SPCC vs SGCC:
Which Steel Grade
for Your Part?

What SPCC and SGCC Actually Are

Both grades are defined under JIS (Japanese Industrial Standards), which are widely adopted across Vietnamese and Asian manufacturing.

Side-by-Side Comparison

Property	SPCC	SGCC
Base material	Cold-rolled steel	Cold-rolled steel + zinc coating
Zinc coating	None	Z12–Z27 (120–275 g/m²)
Corrosion resistance (bare)	Low — rusts quickly without coating	Good — zinc sacrificial protection
Surface finish	Smooth, matte grey	Spangle pattern or zero-spangle
Powder coat adhesion	Excellent after phosphate pre-treatment	Good — zinc surface requires correct pre-treatment
Weldability (MIG/TIG)	Excellent	Moderate — zinc fumes require ventilation; porosity risk
Laser cutting	Clean edge, no spatter issues	Acceptable — zinc vapour affects edge quality at higher speeds
Bending	Good springback behaviour	Slight coating delamination risk at tight bend radii
Material cost	Lower	Higher (zinc processing cost)
Typical thickness range	0.4 – 3.2 mm	0.4 – 2.3 mm

Corrosion Resistance in Detail

SGCC provides corrosion resistance through two mechanisms: the zinc coating acts as a physical barrier, and when the coating is scratched, zinc sacrificially corrodes to protect the underlying steel. This makes SGCC significantly more durable in humid, outdoor, or salt-air environments.

SPCC with powder coating can match SGCC in corrosion resistance for most indoor applications — provided the phosphate pre-treatment is done correctly and the coating film thickness is adequate (≥60 μm). For outdoor or high-humidity environments, SGCC with powder coat provides a more reliable long-term result because the zinc layer remains active even if the coating is chipped.

Welding Considerations

This is the most common area where SGCC causes problems in production. The zinc coating burns off during welding and produces zinc oxide fumes, which create two issues:

• Porosity in the weld bead, reducing joint strength
• Health hazard — requires adequate fume extraction

For assemblies with significant welding (enclosures, frames, brackets with many weld points), SPCC followed by powder coating is usually the better production choice. SGCC is preferred when welding is minimal or where bare-metal corrosion protection at cut edges is needed.

Powder Coating on SGCC vs SPCC

Both grades accept powder coating well, but the pre-treatment chemistry differs. SPCC typically goes through an iron phosphate or zinc phosphate bath. SGCC requires a chromate or non-chrome passivation step to prepare the zinc surface for paint adhesion.

At Vu Trinh, our 5-stage pre-treatment line handles both SPCC and SGCC correctly. However, mixing both grades in a single batch requires attention to the passivation stage — something that should be confirmed with your fabricator before ordering.

When to Use Each Grade

Use Case	Recommended Grade	Reason
Indoor enclosures, cabinets	SPCC + powder coat	Lower cost, excellent coating result
Outdoor equipment housings	SGCC + powder coat	Zinc layer protects cut edges and chips
Heavy-weld assemblies	SPCC	No zinc fume, cleaner weld bead
Light-gauge structural parts (no coating)	SGCC	Bare corrosion resistance during transit/storage
Parts with tight bend radii (<1t)	SPCC	No risk of coating delamination at bend
Cost-sensitive high volume (indoor)	SPCC	Material cost advantage at scale

How to Specify on Your Drawing

When specifying steel grade on a technical drawing, use the JIS designation with coating weight where applicable:

• SPCC-SD — standard surface, dull finish (most common for powder coating)
• SGCC Z18 — galvanized, 180 g/m² zinc (general industrial)
• SGCC Z27 — galvanized, 275 g/m² zinc (higher corrosion resistance)

If you are unsure which grade is appropriate for your application, include it as a question in your RFQ. Our engineering team reviews drawings before quoting and will flag if a grade substitution would reduce cost or improve performance.