SPCD vs SPCE – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
SPCD and SPCE are two commonly specified cold-rolled low-carbon steel grades used for sheet-metal applications where formability and consistent surface quality are required. Procurement and design teams frequently weigh trade-offs such as formability versus strength, production yield versus post-processing cost, and weldability versus the risk of strain-induced cracking. The selection dilemma typically appears when designers must choose between a grade optimized for deeper drawing and a grade that balances moderate drawing performance with higher strength.
The primary functional distinction between the two grades lies in their suitability for progressively more severe forming operations: one is tailored for severe deep-drawing (higher formability, lower carbon/hardenability), while the other provides better balance between drawing and strength (slightly higher carbon or microalloying to increase strength and springback control). This makes them commonly compared in automotive inner parts, household appliances, and precision-formed components.
1. Standards and Designations
Major standards and how these grades are classified: - JIS (Japan): The SPC family (SPCC, SPCD, SPCE, SPFC, etc.) appears in JIS G3141 for commercial-quality cold-reduced steel sheets and strips for cold forming. - EN (Europe): Equivalent functional classes are normally covered under EN 10130 (cold rolled low carbon steels — commercial and drawing qualities) or EN 10139 for cold-rolled, high-quality steels, but direct one-to-one letter-for-letter mapping is not exact. - ASTM/ASME: ASTM does not use the SPC letter codes; cold-rolled mild steels are typically referenced by UNS numbers or ASTM A1008/A1049 classifications. - GB (China): GB/T standards have their own designations but often supply "deep drawing" or "extra deep drawing" grades with comparable roles.
Classification: - SPCD: Cold-rolled low-carbon steel intended for drawing; considered a carbon steel (non-stainless, non-alloy) with low to moderate formability emphasis. - SPCE: Cold-rolled low-carbon steel formulated for extra-deep drawing (higher formability, lower carbon/hardenability) — also a carbon steel, but with chemistry and process control tuned to maximize ductility and minimize yield-point elongation and surface defects.
2. Chemical Composition and Alloying Strategy
The SPC family are low-carbon cold-reduced steels. Exact chemical limits vary by standard and producer; the following table summarizes the typical alloying intent and relative levels rather than absolute limits (consult the relevant standard or mill certificate for precise values).
| Element | SPCD (typical level & intent) | SPCE (typical level & intent) |
|---|---|---|
| C | Low — controlled for moderate strength and formability | Very low — optimized for enhanced formability and lower hardenability |
| Mn | Low–moderate — deoxidation and strength contribution | Low–moderate — kept low enough to preserve ductility |
| Si | Trace–low — deoxidation; limited to control strength | Trace–low — similar role, minimized where required for formability |
| P | Trace — controlled for surface quality | Trace — controlled to minimize embrittlement |
| S | Trace — controlled to enhance machinability if present | Trace — minimized to avoid formability issues |
| Cr, Ni, Mo, V, Nb, Ti, B | Typically not significant — may be present in trace amounts if microalloying is used for specific properties | Typically minimal to absent; SPCE aims to avoid elements that raise hardenability |
How alloying affects performance: - Carbon increases strength and hardenability but reduces ductility and severe-drawing performance. SPCE is formulated with lower carbon to maximize drawability. - Manganese contributes to strength and toughness but excessive Mn raises hardenability and reduces deep-draw capability; it is balanced carefully. - Microalloying (V, Nb, Ti) can be used in closely related grades to refine grain size and improve strength without major loss of formability; these additives are used sparingly in the SPC family because they can reduce stretchability in extreme forming.
3. Microstructure and Heat Treatment Response
Typical microstructures: - Both SPCD and SPCE are supplied as cold-rolled and usually annealed (recrystallized) to obtain a uniform ferritic microstructure with fine grains. The dominant phase is ferrite with low dislocation density after appropriate anneal. - SPCE will typically be processed to produce a very clean, fully recrystallized ferritic microstructure with minimal strain aging and low yield-point elongation to support deep drawing. - SPCD may have a similar ferritic microstructure but with slightly higher dislocation density or microalloy precipitates if the mill targets higher yield or strength.
Heat treatment response and processing routes: - Annealing: Both grades respond well to full anneal and continuous anneal cycles; SPCE often requires stricter control of anneal temperature and cooling rate to avoid strain aging. - Normalizing, quench & temper: These are not commonly applied to cold-rolled drawing steels because the intent is to preserve good surface finish and formability; these treatments are used in other structural steels to increase strength. - Thermo-mechanical treatments: Not typical for standard SPCD/SPCE sheets; special variants with microalloying and controlled rolling would be classified differently and have different designations.
4. Mechanical Properties
The mechanical properties of cold-rolled drawing steels depend strongly on temper (skin-pass, temper-rolled, fully-annealed). Rather than absolute numbers, the table below gives comparative expectations; for design or procurement, always use mill test certificates or specific standard subgrades.
| Property | SPCD (relative) | SPCE (relative) |
|---|---|---|
| Tensile strength | Moderate — higher than SPCE in many mill tempers | Lower — optimized to prioritize elongation over strength |
| Yield strength | Moderate — provides better springback control in forming | Lower — lower yield to enable deep draws with minimal cracking |
| Elongation (%) | Good — suitable for moderate drawing | Very good — superior elongation and necking resistance |
| Impact toughness | Adequate at room temp — not typically specified for low-temp service | Adequate — similar to SPCD unless specially alloyed |
| Hardness | Low to moderate (soft-annealed to temper-rolled) | Low (soft-annealed to maximize ductility) |
Which is stronger, tougher, or more ductile: - Strength: SPCD typically exhibits modestly higher strength or yield than SPCE when both are in comparable tempers. - Ductility/formability: SPCE provides superior ductility and deep-drawing capability because of lower carbon and careful annealing; it is less prone to cracking during extreme forming. - Toughness: Both grades have comparable toughness at room temperature; differences are generally small and overshadowed by changes in process history.
5. Weldability
Weldability of low-carbon cold-rolled steels in the SPC family is generally good due to their low carbon and low alloy content. Key considerations: - Carbon content and combined hardenability determine susceptibility to cold cracking. Lower carbon (as in SPCE) reduces risk; higher effective carbon increases preheat/postheat needs. - Microalloying elements (if present) can increase hardenability locally at the weld heat-affected zone and raise cracking risk.
Useful carbon-equivalent formulae for qualitative weldability assessment: - International Institute of Welding (IIW) carbon equivalent: $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - International parameter $P_{cm}$ used in Europe for weldability judgment: $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Interpretation: - Lower $CE_{IIW}$ and $P_{cm}$ indicate easier weldability with standard processes and less need for preheat. SPCE, due to lower carbon and minimal alloying, will normally score lower and therefore require less welding mitigation than SPCD when comparing like tempers. - For critical assemblies (automotive safety parts), follow welding procedure qualifications and refer to mill certificates for exact chemical composition.
6. Corrosion and Surface Protection
- Neither SPCD nor SPCE are stainless steels; their corrosion resistance is that of low-carbon steel and requires surface protection for most exposed applications.
- Typical protections: hot-dip galvanizing (both continuous and batch), electro-galvanizing, zinc-nickel plating, phosphate plus paint systems, or organic coatings such as powder coating.
- When quoting protective performance indexes like PREN, note that: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ is applicable only to stainless alloys; it is not meaningful for SPCD/SPCE (which lack sufficient Cr, Mo, and N to qualify as stainless).
- Selection: For formability-critical parts that need corrosion protection, choose coating processes compatible with deep drawing (e.g., pre-coated or electro-galvanized for limited stretching; special lubrication and thinner zinc layers for higher draw ratios).
7. Fabrication, Machinability, and Formability
- Cutting and shearing: Both grades cut and shear readily in typical processing; SPCE may require tighter control of blanking clearance for high-draw applications because of its lower yield and higher elongation behavior.
- Bending and springback: SPCD’s slightly higher yield can make springback more repeatable; SPCE’s lower yield results in less force to form but can require compensation for springback in precision parts.
- Deep drawing/forming: SPCE is preferred for multi-stage deep drawing, ironing, or complex geometries due to its higher uniform elongation and reduced tendency for earing or fracturing.
- Machinability: Both are similar to mild steels; SPCE’s lower strength can marginally improve machinability but differences are small.
- Surface finish: SPCE processing emphasizes cleanliness and low inclusions to prevent surface defects during severe forming.
8. Typical Applications
| SPCD — Typical Uses | SPCE — Typical Uses |
|---|---|
| Automotive outer panels where balance of strength and formability is needed (moderate draws) | Automotive inner parts and cup-shaped components requiring severe or extra-deep drawing |
| Appliance panels and housings where moderate forming and stiffness are needed | Kitchenware, deep-drawn beverage can components (where applicable), complex stamped parts |
| Structural non-safety parts where higher local stiffness or strength is beneficial | Components demanding high surface quality after deep-forming (e.g., decorative interiors) |
| Parts that will be welded and require slightly better post-form strength | High-draw stationery, lampshades, and other items formed in multiple draw operations |
Selection rationale: - Choose SPCE for high drawability, multi-stage forming, and parts where minimizing surface cracking is critical. - Choose SPCD when moderate deep-drawing is needed together with marginally higher strength or when springback control is important.
9. Cost and Availability
- Relative cost: Both grades belong to the same product family and are widely available; cost differences are typically small and driven by processing (anneal cycles, surface control) rather than raw material content. SPCE may carry a small premium because of tighter process controls and higher-quality surface/anneal requirements.
- Availability by form: Cold-rolled coils and sheets in common gauges are broadly available from major mills; specialty widths, tighter surface classes, or extremely low-carbon variants may require longer lead times.
- Procurement tip: Specify required surface class, temper, and mill test certificates rather than only the letter grade to avoid surprises in quoting and supply.
10. Summary and Recommendation
| Characteristic | SPCD | SPCE |
|---|---|---|
| Weldability | Good (requires standard practices) | Very good (generally easier due to lower C) |
| Strength–Toughness | Moderate strength, adequate toughness | Lower strength, excellent ductility |
| Cost | Competitive | Slight premium in some markets for extra-draw processing |
Recommendation: - Choose SPCE if the part requires severe or extra-deep drawing, high uniform elongation, minimal spring-back issues during complex forming, and the highest possible surface formability. SPCE reduces the risk of cracking during aggressive forming operations. - Choose SPCD if you need a balance between drawing performance and higher yield/strength, or if the component requires slightly better control of springback and marginally higher load-bearing in service. SPCD is appropriate for parts with moderate draws where some post-form strengthening or weldability robustness is required.
Final note: The SPC family comprises closely related steels where final performance depends as much on process history (anneal cycle, skin-pass, lubrication, surface class) and supplier practice as on nominal letter grade. For design and procurement use, always require specific mill certificates (chemical analysis and mechanical test results) and, for critical forming or welding operations, perform forming trials or weld procedure qualification with the actual material lot.