SGCC and DX51D are the two most common designations in the galvanized coil trade, and G60 and G90 are the coating classes most frequently written on export documents. This article explains what each designation means, how G60 and G90 relate to the European Z system, where DX51D and DX53D differ in formability, and what a 1250 mm width specification implies for supply, slitting and packaging.
SGCC (JIS G3302) and DX51D (EN 10346)
Both designations describe continuous hot-dip galvanized low-carbon steel for general forming and bending. The difference is the standard system and the guaranteed values. JIS G3302 defines SGCC without a guaranteed yield strength: the usual guarantee is tensile strength of at least 270 MPa, with minimum elongation that depends on thickness. EN 10346 defines DX51D with a full mechanical envelope.
| Property | SGCC (JIS G3302) | DX51D (EN 10346) |
|---|---|---|
| Yield strength Rp0.2 | Not guaranteed | 140-300 MPa |
| Tensile strength Rm | ≥ 270 MPa | 270-500 MPa |
| Elongation A80 | Thickness-dependent | ≥ 22% (0.35-3.0 mm) |
For contracts written to European, Middle East or African standards, DX51D is the usual equivalent when SGCC is requested, and mills commonly certify one coil against both designations.
G60 and G90 coating classes (ASTM A653)
In ASTM A653 the letter G designates a zinc coating, and the number is the coating weight in ounces per square foot measured as the total on both surfaces. G60 means 0.60 oz/ft2, which is about 183 g/m2; G90 means 0.90 oz/ft2, about 275 g/m2. EN 10346 expresses the same weights with the Z series: Z180 and Z275 respectively. Coating mass drives corrosion life, so the choice between G60 and G90 is a durability decision for the application environment.
| Class | oz/ft2 total | g/m2 total | EN equivalent | Typical use |
|---|---|---|---|---|
| G40 | 0.40 | 122 | Z120 | Indoor profiles, ducting |
| G60 | 0.60 | 183 | Z180 | General construction |
| G90 | 0.90 | 275 | Z275 | Roofing, coastal exposure |
Formability: DX51D vs DX53D
DX51D is a bending and roll-forming grade: it handles corrugated profiles, simple folds and light stamping with an elongation of at least 22%. DX53D in EN 10346 is optimized for deep drawing: yield strength 140-260 MPa, tensile 270-380 MPa and elongation A80 of at least 26%. The extra ductility matters when a profile is drawn, embossed or severely stretched rather than simply bent. If a part cracks during deep drawing with DX51D, the first upgrade is DX53D, not a heavier coating.
1250 mm width and practical supply
1250 mm is a standard mill width for galvanized coil in both the JIS and EN product ranges, and it is the base width from which narrower slit coils are produced. The practical implications are straightforward: thickness is available from about 0.15 mm to 3.0 mm under EN 10346 and up to 6.0 mm under JIS G3302; width tolerance follows EN 10143 or the JIS tolerance table; inner diameter is normally 508 mm or 610 mm; and each coil is limited by the mill and transport weight, typically 3 to 15 tonnes depending on gauge. When a project needs many widths, ordering one 1250 mm master coil and slitting locally usually costs less than ordering several narrow coils.
Inspection and certification
For export shipments the certificate should state the standard, the grade, the coating class with the triple-spot value, the spangle type, the surface treatment (passivation, oiling or none) and the thickness measured at the agreed points. Cut-edge appearance, coil set and telescoping limits should be agreed in advance. Packaging for sea freight follows GB/T 247 for steel strip products, with VCI paper, edge protection and lashing points for the container.
Frequently Asked Questions
Is SGCC the same as DX51D? They are the same product family under different standards. SGCC is specified to JIS G3302, DX51D to EN 10346. Strength levels are comparable, but DX51D guarantees yield and elongation, while SGCC guarantees tensile strength only.
G60 or G90 for roofing? For sheltered inland roofs G60 can be sufficient, but for exposed or coastal roofs G90 (275 g/m2) is the safer choice because the heavier coating gives longer protection against salt and rain.
What does Z275 mean? Z275 means a zinc coating mass of 275 g/m2 total for both surfaces under EN 10346, which is the same coating as G90 in ASTM A653.
DX51D or DX53D for deep-drawn parts? Choose DX53D. Its elongation of at least 26% and lower yield strength allow deeper drawing without cracking; DX51D is limited to bending and light forming.
What does the G in G90 stand for? G stands for galvanized coating in the ASTM A653 designation system, and the number is the coating weight in ounces per square foot measured on both surfaces combined.
What widths can be produced from a 1250 mm coil? 1250 mm master coil can be slit into any combination of narrower widths down to about 20 mm, subject to the slitter capability, edge trim allowance and minimum strip width rules.