SPCC and SGCC: Decoding the Grade Names
SPCC and SGCC are the two grade families most often quoted for light gauge steel sheet and coil in export markets, and they describe different points in the same processing chain. SPCC is a cold rolled carbon steel sheet for general commercial use, produced by cold reduction and annealing without any metallic coating. SGCC is the galvanized version of that same commercial quality material, produced by giving an SPCC type substrate a hot dip zinc coating.
The naming logic is straightforward. The first letter refers to steel, the second to the product form, and the following letters mark the commercial, drawing or deep drawing quality. Because the substrate chemistry is similar, SGCC inherits the forming behaviour of SPCC and adds a corrosion resistant surface, which is why the two names so often appear side by side on a purchase specification.
Where DX51D Fits in the Coated Sheet Family
DX51D is the European equivalent family in EN 10346 and is widely treated as the counterpart of SGCC. It is a bending and forming grade with low carbon cold rolled substrate, and the coating is written after the plus sign, so DX51D+Z means a zinc coating and DX51D+AZ means an aluminium-zinc coating. The grade carries no guaranteed minimum yield strength, which is exactly what allows it to accept aggressive roll forming and bending.
| Designation | System | Character | Main use |
|---|---|---|---|
| SPCC | Uncoated cold rolled sheet | General commercial quality | Painted parts, panels, general fabrication |
| SGCC | Hot dip zinc coated sheet | Commercial quality with zinc layer | Roofing, cladding, appliances |
| DX51D+Z | EN 10346 coated sheet | Bending and forming grade | Roll formed profiles and cladding |
| DX53D+Z | EN 10346 coated sheet | Higher formability than DX51D | Deeper drawn and complex shaped parts |
DX53D and Higher Formability Grades
The DX51D, DX52D, DX53D and DX54D series form a ladder of increasing formability for coated sheet. Where DX51D covers general bending and profiling, DX53D is chosen when parts need deeper drawing, tighter radii or more complex geometry without cracking, and DX54D goes further for the most demanding forming operations. Because these grades continue to be cited in older drawings alongside the current coated sheet standard, buyers should confirm which edition and which steel number a legacy reference points to before releasing an order, so that the delivered material matches the draw intended by the design.
The practical rule is to select the softest, most formable grade that the finished part needs and the surrounding process can tolerate, since higher formability generally comes with a slightly higher price and with handling care that softer strip demands.
Z200 Coating: What the Number Tells You
The Z designation states the total zinc coating mass applied to both surfaces in grams per square metre, so a Z200 galvanized coil carries about 200 g/m2 in total, roughly 100 g/m2 per face. That is a mid to heavy class: comfortably above the thin Z100 and Z120 grades used indoors, and below the maximum Z275 class reserved for coastal and long life roofing.
Z100 to Z120 - interior panels, dry service and painted components.
Z140 to Z180 - sheltered external parts and general cladding.
Z200 - roofing, gutters, purlins and general outdoor structures in moderate climates.
Z225 to Z275 - coastal, industrial and long service life roofing systems.
Z200 is therefore a common export specification because it balances coating cost against a service life measured in decades in rural and urban air. As with any coating class, the atmosphere decides the outcome: chloride in sea air and sulphur in industrial air consume zinc far faster, so a coastal project may justify Z275 or an additional paint system instead.
AZ150 and Aluminium-Zinc Coated Steel
DX51D with an AZ coating is a different product from the familiar galvanized sheet. The AZ designation marks a hot dip aluminium-zinc alloy coating whose bath composition is about 55 percent aluminium, 43.4 percent zinc and 1.6 percent silicon, commonly written AZ150 for a total coating mass of 150 g/m2. The aluminium-rich layer gives superior heat resistance and higher thermal reflectivity than a pure zinc coating, and the Si addition keeps the alloy layer controlled so the coating stays adherent during forming.
That combination suits applications where radiant heat and reflectivity matter as much as corrosion resistance, such as roofing in hot climates and components exposed to moderate service temperatures, while conventional zinc coatings remain the better answer where sacrificial protection of cut edges is the priority.
Frequently Asked Questions
Q: Is SGCC the same as DX51D+Z?
They are equivalent in practical use rather than identical in wording. SGCC comes from the Japanese coated sheet system and DX51D+Z from the European standard, and both describe a commercial quality zinc coated substrate for forming.
Q: What does Z200 mean on a galvanized coil?
Z200 is the total zinc coating mass on both surfaces, about 200 g/m2 in total and roughly 100 g/m2 per side, which places it in the mid to heavy coating range for outdoor use.
Q: Can SGCC and SPCC be used in the same assembly?
Yes, but the corrosion performance is very different. SGCC is chosen for exposed or wet locations, while SPCC usually relies on paint for protection and is best kept in dry, interior service.
Q: What is DX53D used for?
DX53D is a higher formability coated grade, chosen where a part must be drawn or bent more severely than general profiling allows, such as complex shaped cladding and formed housings.
Q: Is AZ150 galvanized steel?
It is coated steel, but not zinc only. AZ150 is an aluminium-zinc alloy coating of about 55 percent aluminium, 43.4 percent zinc and 1.6 percent silicon, giving better heat resistance and reflectivity than a pure zinc layer.
Q: How should the grade and coating be specified on an order?
State the standard, the grade, the coating type and mass, plus thickness and width tolerances. For example, a construction order might read DX51D+Z200 to EN 10346, 0.50 mm thick by 1250 mm wide, which removes ambiguity at inspection.