SGCD1 vs SGCD2 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
SGCD1 and SGCD2 are closely related low‑carbon steels commonly specified for forming, stamping, and cold‑finishing operations in automotive, appliance, and light‑engineering sectors. Engineers and procurement professionals choosing between them weigh tradeoffs such as formability versus strength, weldability versus post‑forming heat treatment capability, and unit cost versus availability.
The primary operational distinction between the two grades lies in their intended forming performance: one grade is optimized for higher cold‑forming ductility and consistent sheet/strip drawability, while the other sacrifices some forming ease to gain higher strength and improved hardenability. Because these grades are used interchangeably in many fabrication environments, a careful comparison of composition, microstructure response, mechanical properties, and fabrication considerations is essential for correct selection.
1. Standards and Designations
- Major standards and families relevant to SGCD‑type steels:
- ASTM/ASME (AISI/SAE designations for carbon and low‑alloy steels)
- EN (European EN 10025/EN 10130 categories for cold‑rolled steels and structural grades)
- JIS (Japanese Industrial Standards for cold‑rolled and deep‑drawing steels)
- GB (Chinese national standards including cold‑rolled sheet and strip categories)
- Classification: SGCD1 and SGCD2 are best categorized as low‑carbon, cold‑forming steels within the carbon‑manganese family (not stainless, not tool steels, and generally not HSLA by modern definition). They are intended primarily for forming and fabrication rather than high‑temperature service or heavy alloyed structural applications.
- Note: Designation schemes vary by region and mill; comparable equivalents in ASTM/EN/GB/JIS catalogs should be confirmed by chemistry and mechanical property certificates.
2. Chemical Composition and Alloying Strategy
The two grades are formulated to balance low carbon for ductility and enough manganese/silicon (and occasional microalloying) to provide strength and process stability. Actual limits vary by supplier and regional standard; the following table lists representative, typical ranges. Always confirm composition from the mill test certificate for design calculations.
| Element | Typical range (wt%) — SGCD1 (representative) | Typical range (wt%) — SGCD2 (representative) |
|---|---|---|
| C | 0.04 – 0.12 | 0.06 – 0.18 |
| Mn | 0.20 – 0.80 | 0.30 – 1.00 |
| Si | 0.02 – 0.25 | 0.02 – 0.30 |
| P | ≤ 0.030 (max) | ≤ 0.030 (max) |
| S | ≤ 0.020 (max) | ≤ 0.020 (max) |
| Cr | trace – 0.20 (if present) | trace – 0.30 (if present) |
| Ni | trace – 0.20 (if present) | trace – 0.30 (if present) |
| Mo | typically absent or ≤ 0.05 | occasionally ≤ 0.10 |
| V, Nb, Ti, B | usually absent; microalloying possible in some variants | microalloying possible for strength control |
| N | trace | trace |
Explanation: - SGCD1 typically targets the lower end of carbon and alloying to maximize cold formability and minimize hardenability. Lower C and controlled Mn reduce the risk of forming‑induced shear fractures and thinning. - SGCD2 accepts modestly higher carbon and alloying (or microalloying additions) to increase yield/tensile strength and response to heat treatment or tempering. These changes increase hardenability and may slightly reduce formability. - Trace additions of Cr, Ni, or V are sometimes used in SGCD2 variants to tune strength, toughness, and temper response without moving into the alloy steel domain.
3. Microstructure and Heat Treatment Response
- Typical microstructures after standard processing:
- SGCD1: Predominantly ferritic matrix with fine pearlite islands when carbon approaches higher values in the grade range. Grain refinement and clean inclusion control are emphasized to improve stretchability and hole expansion.
- SGCD2: Ferrite–pearlite structure with a higher fraction of pearlite or tempered bainite (if thermomechanical processing or heat treatment is applied) depending on alloy content and cooling rate.
- Heat treatment effects:
- Normalizing: Promotes a uniform ferrite‑pearlite distribution. SGCD2, with slightly higher alloy content, will show modestly higher hardenability after normalizing.
- Quenching & tempering: Not typically applied to SGCD1 because it would negate the forming advantages. SGCD2 variants with microalloying can be hardened/tempered to raise strength for load‑bearing components.
- Thermo‑mechanical processing (TMP): Both grades benefit from controlled rolling and coiling schedules. TMP can refine grain size, improving a balance of strength and ductility—useful for SGCD2 when higher strength without sacrificing all formability is required.
4. Mechanical Properties
The following table gives representative mechanical property ranges for typical product forms (cold‑rolled sheet or strip). Verify exact values with product specification and testing.
| Property | SGCD1 (typical) | SGCD2 (typical) |
|---|---|---|
| Tensile strength (MPa) | 270 – 390 | 320 – 480 |
| Yield strength (0.2% offset, MPa) | 150 – 260 | 200 – 350 |
| Elongation (%), A50mm or A5 | 28 – 40 | 20 – 30 |
| Impact toughness (J) | moderate — higher at room temp; varies with thickness | moderate — may be lower than SGCD1 at equal thickness |
| Hardness (HB) | ~100 – 150 | ~120 – 190 |
Interpretation: - SGCD2 tends to show higher tensile and yield strengths at the expense of ductility and formability due to higher carbon/alloying and possible microalloy additions. - SGCD1 emphasizes elongation and stretch formability, delivering better hole expansion and resistance to fracture in severe drawing operations. - Impact toughness depends on cleanliness, thickness, and processing; with equivalent processing, SGCD1 generally provides a more ductile fracture mode.
5. Weldability
Weldability is primarily controlled by carbon content, effective alloying (which increases hardenability), and the presence of residuals. Useful predictive indices include the IIW carbon equivalent and the Pcm formula:
$$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$
$$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - SGCD1: Lower carbon and fewer hardenability elements yield lower $CE_{IIW}$ and $P_{cm}$ values, indicating easier weldability, reduced preheat requirements, and lower risk of cold‑cracking. - SGCD2: Elevated carbon/manganese and possible microalloying slightly increase $CE_{IIW}$/$P_{cm}$, so weld procedures may need higher preheat, controlled heat input, or tempering of the HAZ in thicker sections. - Practical note: For both grades, shop practice (joint design, consumable selection, interpass temperature) governs success. Always qualify welding procedure specification (WPS) with appropriate testing for critical assemblies.
6. Corrosion and Surface Protection
- These grades are non‑stainless low‑carbon steels; corrosion resistance is typical of plain carbon steel.
- Surface protection strategies:
- Hot‑dip galvanizing, electrogalvanizing, and pre‑treatment followed by paint or powder coating are the primary protections for atmospheric and mild corrosive environments.
- For environments requiring better corrosion resistance, consider conversion coatings, duplex coatings, or switching to stainless steel families—PREN is not applicable here since these are not stainless grades.
- When chromia or nickel additions are present at trace levels (SGCD2 variants), they do not significantly change atmospheric corrosion resistance compared to standard protective systems.
7. Fabrication, Machinability, and Formability
- Formability:
- SGCD1: Optimized for deep drawing, stretch forming and tight‑radius bending. Lower carbon and controlled inclusion morphology give superior hole expansion ratio and reduce springback variability.
- SGCD2: Better for applications requiring higher retained strength after forming; formability is acceptable for moderate drawing but limited for extreme deformation.
- Machinability:
- Both are relatively machinable when annealed or in the as‑supplied soft condition; SGCD2 may show slightly higher tool wear due to increased pearlite or microalloy precipitates.
- Finishing:
- Surface condition matters for coating adhesion and painted finishes—specify appropriate pickling, phosphating, or cleaning to suit downstream processes.
8. Typical Applications
| SGCD1 (typical uses) | SGCD2 (typical uses) |
|---|---|
| Deep‑drawn automotive inner panels, appliance shells, complex stamped parts requiring high stretchability | Structural pressings, reinforcement brackets, formed parts that require higher yield strength or limited post‑forming heat treatment |
| Tubes and sections requiring good bendability | Cold‑formed load‑bearing components, medium‑duty shafts (after heat treatment) |
| Consumer products where surface finish and formability are priorities | Parts that require trimming, moderate machining, and higher strength-to-weight within carbon steel limits |
Selection rationale: - Use SGCD1 when the manufacturing process includes severe drawing, hole expansion, or when minimizing forming cracks is paramount. - Use SGCD2 when the final part requires higher strength or improved performance after thermal processing and when forming operations are moderate.
9. Cost and Availability
- Relative cost:
- SGCD1 is generally cost‑competitive due to lower alloy content and simpler processing requirements.
- SGCD2 may carry a modest premium if microalloying or additional processing (e.g., controlled rolling, tempering) is used.
- Availability:
- Both grades are commonly available in cold‑rolled sheet, strip, and sometimes pickled and oiled coils from regional mills. Product forms (tolerance, thickness, surface finish) vary by mill and region; lead times for specialized tempers or ultraclean surface conditions can be longer.
10. Summary and Recommendation
| Characteristic | SGCD1 | SGCD2 |
|---|---|---|
| Weldability | Better (lower C, lower CE) | Good to conditional (higher CE, may need preheat) |
| Strength–Toughness balance | Prioritizes toughness and ductility | Prioritizes higher strength with reasonable toughness |
| Cost | Lower | Slightly higher (depending on microalloying/process) |
Recommendations: - Choose SGCD1 if your part requires high cold‑formability, deep drawing, excellent hole expansion, and simple weld procedures. It is well suited for thin‑gauge panels, consumer appliance shells, and components where surface finish and ductility dominate design drivers. - Choose SGCD2 if your application requires higher as‑formed strength, improved load‑bearing capacity, or the option for post‑forming hardening/tempering. SGCD2 is suitable for formed structural brackets, components subject to higher in‑service stress, or where a higher strength floor is needed without moving to heavier alloy classes.
Final note: The ranges and behaviors summarized here are representative. Because nomenclature, composition limits, and process routes vary by mill, always request mill test certificates (MTC), confirm applicable standards, and run forming/welding trials for critical components before release to production.