S350GD, S420GD and DX51D+Z: coated steel grades to EN 10346 explained
What S350GD+Z275, S420GD+ZM310 and DX51D+Z mean: minimum yield and tensile strength of EN 10346 structural and forming grades, coating types and masses, and which grades we roll purlins from.
Updated October 16, 2026
Continuously hot-dip coated steel strip — the material of galvanized purlins, roof and wall sheeting and many cold-formed sections — is specified to EN 10346. Its grade names pack three facts into one code: the steel, its minimum strength and the coating. This guide explains how to read them and lists the minimum mechanical values.
How to read the grade name
- S350GD — S for structural steel, 350 for the minimum yield strength in MPa, GD for a flat product intended for hot-dip coating. The same pattern gives S250GD, S280GD, S420GD and so on.
- DX51D — D for a flat product for cold forming, X for an unspecified rolling condition, 51 for the grade and the final D for hot-dip coating. DX grades are chosen for forming, not for a guaranteed yield strength.
- +Z275, +AZ150, +ZM310 — the coating type and its mass: grams per square metre, total on both faces.
A full designation therefore reads like S350GD+Z275: structural strip with at least 350 MPa yield, coated with 275 g/m² of zinc.
Structural grades: minimum mechanical properties
| Grade | Material no. | Yield strength (MPa) | Tensile strength (MPa) | Elongation A80 (%) |
|---|---|---|---|---|
| S220GD | 1.0241 | ≥ 220 | ≥ 300 | ≥ 20 |
| S250GD | 1.0242 | ≥ 250 | ≥ 330 | ≥ 19 |
| S280GD | 1.0244 | ≥ 280 | ≥ 360 | ≥ 18 |
| S320GD | 1.0250 | ≥ 320 | ≥ 390 | ≥ 17 |
| S350GD | 1.0529 | ≥ 350 | ≥ 420 | ≥ 16 |
| S390GD | 1.0238 | ≥ 390 | ≥ 460 | ≥ 16 |
| S420GD | 1.0239 | ≥ 420 | ≥ 480 | ≥ 15 |
| S550GD | 1.0531 | ≥ 550 | ≥ 560 | — |
S450GD follows the same naming: its minimum yield strength is 450 MPa. For the full requirements of any grade, including chemical composition, refer to EN 10346 and the mill certificate.
Forming grades: DX51D and the deep-drawing grades
| Grade | Yield strength Rp0.2 (MPa) | Tensile strength (MPa) | Elongation A80 (% min.) |
|---|---|---|---|
| DX51D | — | 270–500 | 22 |
| DX52D | 140–300 | 270–420 | 26 |
| DX53D | 140–260 | 270–380 | 30 |
DX51D has no specified yield strength, so it suits flashings, ducting, cladding substrates and other formed parts rather than load-bearing members. Where a section carries load — a purlin, a rail, a stud — specify a structural S…GD grade.
Coating types
| Code | Coating | Example |
|---|---|---|
| Z | Zinc (hot-dip galvanized) | Z275 = 275 g/m² total |
| ZM | Zinc–aluminium–magnesium (e.g. Magnelis) | ZM310 = 310 g/m² total |
| AZ | Aluminium–zinc (e.g. Aluzinc) | AZ150 = 150 g/m² total |
| ZA | Zinc–aluminium | ZA255 = 255 g/m² total |
| ZF | Zinc–iron alloy (galvannealed) | ZF100 = 100 g/m² total |
Coating choice depends on the environment more than on the grade. Our purlin coatings guide compares zinc, Magnelis and Aluzinc for buildings.
Grades we roll purlins from
- Galvanized purlins in S350GD+Z275 and S420GD+Z275.
- Magnelis purlins in S350GD, S420GD and S450GD with ZM310 or ZM350 coating.
- Aluzinc purlins from aluminium–zinc coated strip; the grade is confirmed in the quotation.
- Galvanized steel sheet in DX51D+Z.
When ordering, give the profile and size with the full designation, for example Z 200×60×15×2, S350GD+Z275, and send it through the quote form.
Frequently asked questions
Is S350GD the same as S355?
No. S355 is a hot-rolled structural steel to EN 10025, used for beams, plates and hollow sections. S350GD is hot-dip coated strip to EN 10346, used for cold-formed purlins and sheeting. Their minimum yield strengths are close (355 and 350 MPa), but they are different products made to different standards.
What does Z275 mean?
Z is a zinc coating and 275 is its mass in grams per square metre, counted on both faces together. It is the usual coating for galvanized purlins.
Can DX51D be used for purlins?
DX51D has no specified minimum yield strength, so it is not suited to load-bearing sections that are designed on yield strength. Purlins are rolled from structural grades such as S350GD or S420GD.
What is the difference between S350GD and S420GD?
S420GD has a higher minimum yield strength (420 against 350 MPa), so the same section can carry more load or span further. Both are available with zinc or zinc–magnesium coatings.
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