Size and Format
The 4 by 8 designation refers to the imperial sheet size of 4 feet by 8 feet, which converts to about 1219 mm by 2439 mm. The size is widely used in export trade because it suits container loading and standard cutting plans. Thickness ranges from about 1.5 mm to 25 mm for general supply. Hot rolled plate of this size is supplied with a mill finish, either pickled and oiled or with the normal mill scale. The cut edges may be sheared or flame cut, and the buyer should specify which edge condition is required because it affects the edge squareness and the presence of a heat affected zone.
Grades and Their Properties
SS400 under JIS G 3101 has a minimum yield strength of 245 MPa and a tensile range of 400 to 510 MPa, making it the general purpose grade for structural and fabrication work. ASTM A36 has a minimum yield strength of 250 MPa and a tensile range of 400 to 550 MPa and is the reference structural grade in North American practice. NM400 is a quenched abrasion resistant grade with a surface hardness of 370 to 430 HBW, used where the sheet forms a wearing surface rather than a structural member. Shipbuilding plate is produced to classification society rules in grades A, B, D and E, with the letter denoting the impact test temperature and the toughness level.
| Grade | Standard | Key Property | Main Use |
| SS400 | JIS G 3101 | 245 MPa minimum yield | General structure |
| A36 | ASTM A36/A36M | 250 MPa minimum yield | Structural plate |
| NM400 | GB/T 24186 | 370 to 430 HBW | Wear surface |
| Ship plate grades A to E | Classification society rules | Impact tested toughness | Hull and marine structure |
Choosing Between Structural, Wear and Ship Plate
Structural plate is chosen when the sheet carries load and must be welded into a frame. It has moderate strength, good ductility and predictable weldability. Wear plate is chosen when the surface is exposed to abrasion, and it is normally attached to a structural backing rather than carrying primary load. Ship plate is chosen when the classification society requires certified material with a defined impact energy. The grade letter indicates the test temperature, with grade A tested at zero degrees Celsius and grades D and E tested at minus 20 and minus 40 degrees Celsius respectively. Using a general structural plate in place of ship plate is not acceptable where the rules apply.
Fabrication and Handling
All these plates can be cut by shearing, plasma, laser or water jet, and they can be formed by rolling or pressing within the limits of their ductility. Wear plate has the least ductility and should be formed with generous radii. Surface protection during transport matters, particularly for pickled plate, which will rust quickly if it is not kept dry. Sheets are normally stacked on timber dunnage with protection at the edges to prevent mechanical damage.
Typical Applications
General fabrication and structural base plates.
Equipment frames and support brackets.
Chute and hopper wear liners in NM400.
Marine structures and hull internals in ship plate.
Storage tanks and ducting in SS400 and A36.
Frequently Asked Questions
Q: What does 4 by 8 mean for steel plate?
It is the imperial sheet size of 4 feet by 8 feet, which converts to about 1219 mm by 2439 mm and is a standard export and container friendly format.
Q: Can A36 and SS400 plate be used interchangeably?
They have similar strength and both are weldable, but the governing standard differs, so the specification should be fixed and the certificate checked against it.
Q: What is the difference between ship plate and ordinary plate?
Ship plate is certified by a classification society and carries a guaranteed impact energy at a defined temperature, while ordinary structural plate does not unless it is ordered with that requirement.
Q: Is NM400 plate suitable for structural use?
It is used as a wear facing rather than as a primary structural member because its ductility and weldability are lower than those of structural plate.
Q: How should the plates be stored?
Store them flat on timber dunnage, keep them dry and protect the edges, especially for pickled and oiled plate which rusts quickly when wet.