JIS G3302 Galvanized Steel Coil Explained: SGCC Grades, Z Coatings & Procurement Guide

“Hot-dip zinc-coated steel sheet and strip”

JIS G3302 (Japan) — Common Coil Classes & Procurement

Engineering & Ordering Guide for Roll Forming Applications

JIS G3302 is the primary Japanese Industrial Standard covering:

“Hot-dip zinc-coated steel sheet and strip”

It governs:

Base steel grade
Coating mass (Z classes)
Mechanical properties
Surface finish
Testing and inspection

For roll forming manufacturers sourcing coil from:

Japan
South Korea (JIS-equivalent supply)
Southeast Asia
Global trading houses referencing JIS

Understanding JIS G3302 is essential to avoid:

Wrong strength supply
Under-spec corrosion resistance
Coating mismatch
Structural misapplication
Procurement confusion when converting between ASTM or EN standards

This guide explains the engineering meaning of JIS grades and how to correctly order material.

1️⃣ What Is JIS G3302?

JIS G3302 covers hot-dip galvanized steel sheet and coil used for:

Roofing
Cladding
Structural sections
Automotive
Appliance panels
Roll formed framing

It is broadly comparable to:

ASTM A653 (USA)
EN 10346 (EU/UK)

But naming conventions differ.

2️⃣ Common JIS Base Steel Grades

The most common JIS G3302 grades are:

Grade	Meaning	Typical Use
SGCC	Commercial quality	Roofing, cladding
SGCD1	Drawing quality	Forming
SGCD2	Deep drawing	Automotive panels
SGCD3	Extra deep drawing	Complex forming
SGCH	High strength	Structural use

2.1 SGCC Explained

SGCC is the most common grade in roofing and light roll forming.

S = Steel
G = Galvanized
C = Commercial
C = Cold rolled base

Characteristics:

Moderate yield strength
Good formability
Suitable for light structural sections

Not ideal for heavy load-bearing purlins unless yield is verified.

2.2 SGCH — High Strength Grade

SGCH is higher strength and more suitable for:

Structural sections
Load-bearing profiles
Stud and track

However, JIS strength classification is less direct than EN structural grades.

Yield must be confirmed via mill certificate.

3️⃣ Coating Mass Classes (Z Coating)

JIS expresses zinc coating mass in g/m² (both sides total).

Common classes:

Designation	Total Coating Mass
Z08	80 g/m²
Z12	120 g/m²
Z18	180 g/m²
Z22	220 g/m²
Z27	275 g/m²

Z27 ≈ 275 g/m² ≈ G90 equivalent.

Z18 ≈ G60 equivalent.

4️⃣ Coating Comparison to ASTM & EN

JIS	Approx. ASTM	Approx. EN
Z18	G60	Z180
Z27	G90	Z275
Z12	G40	Z120

Important:

Do not assume equivalence without verifying coating tolerance.

5️⃣ Mechanical Properties & Roll Forming Impact

Mechanical properties vary by grade and supplier.

Typical SGCC Range:

Yield: ~205–300 MPa
Tensile: ~270–410 MPa

SGCH may exceed 340 MPa yield.

Because strength is not explicitly embedded in grade code like EN S350GD, verification is mandatory.

5.1 Springback Considerations

Higher yield (SGCH):

Increased springback
Requires overbend compensation
Increases shaft load

Commercial SGCC:

Easier forming
Lower forming force
Reduced tool stress

6️⃣ Edge Condition & Slitting

Many JIS coils are supplied slit.

Key considerations:

Burr height control
Edge hardening
High tensile crack sensitivity

Structural roll forming lines must inspect slit edge quality.

7️⃣ Surface Finish Classes

JIS defines surface types:

Regular spangle
Minimized spangle
Skin-passed

Skin-passed coil improves:

Flatness
Paint adhesion
Cosmetic consistency

This is critical for roofing panels.

8️⃣ Thickness & Tolerance

JIS G3302 defines:

Thickness tolerance
Coating mass tolerance
Width tolerance
Flatness standards

Tolerance consistency affects:

Oil canning
Rib height precision
Punch alignment

9️⃣ Corrosion Performance

Approximate service life:

Coating	Typical Use
Z12	Interior/light exposure
Z18	Standard roofing
Z27	Exterior structural

In coastal environments, Z27 minimum recommended.

🔟 Procurement Logic — How to Correctly Order JIS G3302

A complete order should specify:

Example:

JIS G3302 – SGCH – Z27 – 1.2 mm – Slit Edge – Skin Passed – Mill Certificate Required

Breakdown:

Standard
Grade
Coating class
Thickness
Edge condition
Surface finish
Certification

Failure to specify strength leads to uncertainty.

1️⃣1️⃣ Conversion Risks When Importing

Common procurement errors:

Ordering SGCC assuming structural strength
Confusing Z18 with Z27
Not verifying yield strength range
Not requesting coating mass test results
Mixing ASTM and JIS designations in contracts
Not checking revision year of JIS standard

International buyers must align contract language clearly.

1️⃣2️⃣ Machine Design Implications

Switching from:

SGCC → SGCH
Z18 → Z27

Changes:

Springback behavior
Tooling load
Coating thickness at bends
Friction profile

Higher tensile SGCH behaves closer to S320GD / Grade 50 material.

1️⃣3️⃣ Buyer Strategy (30%)

When SGCC Is Suitable

Roofing panels
Light cladding
Flashing
Non-structural profiles

When SGCH Is Required

Structural framing
Load-bearing sections
Stud & track
Solar mounting

When to Specify Z27

Coastal exposure
Long-term exterior life
Commercial roofing warranties

Cost Considerations

Z27 costs more than Z18.

Higher strength grades may:

Allow thinner gauge
Reduce steel weight
Offset material cost

Engineering-based selection improves profitability.

6 Frequently Asked Questions

1. What is SGCC?

A commercial-grade galvanized steel under JIS G3302, commonly used for roofing and light forming.

2. Is SGCH structural?

Yes, it is higher strength than SGCC but yield must be verified.

3. What is Z27 equivalent to?

Approximately G90 (ASTM) or Z275 (EN).

4. Can SGCC be used for purlins?

Not recommended unless yield strength meets structural requirements.

5. Does coating class affect forming?

Yes. Higher coating mass slightly affects bend radius and surface cracking behavior.

6. Should I request mill test certificates for JIS coil?

Yes. Mechanical properties are not fully defined by grade code alone.

Final Engineering Summary

JIS G3302 governs galvanized steel coil widely used in Asian markets.

Key differences compared to ASTM and EN:

Grade code does not directly embed yield strength
Coating classes expressed in g/m²
Strength must be verified via certification

Correct procurement requires:

Grade clarity
Coating mass confirmation
Mechanical property verification
Surface and edge specification

Understanding JIS G3302 prevents structural misapplication and corrosion underperformance in roll forming production.