SM400A and SM400B are Japanese standard (JIS G3106) structural steels, differing mainly in their impact toughness requirements, with B having better low-temperature performance than A, achieved through stricter quality control, though their base strength (400MPa tensile) and general carbon content are similar, making SM400B better for applications needing guaranteed toughness at 20°C versus SM400A's general use.
Chemical Composition
|
SM400AChemical Composition |
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|
Grade |
The Element Max (%) |
|||||
|
C |
Si |
Mn |
P |
S |
Cu (min) |
|
|
SM400A |
0.23-0.25 |
- |
2.5*C min |
0.035 |
0.035 |
- |
|
SM400BChemical Composition |
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|
Grade |
The Element Max (%) |
|||||
|
C |
Si |
Mn |
P |
S |
Cu (min) |
|
|
SM400B |
0.20-0.22 |
0.35 |
0.6-1.50 |
0.035 |
0.035 |
- |
Mechanical Property
|
Grade |
SM400A Mechanical Property |
|||
|
Thickness |
Yield |
Tensile |
Elongation |
|
|
SM400A |
mm |
Min Mpa |
Mpa |
Min % |
|
t≦16 |
245 |
400-510 |
18 |
|
|
16<t≦160 |
205-235 |
400-510 |
24 |
|
|
Grade |
SM400BMechanical Property |
|||
|
Thickness |
Yield |
Tensile |
Elongation |
|
|
SM400B |
mm |
Min Mpa |
Mpa |
Min % |
|
t≦16 |
245 |
400-510 |
18 |
|
|
16<t≦90 |
215-235 |
400-510 |
24 |
|
Key Differences
Impact Test: SM400A typically has no specified impact test, while SM400B requires a Charpy V-notch impact test at 20°C, ensuring toughness at room temperature (around 27J), according to this Scribd document and Bebon Steel.
Carbon Content: SM400B generally has a slightly higher maximum carbon content (around 0.23%) than SM400A, contributing to its increased strength and weldability considerations, notes this article from Solucky Steel.
Yield Strength: Both have similar strength ranges, but SM400B often has a minimum yield strength of 245 MPa, while SM400A can be slightly lower (e.g., 235 MPa or 245 MPa depending on thickness).
