Galvanized steel coil is ordered in three designations more often than any other: SGCC and SGCH under JIS G3302, and DX51D under EN 10346. Within those grades two formats dominate enquiries - very thin material in the 0.12-0.13 mm band, and coils slit to a 1000 mm width. Between them they cover light roofing, ducting, appliance panels, packaging and general light-gauge forming.
What the SGCC, SGCH and DX51D Designations Mean
JIS G3302 is the Japanese industrial standard for hot-dip zinc-coated steel sheet and strip. In its designation system the S stands for steel, the G for galvanized and the C for cold rolled, while the final letter marks the quality class: SGCC is commercial quality for general forming, and SGCH is drawing quality, rolled from a softer and more ductile base steel that withstands deeper forming without cracking.
DX51D belongs to EN 10346, the European standard for continuously hot-dip coated flat steel products. Its letters describe the product rather than the coating, because the coating is added separately as a suffix. D identifies flat steel intended for cold forming, X records that the rolling condition of the base steel is not specified, 51 is the grade sequence number, and the closing D completes the designation. The coating suffix is then chosen as +Z for zinc, +ZA for zinc-aluminium, +AZ for aluminium-zinc or +ZF for zinc-iron.
The North American equivalent family sits in ASTM A653/A653M, which covers hot-dip zinc-coated steel sheet with its own grade and coating notation.
How the Three Designations Compare
| Designation | Standard | Base steel | Formability | Typical use |
|---|---|---|---|---|
| SGCC | JIS G3302 | Cold-rolled commercial quality | Moderate | Roofing, ducting, general panels |
| SGCH | JIS G3302 | Cold-rolled drawing quality | High | Deep-drawn and severely formed parts |
| DX51D +Z / +AZ | EN 10346 | Low-carbon steel for cold forming | High | Bending and profiling, building and appliance panels |
| Zinc-coated sheet | ASTM A653/A653M | Commercial and forming grades | Moderate to high | General construction and manufactured goods |
SGCC and DX51D often appear in the same applications and are sometimes treated as directly interchangeable, but the two standards do not define identical mechanical or coating requirements. Any substitution should be confirmed against the drawing or the buyer's own specification rather than assumed from a similar name.
Thin Gauge and 1000 mm Width in Practice
Very light thicknesses are chosen where weight and material cost matter more than structural rigidity: cable trays, ventilation ducting, packaging, light roofing and small formed parts. A coil around 1000 mm wide fits the common slitting, profiling and roll-forming lines used by roof-sheet and duct manufacturers, so it can be fed directly into corrugating or cut-to-length equipment without an extra slitting pass.
Two factors decide whether a thin coil behaves well in production. The first is thickness tolerance. At 0.12-0.13 mm, a small absolute deviation is a large proportion of the section, and it reappears immediately as variation in the formed profile. Dimensional tolerances for continuously hot-dip coated sheet and strip are set out in EN 10143, and ordering to the tighter class of that standard gives more predictable forming than buying on commercial tolerance alone.
The second factor is coating mass. Zinc coating designations such as Z100, Z140 or Z275 state the total zinc mass applied to both sides in grams per square metre. A lighter coating is enough for dry indoor panels, while building exteriors, coastal sites and humid industrial interiors need a heavier coating to reach the intended service life.
Surface Finish, Oiling and Processing
Galvanized coil is normally supplied with a visible spangle or with a skin-passed finish. Skin-passing flattens the surface, improves paint adhesion and removes the spangle, which makes it the usual choice for pre-painted and colour-coated lines. Coils are delivered dry, oiled or passivation treated; oiling and passivation guard against white rust, the wet-storage stain that forms when moisture is trapped between coil wraps during sea transport.
State the complete designation and standard: SGCC, SGCH or DX51D, with the coating suffix where EN 10346 applies.
Give thickness and width together with the tolerance class, not only the nominal size.
Specify coating mass as a designation such as Z140 or Z275, or as grams per square metre on each side.
Confirm the surface finish, spangled or skin-passed, and any passivation or oiling requirement.
Confirm coil inner diameter, coil weight, slit width and edge condition.
Where the coil will be painted, ask for forming and adhesion trials before mass production.
Frequently Asked Questions
Q: What is the difference between SGCC and SGCH?
Both are JIS G3302 hot-dip zinc-coated cold-rolled grades. SGCC is commercial quality for general bending and profiling, while SGCH is drawing quality made from a more ductile base steel for deeper forming without cracking.
Q: What does DX51D mean?
DX51D is an EN 10346 designation for continuously hot-dip coated flat steel: D for flat steel for cold forming, X for an unspecified rolling condition, 51 as the grade sequence number, and a closing D to complete the grade. The coating type is added as a suffix such as +Z or +AZ.
Q: Is DX51D the same as SGCC?
They are the closest equivalents across EN 10346 and JIS G3302 and are used in the same applications, but each standard sets its own requirements, so a substitution should be checked against the specification.
Q: What does a coating designation such as Z275 mean?
It states the total mass of zinc applied to both surfaces. Z275 means 275 grams per square metre in total across both sides, which is a much heavier coating than a light indoor grade such as Z100.
Q: Why order 1000 mm wide coil instead of a wider one?
A 1000 mm width matches the common roll-forming, profiling and slitting lines used for roofing sheet and ducting, so no extra slitting pass is needed and offcut waste stays low.
Q: How should thin galvanized coil be stored?
Keep it dry and under cover, off the ground, with air circulating around the coil; oiled or passivated surfaces plus dry storage prevent white rust between the wraps.