In the world of structural engineering and steel procurement, the JIS G 3106 standard is the benchmark for rolled steels intended for welded structures. Among the most widely used grades are SM400A, SM400B, and SM400C. While they share a similar base tensile strength, their performance in low-temperature environments and specific chemical compositions vary significantly.
As a leading global steel supplier, GNEE STEEL provides this comprehensive guide to help you choose the right grade for your project.
Introduction to SM400C / SM400B / SM400A
SM400 is a carbon steel plate for welded structures defined in JIS G 3106 (Japanese Industrial Standards). It belongs to the SM400 series and is classified into three grades: SM400C, SM400B, and SM400A.
- A: No impact test required
- B: Impact test performed at 20℃ (room temperature)
- C: Impact test performed at 0℃
The core difference among these quality grades lies in the gradually stricter requirements for low-temperature impact toughness, making them suitable for different service environments.
The SM400 series is divided into several grades according to toughness requirements, where the letter suffix indicates the impact test temperature and performance guarantee:
SM400A
No specified impact test temperature; minimum longitudinal impact energy is not guaranteed.Suitable for: Normal-temperature, static-load structural parts such as purlins and brackets in factory buildings (non-critical components).
SM400B
Impact test temperature: 20℃; minimum longitudinal impact energy ≥ 27J.Suitable for: General bridges, building load-bearing members, and applications in temperate climates.
SM400C
Impact test temperature: 0℃; minimum longitudinal impact energy ≥ 47J.Suitable for: Cold-region bridges, ships, pressure vessels, and other structures subject to dynamic loads and risk of low-temperature brittle fracture.
SM400C / SM400B / SM400A steel plates not only meet basic mechanical properties (tensile strength: 400–510MPa, yield strength ≥ 245MPa) but also feature progressively tighter controls on low-temperature toughness and weldability, ensuring resistance to brittle fracture in cold or dynamic-load environments.
Technical Standards and Delivery Conditions
All SM400 series plates supplied by GNEE STEEL comply with the JIS G 3106-2004 technical standard. To meet diverse engineering requirements, these plates can be delivered in various heat-treated states:
- Hot Rolled (AR)
- Normalizing (N)
- Quenching + Tempering (Q+T)
The Core Difference: Impact Toughness
The primary distinction between the A, B, and C suffixes lies in their Charpy V-Notch Impact Test requirements. This determines how the steel performs under stress in different temperature environments:
| Grade | Impact Test Temperature | Min. Impact Energy (Longitudinal) | Ideal Application |
| SM400A | No Requirement | Not Guaranteed | Ambient temperature, static loads (e.g., brackets, purlins). |
| SM400B | 20°C | ≥ 27J | Standard load-bearing structures in temperate climates (e.g., general buildings). |
| SM400C | 0°C | ≥ 47J | Critical structures in cold regions or high-dynamic load environments (e.g., bridges, ships, pressure vessels). |
Chemical Composition (Melt Analysis)
The chemical makeup is strictly controlled to ensure weldability and strength. Below is the composition for plates with thickness ≤ 100mm (SM400C) and up to 200mm (SM400A/B).
| Grade | Thickness (mm) | C (max) | Si (max) | Mn | P (max) | S (max) |
| SM400A | ≤ 50 / >50-200 | 0.23 / 0.25 | - | ≥ 2.5* | 0.035 | 0.035 |
| SM400B | ≤ 50 / >50-200 | 0.20 / 0.22 | 0.35 | 0.60 - 1.50 | 0.035 | 0.035 |
| SM400C | ≤ 100 | 0.18 | 0.35 | 0.60 - 1.50 | 0.035 | 0.035 |
*Note: Mn content for SM400A varies by thickness and specific manufacturer protocols to ensure tensile properties.
Mechanical Performance
The SM400 series provides a stable balance of yield strength and ductility.
- Tensile Strength: 400–510 MPa for all grades.
- Yield Strength: Starts at ≥ 245 MPa (for thickness ≤ 16mm) and gradually adjusts based on plate thickness.
- Elongation: Ranges from 18% to 24% depending on the specimen type and plate thickness.
| Grade | Yield point or yield strength, N/m㎡ | Tensile strength | |||||
| Thickness mm | Thickness mm | ||||||
| ≤16 | 16 | 40 | 75 | 100 | 100 | ≤100 | |
| SM400A | ≥245 | ≥235 | ≥215 | ≥215 | ≥205 | ≥195 | 400-510 |
| SM400B | ≥245 | ≥235 | ≥215 | ≥215 | ≥205 | - | 400-510 |
| SM400C | ≥245 | ≥235 | ≥215 | ≥215 | - | - | 400-510 |
Dimensions and Tolerances
GNEE STEEL ensures that all SM400A/B/C plates meet the dimensional and weight tolerances specified in JIS G 3192, JIS G 3193, and JIS G 3194. For standard orders, width and length tolerances comply with Class A deviations of JIS G 3193.
Why Choose GNEE STEEL?
GNEE STEEL is a premier provider of high-quality carbon and alloy steel plates. Beyond the JIS G 3106 SM400 series, we maintain an extensive inventory of specialized steel products to serve the global energy, construction, and manufacturing sectors:
- Pressure Vessel Plates (ASTM/ASME): SA516 Gr70, SA516 Gr60, SA387 series (Gr5, Gr11, Gr22, Gr91), P91, P92.
- Chinese Standard Vessel Plates: Q245R, Q345R, Q370R, 15CrMoR, 12Cr1MoVR.
- HIC Resistant & Hydrogen Service Steel: Q245R(R-HIC), Q345R(R-HIC), 15CrMoR(H).
- Low-Temperature Service Steel: 16MnDR, 09MnNiDR, 08Ni3DR.
- European Standard (EN10028): 16Mo3, P265GH, P355GH, P355NH.
- Wear-Resistant Steel: NM360, NM400, NM450, NM500, Mn13.
- High-Strength & Alloy Steel: Q460, Q690, Q960, 40Cr, 42CrMo, 10CrMoAL.
Contact GNEE STEEL today for a quote on SM400 series plates or any of our high-performance steel solutions. Our technical team is ready to assist you in selecting the perfect material for your specific engineering needs.
