, and flame/plasma cutting all performed with standard structural steel parameters
- No special tooling or coolant requirements compared to general structural mild steel
7. Weldability
- Weldability: Good for typical sections — no preheat required for t ≤ 25 mm (1 in) in ambient conditions
- Carbon equivalent varies by mill heat (composition not specified by JIS G3101); verify Ceq on mill certificate before welding thick sections
- For t > 25 mm (1 in) or restrained joints, preheat to 50°C (122°F) minimum as a precaution
- Recommended processes: SMAW (E7016/E7018), GMAW, FCAW — standard structural welding consumables
- For welded structures where composition control is critical, substitute SM490 (JIS G3106) which guarantees C limit and optional Charpy
- No Charpy impact requirement under JIS G3101 — do not use SS490 where toughness is a design requirement
8. Common Mistakes
SS490 yield point (≥ 325 MPa / 47 ksi) is 90 MPa (13 ksi) below A572 Gr.60 (≥ 415 MPa / 60 ksi). This is a 22% shortfall in design yield. Engineers who see both grades listed at “490–520 MPa tensile” and assume equivalence are comparing tensile floors — not yield points. For yield-governed design (beam sections, column stability), this substitution under-delivers on structural capacity. If a 60 ksi yield material is required, specify SM490Y (JIS G3106) or obtain SM490 material certified to the higher yield tier.
JIS G3101 SS490 has no Charpy impact requirement in the standard. For applications at 0°C (32°F) or below — cold storage structures, outdoor equipment in cold climates, or any impact-loaded connection — SS490 cannot guarantee the material will not undergo brittle fracture. Specify SM490B or SM490C (JIS G3106) for impact-tested structural plate, or SN490B for seismic applications with Charpy guarantee.
9. When to Choose SS490
✅ Choose SS490 when:
- ✅ General non-welded structural use in Japan where JIS G3101 is the procurement standard
- ✅ Non-critical applications where 490 MPa minimum tensile is the sole design driver
- ✅ Cost-sensitive applications where controlled composition is not required
- ✅ Mechanical parts, brackets, or frames where SS490 tensile range is adequate and welding is not involved
❌ Do not choose SS490 when:
- ❌ Welded structures requiring guaranteed composition control — specify SM490 (JIS G3106)
- ❌ Seismic applications — specify SN490B or SN490C (JIS G3136)
- ❌ Design against 60 ksi (415 MPa) yield — SS490 yield is only 325 MPa; use SM490Y or verify actual yield on certificate
- ❌ Low-temperature or impact-loaded applications — SS490 has no Charpy requirement; use SM490B/C
10. FAQ
Q: Why is SS490 yield lower than A572 Gr.60 despite similar tensile strength?
SS490 is a general structural grade (JIS G3101) with only a tensile floor and range specified. The standard does not control chemical composition, so the yield-to-tensile ratio varies by heat. A572 Gr.60 is an HSLA grade with explicit minimum yield point control (415 MPa / 60 ksi). The overlapping tensile range is coincidental — the design yield points differ by 90 MPa (13 ksi). When specifying structural steel, always compare yield points, not tensile designations.
Q: What is the closest ASTM equivalent for SS490 by yield strength?
By yield strength (≥ 325 MPa / 47 ksi), the closest ASTM grades are A572 Gr.42 (Fy = 290 MPa / 42 ksi) or A572 Gr.50 (Fy = 345 MPa / 50 ksi). By tensile strength range (490–610 MPa), A572 Gr.50 (Fu ≥ 450 MPa / 65 ksi min) partially overlaps. There is no ASTM grade that exactly matches SS490’s combination of tensile range and yield, because SS490 does not control composition — making an exact compositional equivalent impossible to define.
Q: Is SS490 suitable for low-temperature applications?
JIS G3101 SS490 has no Charpy impact requirement. For applications at 0°C (32°F) or below, or for any impact-loaded structural element, SS490 cannot guarantee adequate toughness. Specify SM490B (≥ 27 J at 0°C) or SM490C (≥ 47 J at 0°C) for low-temperature service. For seismic applications with Charpy requirements, use SN490B (≥ 47 J at 0°C).
Q: Can SS490 be used interchangeably with SM490?
No. SM490 (JIS G3106) specifies composition limits (C ≤ 0.20% for SM490B), Charpy impact testing options, and weld-qualified sub-grades. SS490 (JIS G3101) specifies only tensile properties with no composition control. While both can come from the same steel mill heat at similar strength levels, SM490 provides documented traceability that welded structural codes require. In any welded structural context, SM490 is the correct specification.
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