Steel SM400A
JIS SM400A · ASTM A36
SM400A is a Japanese carbon structural steel qualified specifically for welded construction, with a low carbon equivalent and properties close to ASTM A36.
Reference datasheet — SM400A is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the HR condition
SM400A tempers and conditions
SM400A is supplied in 5 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Stress relieved | Post-weld or post-machining stress relief (550–650 °C) for dimensionally critical or heavily welded weldments. | 260 | 425 | 30 | 115 HB | 11 % IACS |
HRDefault Hot rolled | Standard mill supply condition for plate, sections and flats — pick for general welded structures, buildings and bridge secondary members. | 275 | 440 | 26 | 125 HB | — |
Normalized | Choose for thick plate or when uniform fine-grain structure and better notch toughness / dimensional stability after cutting are needed. | 285 | 445 | 29 | 125 HB | 10.8 % IACS |
Cold rolled | Mill-controlled finishing temperature for finer grain without a separate heat treatment — used for medium-thickness bridge and ship plate. | 295 | 450 | 28 | 130 HB | 10.8 % IACS |
Thermomechanically controlled processed | Pick for heavy plate where low carbon equivalent (easier field welding, less preheat) plus good toughness is required. | 305 | 460 | 28 | 135 HB | 10.8 % IACS |
What is SM400A?
SM400A is a Japanese carbon structural steel qualified specifically for welded construction, with a low carbon equivalent and properties close to ASTM A36. It is chosen where fabrication is weld-intensive: 275 MPa yield, 440 MPa tensile, 26 % elongation and about 125 HB (70 HRB) hot-rolled, available hot-rolled, normalized, cold-rolled, TMCP or stress-relieved in plate and sheet. Strength is the trade-off — step up to SM490A or SM520 for higher loads. The steel has no inherent corrosion resistance and needs a full paint or galvanize system. SM400A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). SM400A has a yield strength of 275 MPa (39.9 ksi) and a tensile strength of 440 MPa (63.8 ksi) — weaker than 91% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi).
What is SM400A used for?
- bridges
- buildings
- shipbuilding
- welded structures
Advantages
- Readily welded — 95/100, better than 97% of steel grades
- High electrical conductivity — 10.8 % IACS, better than 94% of steel grades
- Easy to machine — 65/100, better than 93% of steel grades
- Forms and bends easily — 80/100, better than 93% of steel grades
- Conducts heat well — 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades
Limitations
- Low strength — 275 MPa (39.9 ksi), worse than 91% of steel grades
- Hard to polish — 45/100, worse than 84% of steel grades
SM400A properties
Typical room-temperature values for SM400A-HR; bars are the position among steel grades.
Physical3
SM400A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
SM400A has a yield strength of 275 MPa (39.9 ksi) and a tensile strength of 440 MPa (63.8 ksi) — weaker than 91% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SM400A is rated for continuous service to 350°C (662 °F). It conducts heat at 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SM400A conducts electricity at 10.8 % IACS, better than 94% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of SM400A takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
SM400A's machinability is good (65/100, better than 93% of steel grades); weldability excellent (95/100); formability very good (80/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SM400A is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SM400A
Is SM400A easy to machine?
Machines easily but gummy — use positive-rake tools, moderate speeds and good coolant; expect built-up edge and stringy chips typical of low-carbon steel.
Can SM400A be welded?
Excellent weldability by SMAW/GMAW/SAW with E70-class consumables; low carbon equivalent means no preheat below ~25 mm thickness in normal conditions.
Can SM400A be formed, bent or molded?
Good cold bending and press-brake behaviour (r ≈ 1.5–2 t); hot forming 900–1150 °C, normalize afterwards for thick sections.
SM400A chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C≤0.23 % for t ≤ 50 mm; ≤0.25 % for t > 50 mm (JIS G 3106) | ≤ 0.23 | 0.17 |
| MnMin 2.5 × C (no upper limit specified for SM400A) | ≈ 0.6 | 0.6 |
| SiNot specified for SM400A; typical mill practice | ≈ 0.2 | 0.2 |
| P | ≤ 0.04 | 0.02 |
| S | ≤ 0.04 | 0.01 |
| Fe | balance |
What surface finishes work on SM400A?
No anodizing; blast to Sa 2½ then epoxy/zinc-rich primer, hot-dip galvanize or metallize — bare surfaces rust within days outdoors.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SM400A in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- A36
How much does SM400A cost?
SM400A is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SM400A — frequently asked
What is SM400A used for?
SM400A is typically used for bridges, buildings, shipbuilding and welded structures. In short: weld-qualified A36 equivalent; highest weldability in family; low strength, high ductility.
What is the yield strength of SM400A?
SM400A has a typical yield strength of 275 MPa (39.9 ksi) and a tensile strength of 440 MPa (63.8 ksi) — weaker than 91% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is SM400A easy to machine?
Reasonably — machinability is rated good (65/100, better than 93% of steel grades). Machines easily but gummy — use positive-rake tools, moderate speeds and good coolant; expect built-up edge and stringy chips typical of low-carbon steel.
Can SM400A be welded?
Yes — weldability is rated excellent (95/100). Excellent weldability by SMAW/GMAW/SAW with E70-class consumables; low carbon equivalent means no preheat below ~25 mm thickness in normal conditions.
What surface finishes work on SM400A?
No anodizing; blast to Sa 2½ then epoxy/zinc-rich primer, hot-dip galvanize or metallize — bare surfaces rust within days outdoors.
Can SM400A be formed, bent or molded?
Good cold bending and press-brake behaviour (r ≈ 1.5–2 t); hot forming 900–1150 °C, normalize afterwards for thick sections.
What is the maximum service temperature of SM400A?
SM400A is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SM400A-HR and SM400A TMCP?
HR is the default condition — standard mill supply condition for plate, sections and flats — pick for general welded structures, buildings and bridge secondary members. TMCP: pick for heavy plate where low carbon equivalent (easier field welding, less preheat) plus good toughness is required. Yield strength is 275 MPa in HR versus 305 MPa in TMCP.
How much does SM400A cost?
SM400A is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- JIS G 3106 — Rolled steels for welded structure — Japanese Standards Association (2020)
- ASTM A36/A36M — Carbon Structural Steel — ASTM International (2019)
- GB/T 700 — Carbon structural steels (Q235) — SAC (2006)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- worldsteel LCI data for steel products — World Steel Association (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.