DX51D+Z275 steel sheet -
what the full designation means
DX51D+Z275 is the most widely purchased hot-dip galvanised sheet in Europe: a low-carbon steel for cold forming in grade DX51D with a zinc coating of at least 275 g/m² in total on both sides, around 20 µm per side. The full designation to EN 10346, however, contains three more elements, for example DX51D+Z275-N-A-C, which define the coating finish, the surface quality class and the surface treatment. Each of them affects how the sheet behaves in forming, painting and storage.
The designation element by element
| Element | Example | Meaning |
|---|---|---|
| DX | DX51D | steel for cold forming, X means that the rolling condition of the substrate (hot or cold) is not specified |
| 51 | DX51D | grade number, 51 stands for basic suitability for bending and roll forming |
| D | DX51D | steel intended for hot-dip coating |
| +Z | +Z275 | coating type: zinc (others include +ZA, +AZ, +ZM, +AS, +ZF) |
| 275 | +Z275 | minimum coating mass in g/m² in total on both sides, in the triple spot test |
| N or M | -N | coating finish: normal spangle (N) or minimised spangle (M) |
| A, B or C | -A | surface quality class |
| C, O, CO, P, S, U | -C | surface treatment, for example chemical passivation (C) or oiling (O) |
The DX51D grade itself has the material number 1.0226. More on the designation system for sheet, including cold-rolled and structural grades, can be found in the article on steel sheet grade designations.
DX grades and their properties
DX51D is the basic grade, without yield strength requirements. Subsequent grades have progressively lower strength and higher elongation, so they cope better with pressing.
| Grade | Re [MPa] | Rm [MPa] | A80 min [%] | Typical application |
|---|---|---|---|---|
| DX51D | not specified | 270-500 | 22 | bending, roll forming, ducts, enclosures |
| DX52D | 140-300 | 270-420 | 26 | shallow pressing |
| DX53D | 140-260 | 270-380 | 30 | medium pressing |
| DX54D | 120-220 | 260-350 | 36 | deep drawing |
| DX56D | 120-180 | 260-350 | 39 | extra deep drawing |
For load-bearing parts where a guaranteed yield strength matters, structural grades of the S series are used, for example S250GD or S350GD. Their applications are described in the article on galvanised steel in construction.
Coating mass and zinc thickness
The number in the coating designation is the zinc mass in grams per square metre, in total on both sides. With a zinc density of 7.14 g/cm³ it is easy to convert into thickness. For Z275, the minimum mass in a single measuring spot is 235 g/m².
| Coating | Minimum mass, both sides | Approximate thickness per side |
|---|---|---|
| Z100 | 100 g/m² | 7 µm |
| Z140 | 140 g/m² | 10 µm |
| Z200 | 200 g/m² | 14 µm |
| Z225 | 225 g/m² | 16 µm |
| Z275 | 275 g/m² | 20 µm |
| Z350 | 350 g/m² | 25 µm |
| Z450 | 450 g/m² | 32 µm |
| Z600 | 600 g/m² | 42 µm |
Z275 is the standard because it balances corrosion protection, formability and cost well. Outdoors in an urban environment, such a coating without painting typically provides, according to calculations based on EN ISO 9223, from around 10 to almost 30 years of protection. A comparison with electrolytic coatings can be found in the article on hot-dip and electro-galvanised steel.
Zinc spangle and surface quality class
Zinc spangle is the visible crystalline structure of the coating. Normal spangle (N) forms when zinc solidifies freely and is available only in surface quality class A. Minimised spangle (M) gives a fine, less visible structure and can be supplied in classes A, B and C.
Class A allows minor appearance imperfections and is sufficient for most technical applications. Class B is a surface improved by skin passing, and class C has a face side prepared for high-quality paint coatings. The higher the class, the more the appearance of the finished product matters.
Surface treatment
| Symbol | Treatment | When it is used |
|---|---|---|
| C | chemical passivation | most common, limits white rust formation during transport and storage |
| O | oiling | protection in storage and lubrication during pressing |
| CO | passivation and oiling | increased protection for longer storage |
| P | phosphating | better paint adhesion and formability |
| S | sealing | protection against soiling and fingerprints |
| U | untreated | only on explicit request, when the surface goes straight to further processing |
The type of treatment matters above all for painting and longer storage. Passivated sheet requires different preparation for paint than oiled sheet, as described in the article on painting galvanised steel sheet, and untreated sheet is quicker to develop white rust.
Applications of DX51D+Z275
DX51D+Z275 is the basic material for manufacturing ventilation ducts, cold-formed profiles, enclosures, machine and equipment components, gutters, flashings and hall equipment. It works wherever the part is bent or roll formed rather than deep drawn, and where good corrosion protection at a reasonable material cost matters.
Available steel grades, coating types and coil, strip and sheet formats are presented in the HEN-STOL steel sheet offer, with separate pages for galvanized steel sheet, cold-rolled steel sheet and hot-rolled steel sheet.
See how we can help
HEN-STOL supplies galvanised steel in grade DX51D and in higher DX and S GD grades, in coils, strip and sheets, from 5 tonnes. Send us the specification with thickness, width, coating and application, and we will check the available lots and advise on the most favourable option.
Frequently asked questions
What does DX51D mean?
DX51D is a low-carbon steel grade for cold forming to EN 10346, intended for hot-dip coating. The initial D stands for steel for cold forming, X for an unspecified rolling condition of the substrate, 51 is the grade number, and the final D indicates suitability for hot-dip coating. The material number is 1.0226.
What does Z275 mean on galvanised steel?
Z275 is a zinc coating with a mass of at least 275 g/m² in total on both sides of the sheet, measured in the triple spot test. This corresponds to around 20 µm of zinc on each side. In a single measuring spot the mass may not be lower than 235 g/m².
How many microns is a Z275 coating?
Around 20 µm on each side of the sheet. This follows from converting 275 g/m² over two sides at a zinc density of 7.14 g/cm³. The actual thickness may vary slightly from place to place, which is why the standard specifies coating mass rather than thickness.
What is the difference between DX51D and S250GD?
DX51D is a grade for cold forming, without a required yield strength, intended for bending and roll forming. S250GD is a structural grade with a guaranteed yield strength of at least 250 MPa, used in load-bearing parts, for example profiles and building structures.
What does the -N-A-C suffix in a sheet designation mean?
N stands for normal zinc spangle, A for surface quality class A, and C for chemical passivation. The full designation DX51D+Z275-N-A-C therefore describes hot-dip galvanised sheet with a 275 g/m² coating, a standard appearance and protection against white rust during transport and storage.
Is DX51D+Z275 sheet suitable for outdoor use?
Yes. In an urban environment a Z275 coating typically provides from around 10 to almost 30 years of protection without painting, and even longer in combination with paint (a duplex system). In highly corrosive industrial or coastal environments, a thicker coating or additional painting is worth considering.
Sources
- EN 10346, Continuously hot-dip coated steel flat products, 2015
- EN 10143, Continuously hot-dip coated steel sheet and strip - tolerances on dimensions and shape, 2006
- EN 10027-1, Designation systems for steels - steel names, 2016
- EN ISO 14713-1, Zinc coatings - guidelines and recommendations for the protection against corrosion, 2017