SGCC vs SGCD1 – Zusammensetzung, Wärmebehandlung, Eigenschaften und Anwendungen

Introduction

SGCC and SGCD1 are two commonly specified galvanized steel sheet grades used throughout automotive, appliance, building, and general fabrication industries. Engineers and purchasing professionals frequently weigh corrosion protection and cost against formability and in-service strength when selecting between them. Typical decision contexts include: choosing a lower-cost, general-purpose galvanized sheet for non-critical panels (SGCC) versus selecting a deep-drawing-capable coated sheet for complex forming and stretch operations (SGCD1).

The primary practical distinction between SGCC and SGCD1 lies in their chemistry and processing intent: SGCD1 is formulated and processed for enhanced cold formability (lower effective carbon and tighter control of impurity/microalloying) whereas SGCC is a general commercial-quality galvanized product with composition and properties optimized for broad, economical use. Because both are galvanized products intended for similar applications, direct comparisons often focus on composition-driven differences in formability, hardenability, weldability, and final mechanical properties.

1. Standards and Designations

• JIS (Japan): SGCC, SGCD1 are JIS designations for hot-dip galvanized steel sheet and strip. They appear in JIS G3302 (hot-dip galvanized steel sheet and strip) and related JIS cold-rolled base steel standards (e.g., JIS G3141 for cold-reduced carbon steel).
• EN (Europe): Equivalent functions are carried by DX51D / DX53D / DX54D categories for galvanized steel sheet (EN 10346 / EN 10142 / EN 10152 family); specific grade mapping depends on mechanical and surface requirements rather than identical nomenclature.
• ASTM/ASME: ASTM does not use SGCC/SGCD names; comparable materials would be commercial-quality and deep-drawing quality cold-rolled steels that are subsequently galvanized to meet ASTM A653 (Zinc-coated (galvanized) steel sheet) or A527 families.
• GB (China): GB/T standards use different grade codes (e.g., SGCC appears in some translated Chinese standards as well). Verify local standard equivalents.

Classification: both SGCC and SGCD1 are carbon (low-carbon) steels (not stainless, alloy, or HSLA). SGCD1 is a drawing-grade low-carbon galvanized steel designed for superior formability; SGCC is a commercial-quality galvanized steel.

2. Chemical Composition and Alloying Strategy

The following table gives indicative composition ranges (wt%). These are representative ranges typical for JIS-style commercial and drawing grades—actual mill specifications and standard limits should be checked on mill test certificates.

Element	SGCC (typical range, wt%)	SGCD1 (typical range, wt%)
C	0.02 – 0.12	0.02 – 0.10 (lower target for formability)
Mn	0.10 – 0.60	0.10 – 0.60
Si	0.02 – 0.30	≤ 0.10 (kept low for surface and drawability)
P	≤ 0.05 (controlled)	≤ 0.03 – 0.05 (tighter control desirable)
S	≤ 0.05 (reduced)	≤ 0.02 – 0.03 (lower preferred)
Cr	Typically < 0.10	Typically < 0.05
Ni	Typically < 0.10	Typically < 0.05
Mo	Typically < 0.05	Typically < 0.03
V, Nb, Ti	Absent or trace	Usually absent; microalloying uncommon
B	Trace if present	Trace if present
N	Trace	Trace

How alloying affects properties: - Carbon: Primary determinant of strength and hardenability. Lower carbon improves ductility and stretch/formability (advantage SGCD1). Higher carbon increases strength but reduces deep-draw capability. - Manganese and silicon: Added to increase strength and deoxidation control. Excess Si/Mn can adversely affect coating adhesion and forming; SGCD1 often specifies lower Si. - Phosphorus/sulfur: Impurities that can embrittle grain boundaries and reduce ductility; drawing grades enforce tighter limits or use additional processing to control these. - Microalloying (V, Nb, Ti): Generally not used in these commercial galvanized grades; their presence would increase strength and hardenability but can compromise deep drawability.

3. Microstructure and Heat Treatment Response

Typical microstructures: - Both SGCC and SGCD1, in their as-supplied cold-rolled and annealed forms, are largely ferritic with a fine-grain ferrite matrix and small amounts of pearlite or bands of interstitial phases depending on processing. - SGCD1 is annealed with processing aimed at minimizing banding, promoting uniform microstructure and fine grain size to maximize formability.

Heat treatment response: - These are low-carbon steels not designed for quench-and-temper hardening. Typical processing routes are cold reduction followed by continuous annealing or batch annealing (recrystallization anneal). - Normalizing or quench & temper is not commonly applied to these grades; thermal processing will only modestly alter strength and ductility. Thermo-mechanical processing at the mill (controlled rolling followed by anneal) can refine grain size and improve the strength–ductility balance. - SGCD1 benefits from more controlled annealing cycles (e.g., tension leveling and recrystallization anneal) to ensure excellent surface quality and consistent stretch-flange behavior.

4. Mechanical Properties

The table below summarizes typical mechanical property ranges for commercially supplied galvanized SGCC and SGCD1 sheets. Values depend strongly on thickness, cold-rolling reduction, and annealing schedule; these are indicative.

Property	SGCC (typical)	SGCD1 (typical)
Tensile strength (MPa)	~270 – 410	~260 – 410 (similar upper bound)
Yield strength (0.2% offset, MPa)	~205 – 350	~170 – 300 (lower yield for deep draw)
Elongation (%)	~20 – 40	~28 – 45 (higher ductility for drawing)
Impact toughness	General-purpose; moderate	Comparable or slightly improved due to refined anneal
Hardness (HB or HV)	Low to moderate	Typically lower or similar, optimized for forming

Interpretation: - SGCD1 is optimized to lower effective yield strength and increase elongation to accommodate deep drawing and stretch forming without cracking; tensile ultimate strengths can be similar to SGCC depending on temper. - SGCC is a cost-effective general-grade with broader, less tightly controlled mechanical ranges—suitable where extreme formability is not required.

5. Weldability

Weldability of galvanized low-carbon steels is generally good, but coating and composition affect practice.

Key factors: - Carbon content and hardenability influence cold cracking susceptibility—lower carbon and lower effective hardenability improve weldability and reduce preheat requirements. - Residual coating (zinc) produces fume and can lead to brittle intermetallics in the weld toe if not managed; proper welding procedures (remove coating at welds, use proper ventilation and filler metals) are needed.

Useful carbon-equivalent formulas to assess crack sensitivity: - IIW carbon equivalent: $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - International Pcm: $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$

Qualitative interpretation (no numeric calculation here): - Both grades generally yield low $CE_{IIW}$ and $P_{cm}$ values because they are low-carbon, low-alloy steels, so they are readily weldable with common welding processes. - SGCD1, with its tighter control of carbon, Si, and P/S, can present marginally better resistance to cold-cracking in restrained weld joints versus SGCC. - Galvanized coating necessitates surface prep: remove zinc from welding zone or adopt process controls to mitigate zinc vapor and porosity.

6. Corrosion and Surface Protection

• Neither SGCC nor SGCD1 is stainless; both rely on zinc coating (hot-dip galvanizing) for corrosion protection. The coating provides sacrificial protection and a barrier.
• Typical surface protection and finishing options:
• Hot-dip galvanizing (as the grade implies) provides robust atmospheric corrosion resistance.
• Post-treatment: passivation, chromate-free conversion coatings, painting, or coil coating can be applied to extend life and improve aesthetics.
• PREN (pitting resistance equivalent number) is only relevant for stainless alloys and not applicable to SGCC/SGCD1 because they are not stainless steels: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
• Practical note: Deep-drawing operations (SGCD1) require careful control of coating adhesion and lubricants to avoid coating flaking or cracking in severe forming; some manufacturers supply specifically treated galvanneal or electro-galvanized variants for painting/forming compatibility.

7. Fabrication, Machinability, and Formability

• Formability: SGCD1 is designed for deep drawing and complex forming—higher total elongation, lower yield strength, and optimized surface oxides support extended draws and stretch flanging. SGCC performs well for bending and light forming but is not optimized for severe draws.
• Cutting and shearing: Both grades behave similarly in blanking, shearing, and laser cutting. Zinc coating can affect burr formation and tool wear; tooling may require more frequent maintenance for coated steels.
• Machinability: These are low-carbon steels with good machinability in general; coating and thin gauges are more relevant than base steel for machining operations. Cutting fluids must handle zinc-contaminated chips.
• Finishing: Paint adhesion is typically good after appropriate pretreatment. Coil coatings and polymer topcoats are commonly applied; however, formability of the coated product must be validated for SGCD1 to prevent coating fracture.

8. Typical Applications

SGCC (common uses)	SGCD1 (common uses)
Building siding, roofing panels, gutters, HVAC ducts	Automotive inner panels, outer body panels with deep draw features
Appliance cabinet panels where extensive forming is not required	Complex-shaped appliance components (e.g., drum housings) requiring stretch forming
General fabrication, shelving, sign frames	Electrical enclosures with drawn features; stamped parts with tight radius
Structural light-gauge sections where low cost is primary	Components requiring high surface continuity after forming

Selection rationale: - Choose SGCC when cost, readily available stock, and general corrosion protection are primary concerns and parts do not require severe forming. - Choose SGCD1 when deep drawing, stretch forming, or complex stamping is required and where minimizing fracture and achieving consistent surface after forming are critical.

9. Cost and Availability

• Cost: SGCC is typically the lower-cost option because its chemistry and processing tolerances are broader. SGCD1 commands a modest premium due to tighter process control and annealing optimized for drawability.
• Availability: Both grades are widely available in coil and sheet form from major mills. SGCC as a general-purpose galvanized product is commonly stocked in many gauge/thickness combinations; SGCD1 may be less stocked in some regions and more commonly sourced to order in specific temper/anneal conditions.
• Product forms: coils, cut-to-length sheets, slitted coils, and pre-painted/coil-coated variants.

10. Summary and Recommendation

Summary table (qualitative)

Attribute	SGCC	SGCD1
Weldability	Good; standard practices for galvanized steel	Slightly better due to lower C & impurities
Strength–Toughness balance	Moderate; general-purpose	Tuned for higher ductility and lower yield (better formability)
Cost	Lower (economical)	Slightly higher (premium for formability)

Recommendations: - Choose SGCC if you need a cost-effective, general-purpose galvanized sheet for parts that require moderate forming, strong corrosion protection, and broad availability (e.g., roofing, ducts, basic panels). - Choose SGCD1 if your application requires deep drawing, significant stretch forming, excellent surface quality after severe forming, or where minimizing edge and flange cracking is critical (e.g., automotive inner panels, complex stamped appliance parts).

Final practical note: SGCC and SGCD1 are close cousins in the galvanized steel family. The correct choice depends primarily on the required forming severity and surface/paint finishing expectations. Always verify the mill test certificate and sample-form key components where severe forming or critical welding is involved.