Where S355J0WP Sits in EN 10025-5
EN 10025-5 is the part of the European structural steel series that covers hot-rolled products with improved atmospheric corrosion resistance. Its grades carry the letter W: S355J0W, S355J2W and the phosphorus-bearing variant S355J0WP, which adds a final P to the designation. In the symbol, 355 is the minimum yield strength in MPa, J0 indicates impact testing at 0 degrees Celsius, W marks the weathering characteristic and P shows that the grade relies on phosphorus as part of its corrosion resistance.
The strength class is the same as the plain S355 grades, so a designer can substitute a weathering grade for an ordinary structural steel without changing the section size, provided the fabrication implications of the alloying are understood.
Chemical Composition: the Phosphorus Bearing Variant
The composition of S355J0WP differs from S355J0W in four important ways: carbon and manganese are lower, silicon is higher, and phosphorus is deliberately present in the range of 0.06 to 0.15 percent rather than being restricted to a maximum of 0.035 percent.
| Element, percent | S355J0WP |
|---|---|
| Carbon, max | 0.12 |
| Silicon, max | 0.75 |
| Manganese, max | 1.00 |
| Phosphorus | 0.06 to 0.15 |
| Sulphur, max | 0.035 |
| Nitrogen, max | 0.009 |
| Chromium | 0.30 to 1.25 |
| Copper | 0.25 to 0.55 |
Mechanical Properties
| Nominal thickness, mm | Minimum yield strength, MPa | Tensile strength, MPa |
|---|---|---|
| Up to 16 | 355 | 510 to 680 up to 3 mm, 470 to 630 above 3 mm |
| Above 16 up to 40 | 345 | 470 to 630 |
| Above 40 up to 63 | 335 | 470 to 630 |
| Above 100 up to 150 | Not normally tabulated for this grade | 450 to 600 |
Minimum elongation is 20 percent at the lower thicknesses, and the impact requirement is a minimum Charpy V-notch energy of 27 J at 0 degrees Celsius. The yield strength table for S355J0WP is normally published up to 63 mm, which reflects the thickness range in which the grade is supplied in practice; projects needing heavier weathering plate generally move to S355J0W or S355J2W, whose yield values extend to 150 mm.
Why Phosphorus, and What It Costs
Phosphorus is an economical way to raise atmospheric corrosion resistance. It concentrates in the developing oxide layer and helps produce a compact patina, and it also raises strength through solid solution strengthening, which is why the carbon and manganese contents can be reduced. The trade-off is metallurgical: phosphorus raises the ductile to brittle transition temperature, increases the risk of segregation and cracking during welding, and reduces toughness in the heat-affected zone. The grade is therefore intended for structures where welding is light or where connections are bolted or riveted, and it is not the right choice for thick, highly restrained welds or for service at low temperature.
Applications and Selection Limits
S355J0WP is widely used for architectural facades and cladding, exposed wall panels, freight wagon components, containers, exhaust and ventilation components, and light outdoor structures where a self-protecting, unpainted surface is wanted. It is a good choice for bolted and riveted assemblies and for thin sections that will be formed rather than heavily welded. It should not be used for permanent immersion, for buried service, for chloride-rich environments such as coastal splash zones, or where the surface will remain wet for long periods, because in those conditions the protective layer does not stabilise and the steel corrodes. Where low-temperature toughness is required, a J2 grade is the correct choice.
Ordering, Tolerances and Documentation
Plate is ordered with the grade, thickness, width, length, delivery condition and surface requirements stated explicitly. Dimensional tolerances for hot-rolled plate follow EN 10029, and where internal soundness matters, ultrasonic examination to EN 10160 can be specified. Delivery condition is normally as-rolled, with normalised supply available on request. The inspection certificate to EN 10204 3.1 records the chemical analysis including the phosphorus and copper contents, the tensile and elongation results and the impact values at 0 degrees Celsius.
Frequently Asked Questions
Q: What does the P in S355J0WP mean?
A: It identifies the phosphorus-bearing weathering grade, in which phosphorus is deliberately present at 0.06 to 0.15 percent to improve atmospheric corrosion resistance.
Q: Is S355J0WP the same as S355J0W?
A: No. They share a strength class but have different compositions. S355J0WP has higher phosphorus and silicon with lower carbon and manganese, and it is restricted in welding and low-temperature use.
Q: Can S355J0WP be welded?
A: It can be welded, but the phosphorus content limits the thickness and restraint for which welding is advisable. Bolted and riveted joints are preferred for exposed structures.
Q: What is the corrosion rate in normal atmospheres?
A: Once the protective layer stabilises, the corrosion rate falls far below that of structural carbon steel, which is why the grade is often left unpainted in normal atmospheric exposure.
Q: Why is the yield strength table limited to 63 mm?
A: Because the phosphorus-bearing grade is supplied mainly in thinner plate. Heavier weathering plate is normally ordered as S355J0W or S355J2W.
Q: What surface and tolerance standards apply?
A: Plate dimensions and tolerances follow EN 10029, ultrasonic examination can be ordered to EN 10160, and the material is certified to EN 10204 3.1.
