SGCC and DX51D+Z are the two most widely quoted commercial galvanized grades, and buyers ask the same question about them constantly: are they the same material under two names? For straightforward bending, roll forming and general fabrication, the honest answer is usually yes. For anything where a drawing carries guaranteed mechanical values, a coating minimum or a tolerance class, the answer is that it depends - and the difference is worth knowing before you place the order rather than after.
Both are commercial-quality, continuously hot-dip zinc-coated steel intended for cold forming. Neither carries a guaranteed yield strength. That is the single most important thing they share, and it is also the thing most buyers get wrong about both of them.
What Each Designation Actually Says
SGCC comes from JIS G 3302. The letters read Steel, Galvanized, Commercial quality, on a Cold-rolled base. The standard covers commercial, drawing and structural qualities; SGCC is the commercial one and the cheapest.
DX51D+Z comes from EN 10346. D marks it as a flat product for cold forming, X means no guaranteed yield strength, 51 is simply a sequence number, D means hot-dip coated, and +Z means a zinc coating.
The Numbers Do Not Mean the Same Thing
|
Designation |
What the number refers to |
Example |
|
Nothing. It is a sequence number |
"51" is not a strength value |
|
|
S350GD |
Minimum yield strength, MPa |
350 MPa yield |
|
SGC440 |
Minimum tensile strength, MPa |
≈335 MPa yield, 440 MPa tensile |
|
ASTM A653 SS Grade 50 |
Minimum yield, ksi |
50 ksi ≈ 340 MPa yield |
The figures in JIS structural grades are tensile strengths; the figures in EN structural grades are yield strengths. A buyer who matches "440" against "350" because both are structural galvanized grades has compared a tensile value with a yield value and moved a hundred MPa without noticing.
What Is Guaranteed, and What Is Not
|
Property |
DX51D+Z (EN 10346) |
SGCC (JIS G 3302) |
|
Yield strength |
Not specified |
Not specified |
|
Tensile strength |
270–500 MPa |
Commonly shown, not guaranteed the same way |
|
Elongation |
A80 ≥ 22 % at t ≥ 0.70 mm |
Measured on a JIS No. 5 piece, 50 mm gauge |
|
Coating verification |
Three-spot average plus single-spot minimum |
Normally reported as a coil average |
The Coating Codes Do Not Line Up
|
JIS class |
g/m² both faces |
Nearest EN class |
g/m² |
Note |
|
Z06 |
60 |
- |
- |
No EN equivalent; EN starts at Z100 |
|
Z08 |
80 |
- |
- |
No EN equivalent |
|
Z12 |
120 |
Z100 or Z140 |
100 / 140 |
No exact match either way |
|
Z18 |
180 |
Z200 |
200 |
EN side is heavier |
|
Z22 |
220 |
Z225 |
225 |
Close enough for most purposes |
|
Z27 |
270 |
Z275 |
275 |
The pair buyers mean when they say "equivalent" |
|
Z35 |
350 |
Z350 |
350 |
Exact |
|
Z45 / Z60 |
450 / 600 |
Z450 / Z600 |
450 / 600 |
Exact |
Z27 against Z275 is the substitution everyone makes, and in practice it is fine. But JIS also offers classes below anything EN lists, and those have no European equivalent. If a drawing calls for Z08, there is no EN grade that answers it.
Thickness tolerance is the last gap. JIS G 3302 and EN 10143 use different tolerance tables. Two coils bought to each at the same nominal thickness can both be in tolerance and still not measure the same.
When Substitution Works
Simple bending, roll forming, profiling, ductwork, general fabrication - substitute freely once the coating mass is matched.
Deep drawing or severe profiling - neither grade is right. Go to DX52D through DX54D+Z, or JIS SGCD1 through SGCD3.
Any structural calculation using a yield value - neither grade is right. Use S250GD through S550GD+Z, or JIS SGC340 through SGC570, and match on yield, not on the number in the name.
A drawing that names elongation, a single-spot coating minimum or a tolerance standard - substitution needs checking against that specific clause, not against the grade name.
Frequently Asked Questions
1. Is SGCC the same as DX51D+Z?
Close enough for general forming, not identical. They are defined in different standards with different guaranteed values, different test piece geometry and different coating verification methods.
2. Can I substitute on a drawing written to EN 10346?
Only if the drawing's requirements are met clause by clause. Send us the callout and we will confirm rather than assume.
3. Which coating class should I quote?
Quote the mass in g/m² and the system you are buying to. "Z275" and "Z27" are 5 g/m² apart, and the difference matters when a minimum is being tested.