SPCC and SPHC are the two foundational flat steel specifications in JIS — one cold-rolled (G3141), one hot-rolled (G3131). They are not simply “thin vs thick” versions of the same material. The manufacturing processes produce fundamentally different surfaces, tolerances, and mechanical property profiles. SPCC arrives clean, tight-tolerance, and ready for precision forming and painting. SPHC arrives with mill scale, wider tolerances, and a guaranteed minimum tensile strength of 270 MPa that SPCC lacks entirely. Choosing between them is not about which is “better” — it is about which process suits the manufacturing operation and which properties the application actually requires.
| Property | SPCC (JIS G3141) | SPHC (JIS G3131) |
|---|---|---|
| Rolling process | Cold rolling (room temp) | Hot rolling (~900–1200°C) |
| Thickness range | 0.25–3.2 mm | 1.2–14.0 mm |
| Min tensile strength | Not specified | 270 MPa |
| Elongation (t ≥ 1.0 mm) | ≥ 34% | ≥ 27% |
| Thickness tolerance | ±0.04–0.12 mm (tight) | ±0.15–0.40 mm (wider) |
| Surface | Clean, smooth (no scale) | Mill scale (black) unless pickled |
| ASTM equivalent | A1008 CS | A1011 CS |
| EN equivalent | EN 10130 DC01 | EN 10111 DD11 |
- The Process Difference and Why It Matters
- Chemical Composition Compared
- Mechanical Properties Compared
- Surface and Tolerance Compared
- Selection by Application Type
- Overlap Zone: 1.2–3.2 mm Thickness
- Common Mistakes
- FAQ
1. The Process Difference and Why It Matters
Hot rolling works steel above its recrystallization temperature — the steel is soft, easily deformable, and the rolling forces required are relatively low. The result is a wide thickness range capability (1.2–14+ mm) and a surface covered in iron oxide scale (mill scale) formed by contact with air at 900°C+.
Cold rolling works steel at room temperature, below the recrystallization temperature. The deformation requires much higher force and work-hardens the steel. After rolling, the sheet is annealed (heated to ~700–900°C in a controlled atmosphere) and then skin-passed to the final temper. The result is tighter thickness control, clean scale-free surface, and a surface that accepts paint and coatings directly.
These process differences cascade into every property difference between SPCC and SPHC:
- Surface: SPHC requires pickling or blast cleaning before painting; SPCC can be painted after simple degreasing
- Tolerance: Cold rolling’s precision control allows ±0.04–0.12 mm; hot rolling’s thermal expansion effects allow only ±0.15–0.40 mm
- Strength specification: SPHC specifies minimum TS of 270 MPa; SPCC specifies no minimum TS — only elongation
- Thickness range: SPCC starts at 0.25 mm; SPHC starts at 1.2 mm. Below 1.2 mm, only SPCC is available. Above 3.2 mm, only SPHC (and structural plate) is available
2. Chemical Composition Compared
| Element | SPCC (JIS G3141) | SPHC (JIS G3131) |
|---|---|---|
| C (max) | 0.15% | 0.15% |
| Mn (max) | 0.60% | 0.60% |
| P (max) | 0.100% | 0.040% |
| S (max) | 0.050% | 0.040% |
The key difference is phosphorus: SPCC allows up to 0.100% P, while SPHC limits P to 0.040%. Higher phosphorus in SPCC embrittles grain boundaries — acceptable for general stampings but a concern for applications with welding, notch sensitivity, or low-temperature service. For structural applications where SPHC-range thickness is needed in thinner gauge, SPCD or SPCE (both with P ≤ 0.030%) may be the answer.
3. Mechanical Properties Compared
| Property | SPCC | SPHC | Implication |
|---|---|---|---|
| Min tensile strength | None | 270 MPa | SPHC provides a strength floor for structural calculations; SPCC does not |
| Typical TS range | 270–390 MPa | 290–400 MPa | Overlapping in practice; not substantially different |
| Elongation (t ≥ 1.0 mm) | ≥ 34% | ≥ 27% | SPCC is specified for higher formability; SPHC has lower requirement |
| Grain size | Fine (controlled by cold-roll + anneal cycle) | Coarser (controlled cooling only) | SPCC has more uniform grain structure |
| Residual stress | Low (annealed after rolling) | Very low (hot-rolled, slow cool) | Neither causes significant distortion during machining at these thicknesses |
4. Surface and Tolerance Compared
| Attribute | SPCC | SPHC |
|---|---|---|
| As-delivered surface | Clean, metallic, ready for paint (after degreasing) | Black mill scale — must be removed before painting, welding, or close-tolerance forming |
| Thickness tolerance (1.6 mm) | ±0.07 mm (JIS G3141 Table) | ±0.15–0.20 mm (JIS G3131 Table) |
| Surface roughness (Ra) | ~0.5–2.0 μm (controlled by skin-pass roll) | ~1.5–5.0 μm (scale impression visible on surface) |
| Flatness | ≤ 5–10 mm/1000 mm (sheet camber) | ≤ 7–15 mm/1000 mm (wider flatness tolerance) |
5. Selection by Application Type
Automotive clips, appliance panels, electronics enclosures, brackets requiring tight-tolerance bends. SPCC’s surface cleanliness and tight thickness tolerance enable consistent forming results. For deep draws, step up to SPCE. Thickness: 0.4–2.3 mm typical for stamped parts.
Machine bases, conveyor frames, steel furniture, general fabrication. SPHC provides the 270 MPa TS floor needed for structural calculations, wider thickness range (up to 14 mm), and lower cost than equivalent SPCC. Specify SPHC-PO (pickled and oiled) if the frame will be painted. Mill scale surface is acceptable for hot-dip galvanized assemblies.
Standard “black steel” for laser-cut structural parts, gussets, flanges. Mill scale is consumed or removed by the cutting process; edges require grinding before welding. For laser-cut parts requiring immediate painting without grinding, specify SPHC-PO.
Both grades are available in this range. Select by: (1) surface — SPCC for paint-ready, SPHC or SPHC-PO for structural; (2) tolerance — SPCC for close-tolerance; (3) cost — SPHC is typically cheaper for equivalent thickness and width; (4) strength guarantee — SPHC if the 270 MPa floor matters.
6. Overlap Zone: 1.2–3.2 mm Thickness
Both SPCC and SPHC are available from 1.2 to 3.2 mm — the practical choice in this zone is driven by four factors:
| Decision Factor | Choose SPCC | Choose SPHC |
|---|---|---|
| Surface condition needed | Clean, paint-ready | Mill scale acceptable or SPHC-PO |
| Thickness tolerance | Tight (±0.07–0.12 mm) | Wide acceptable (±0.15–0.30 mm) |
| Strength guarantee needed | Not required for design | 270 MPa minimum required |
| Cost priority | Surface/tolerance worth premium | Lower cost priority |
| Forming type | Complex stampings, deep draws | Simple bends, laser cut, structural use |
7. Common Mistakes
8. FAQ
Q: Can I substitute SPHC for SPCC in a stamping?
For simple bends and flat brackets in the 1.2–3.2 mm overlap range, yes — with SPHC-PO surface and awareness that the wider thickness tolerance may affect fit. For complex stampings, draw depths over 30 mm, or applications requiring consistent paint adhesion, SPCC is necessary. SPHC’s coarser grain structure and mill scale surface are incompatible with precision stamping dies and direct painting.
Q: Is SPHC stronger than SPCC?
SPHC specifies a minimum tensile strength (270 MPa); SPCC does not. In practice, both arrive in the 270–400 MPa range — they are similar in strength. SPHC is not selected for higher strength; it is selected for the thickness range (above 3.2 mm), lower cost, and structural strength guarantee. For significantly higher strength in flat sheet form, specify high-strength hot-rolled steel (e.g., JIS G3134 SAPH440/SAPH590 for automotive structural use).
Summary
- SPCC (cold-rolled): 0.25–3.2 mm, clean surface, tight tolerance, no minimum TS — for precision stampings and painted parts
- SPHC (hot-rolled): 1.2–14.0 mm, mill scale surface, wider tolerance, 270 MPa min TS — for structural fabrication, laser cut stock, welded frames
- In the 1.2–3.2 mm overlap zone: choose based on surface (clean vs scale), tolerance need, and whether the 270 MPa TS floor matters
- SPHC is cheaper than SPCC in the overlap zone — but the thickness tolerance difference can create hidden rework costs in precision assemblies
- Specify SPHC-PO (pickled and oiled) when SPHC will be directly painted or welded in clean condition
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