JIS G3302 Galvanized Steel Sheet Grade Guide: SGCC to SGCE — Coating Weight, Grades, and Specifications

JIS G3302 is the Japanese Industrial Standard for hot-dip zinc-coated (galvanized) cold-rolled steel sheets and coils. The standard covers five formability grades — SGCC through SGCE — and a complete designation system for coating weight, spangle type, surface treatment, and post-coating treatment. Reading a JIS G3302 designation correctly means understanding five independent parameters that define the delivered product. This guide explains the complete grade and designation system, the coating weight Z-code interpretation, the galvannealed (-ZF) variant, and how JIS G3302 maps to ASTM A653 and EN 10346.

1. Standard Scope

JIS G3302:2019 covers continuously hot-dip zinc-coated steel sheets and coils produced from cold-rolled steel base. Scope parameters:

• Thickness: 0.25–3.2 mm (base steel before coating)
• Width: 600–1800 mm standard commercial range
• Zinc coating: Pure zinc (standard) or zinc-iron alloy (galvannealed, -ZF variant)
• Base steel: Cold-rolled carbon steel; properties equivalent to JIS G3141 grades

The standard does not cover: hot-dip galvanized structural sections (JIS G3444 etc.), batch galvanizing of fabricated parts (JIS H0401), or electrogalvanized sheet (JIS G3313).

2. Grade Structure (SGCC to SGCE)

SGCC accounts for the large majority of JIS G3302 production volume — roofing, HVAC, construction, and general fabricated galvanized parts are all SGCC. The SGCD grades are used where the zinc coating must survive a draw; the zinc coating itself constrains the practical draw depth (see Section 8). SGCE is an uncommon grade combining higher-strength base steel with drawing capability.

3. Coating Weight Z-Code System

JIS G3302 coating weights are designated by Z## where ## is the minimum total zinc coating mass in g/m² (both sides combined). Both a total minimum and a per-side minimum apply:

To convert between JIS Z-codes and ASTM G-codes: ASTM A653 G-codes are in oz/ft² (both sides). Conversion: 1 oz/ft² = 305 g/m². ASTM G30 = 30/305 oz×g/ft×m² = approximately 92 g/m² → close to Z10. G60 ≈ Z18. G90 ≈ Z27.

4. Surface Type: Spangle and Galvannealed (-ZF)

Galvannealed (-ZF) detail: After the steel exits the zinc bath, it passes through an induction heating section (~500–550°C) that drives iron diffusion from the steel into the zinc coating, producing a uniform Fe-Zn alloy (7–12% Fe, zeta + delta intermetallic phases). The result:

• No free zinc — the entire coating is Fe-Zn alloy, matte grey in appearance
• Excellent adhesion for zinc phosphate + cathodic electrocoat primer (standard automotive pre-treatment)
• Better spot weld electrode life than pure zinc (less electrode sticking)
• Slightly reduced formability vs regular SGCC: the harder Fe-Zn alloy can powder or flake at tight bends — minimum bend radius is approximately 1.5× that of equivalent SGCC
• Cut-edge protection: slightly reduced vs regular SGCC (no free zinc), but the Fe-Zn alloy still provides some galvanic activity

5. Passivation and Post-Treatment Codes

Since the EU ELV Directive (2000/53/EC) and RoHS Directive phased out hexavalent chromium, almost all SGCC for automotive and consumer electronics applications is supplied with NCR (non-chromate) or trivalent chromate passivation. Building and construction applications may still use standard passivation where the final product is not regulated by RoHS/ELV.

6. Full Designation Matrix

A complete JIS G3302 product designation combines: Grade + Coating Weight + Surface Type + Passivation + Post-Treatment:

7. ASTM A653 and EN 10346 Equivalents

EN 10346 uses the same g/m² total convention as JIS G3302, making conversion straightforward: Z180 in EN 10346 = Z18 in JIS G3302. ASTM A653 oz/ft² conversion: G×305 = g/m² (G60 × 305 = 18,300 g/m² → wait, 0.60 oz/ft² × 305 = 183 g/m² ✓).

8. Mechanical Properties

Note: The elongation values for galvanized grades (SGCC ≥ 32%) are slightly lower than the equivalent uncoated grades (SPCC ≥ 34%) — the galvanizing anneal achieves the same minimum but the specification accounts for the slightly different test procedure applied to coated material. The zinc coating itself does not significantly affect tensile or elongation properties.

9. FAQ

Q: What is the difference between SGCC-ZF and galvannealed? Are they the same?

Yes — galvannealed steel is the same as SGCC-ZF (or SGCD-ZF for drawing grades). “ZF” is the JIS G3302 designation suffix for the zinc-iron alloy coating produced by in-line annealing after hot-dip galvanizing. “Galvannealed” is the industry trade term used internationally. “GA steel” is a common shorthand. All refer to the same product: Fe 7–12% in the zinc coating, matte grey surface, excellent paintability and weldability.

Q: Can I use SGCC for food packaging machinery?

Only for non-contact structural components. Zinc is approved as a food-contact material at trace levels, but bulk zinc dissolution from unprotected SGCC surfaces in wet food environments exceeds acceptable levels. Food-contact parts of food processing equipment should use SUS304 or SUS316 stainless steel. SGCC can be used for the machine structure, guards, and non-contact frames.