JIS G 3302 Hot-Dip Galvanized Steel

1. Definition and Scope

JIS G 3302 is the Japanese Industrial Standard specifying hot-dip zinc-coated steel sheet and strip produced by the continuous galvanizing process. It covers material in thicknesses from 0.25 mm to 3.2 mm, supplied in coils or cut lengths, intended for further cold forming including roll forming, press working, and bending. JIS G 3302 is the primary galvanized feedstock standard in Japan, Korea, Taiwan, and Southeast Asian roll forming markets, parallel in function to ASTM A653 in North America and EN 10346 in Europe.

The standard defines soft (commercial/drawing) grades on cold-reduced base metal — SGCC, SGCD (drawing classes), and SGCH — plus high-strength structural grades SGC340/400/440/490/570 (cold-reduced) and SGH340/400/440/490/540 (hot-rolled). Each grade is combined with a coating mass designation (Z06 through Z45) indicating the total zinc coating mass on both surfaces in g/m². Mechanical properties, coating adherence, and surface quality requirements are specified for each grade. Test sample orientation is longitudinal to rolling direction, matching the primary forming axis on roll forming lines. Japanese mill shipment documents include English-language inspection certificates for export orders, facilitating direct use by roll forming plants in Southeast Asia without re-testing on receipt.

Roll forming manufacturers in Asia specify JIS G 3302 on purchase orders using the grade name, coating designation, dimensions, and surface treatment. Finished profile dimensional tolerances for export markets may additionally reference EN 10162 or JIS-derived tolerances depending on customer requirements. The standard requires coating adherence testing on every production batch and reports results on the inspection certificate accompanying each shipment. Coil inner diameter of 508 mm or 610 mm is standard for compatibility with roll forming decoiler mandrels.

2. Steel Grades

JIS G 3302 organizes grades by base metal and application: soft commercial/drawing grades (SGCC, SGCD, SGCH) for general forming, and high-strength structural grades (SGC* cold-reduced and SGH* hot-rolled) with defined minimum yield strength.

2.1 Soft Steel Grades (Commercial and Drawing)

2.2 High-Strength Structural Grades (SGC / SGH)

2.3 Grade Comparison with International Standards

3. Coating Mass and Quality

JIS G 3302 coating mass designations express the total mass of zinc coating on both surfaces in g/m². The designation number equals this total mass value.

3.1 Coating Mass Designations

3.2 Coating Adherence and Bend Test

Roll forming bend outer radii that meet or exceed the JIS bend test mandrel diameter produce coating behavior within standard acceptance. Micro-cracking on outer bend surfaces at radii below the test mandrel is normal and does not indicate coating failure if no flaking occurs.

Coating mass measurement per JIS G 3302 uses gravimetric methods on test samples or magnetic induction instruments for non-destructive verification. Mill shipment documents report average coating mass per coil. Roll forming does not measurably reduce coating mass on flange surfaces; cut edges at the cutoff station expose uncoated steel and benefit from touch-up galvanizing or zinc-rich paint in aggressive exposure applications. Warehouse inventory rotation follows first-in-first-out by coil receipt date to minimize coil set increase from long storage periods exceeding six months.

4. Mechanical Properties

Mechanical properties are measured on the coated product after hot-dip galvanizing. The coating process involves heating to approximately 450–460°C, which may alter substrate properties compared to the original cold-rolled condition.

4.1 Thickness Tolerance (JIS G 3302 Table 3)

4.2 Width Tolerance

5. Surface Finish and Treatment

JIS G 3302 specifies surface finish categories and post-coating treatment that affect roll forming friction and finished appearance.

5.1 Surface Treatment

6. Designation System

JIS G 3302 product designation combines grade, coating mass, surface finish, surface treatment, dimensions, and standard reference.

6.1 Worked Designation Examples

7. Roll Forming Process Considerations

JIS G 3302 coated strip requires roll surfaces compatible with zinc coating to avoid galling and surface marking. Chrome-plated or polished tool steel rolls are standard. Roll gap adjustment follows the same practice as other coated steels: set to measured coil thickness at entry, verify profile dimensions on first 3–5 pieces.

7.1 Forming Parameters by Grade

7.2 Roll Surface and Lubrication

Pre-punching on JIS G 3302 feedstock before roll forming requires punch clearance of 10–15% of strip thickness per side. Coating buildup on punch edges is cleared at intervals proportional to coating mass; Z27 and heavier coatings require more frequent punch maintenance than Z12 on equivalent production volume. Hole edge coating fracture is acceptable per JIS bend test criteria provided no flaking occurs; touch-up is applied on exterior architectural profiles after forming and cutoff.

8. Roll Forming Applications

JIS G 3302 galvanized strip is the standard feedstock for roll forming production across Japanese and Asian building, industrial, and infrastructure markets.

Export roll-formed profiles produced from JIS G 3302 feedstock for European or North American markets are typically certified against the destination standard on the finished product (EN 10162 dimensional tolerances, CE marking requirements) while the feedstock traceability chain references the JIS mill test certificate.

8.1 Packaging and Storage Requirements