SPHC is the JIS G3131 designation for general-purpose hot-rolled steel sheet — the heavy-gauge counterpart to SPCC. Where SPCC starts at 0.25 mm and runs to 3.2 mm, SPHC covers 1.2 mm to 14.0 mm and is the standard specification for thick stampings, structural blanks, brackets, and hot-rolled base material for downstream processing (pickling, cold rolling, galvanizing). SPHC differs from SPCC in two important ways: it carries a minimum tensile strength of 270 MPa, and its surface is covered in mill scale unless specifically ordered as pickled. Understanding when to specify SPHC over SPCC — and when the mill scale matters — saves specification errors and procurement delays.
| Property | SPHC (JIS G3131) |
|---|---|
| Standard | JIS G3131:2018 |
| Form | Hot-rolled sheet and strip, 1.2–14.0 mm thickness |
| ASTM equivalent | A1011 CS (Commercial Steel) |
| EN equivalent | EN 10111 DD11 |
| Minimum tensile strength | 270 MPa |
| Elongation (t ≥ 2.0 mm) | ≥ 27% |
| Surface | Mill scale (black) as standard; pickled (PO) optional |
| Carbon (max) | 0.15% |
- Hot Rolling vs Cold Rolling — What It Means for the Material
- Chemical Composition
- Mechanical Properties
- Grade Designations Within JIS G3131
- Mill Scale and Surface Conditions
- ASTM and EN Equivalents
- Common Mistakes
- Applications
- FAQ
1. Hot Rolling vs Cold Rolling — What It Means for the Material
Hot rolling is performed above the steel’s recrystallization temperature (~900–1200°C). At these temperatures, the steel is soft enough to roll to thickness without requiring the large rolling forces needed for cold work. The consequences for the finished sheet:
- Thickness range: Hot rolling can achieve 1.2–14.0 mm economically; cold rolling typically handles 0.25–3.2 mm
- Surface: Contact with air above 570°C forms iron oxide scale (mill scale — a mixed Fe₂O₃/Fe₃O₄/FeO layer). This scale is hard, brittle, and must be removed (pickling) before painting, welding, or cold forming
- Dimensional tolerance: Hot-rolled tolerances are wider than cold-rolled — typically ±0.15–0.40 mm on thickness versus ±0.04–0.12 mm for cold-rolled
- Residual stress: Hot rolling produces lower residual stress than cold rolling; hot-rolled plate is less prone to warping during machining than cold-rolled
- Strength: Hot-rolled material is softer and more ductile than equivalent cold-rolled (no work hardening); minimum TS is only 270 MPa for SPHC versus typical 280–380 MPa for SPCC
2. Chemical Composition
| Element | SPHC | SPHD | SPHE |
|---|---|---|---|
| C (max) | 0.15% | 0.10% | 0.08% |
| Mn (max) | 0.60% | 0.50% | 0.45% |
| P (max) | 0.040% | 0.035% | 0.030% |
| S (max) | 0.040% | 0.035% | 0.030% |
Source: JIS G3131:2018. Note that SPHC has tighter phosphorus limits (0.040%) than SPCC (0.100%) — the hot-rolling process and the applications (thicker structural parts) demand cleaner steel. SPHD and SPHE parallel SPCD and SPCE in the cold-rolled family: progressively lower C, Mn, P, and S for deeper hot draws.
3. Mechanical Properties
| Property | SPHC | SPHD | SPHE |
|---|---|---|---|
| Tensile strength (min) | 270 MPa | 270 MPa | 270 MPa |
| Elongation (t < 2.0 mm) | ≥ 25% | ≥ 29% | ≥ 31% |
| Elongation (t ≥ 2.0 mm) | ≥ 27% | ≥ 31% | ≥ 33% |
| r-value (Lankford) | Not specified | Not specified | ≥ 1.4 (for t ≥ 1.6 mm) |
The 270 MPa minimum tensile strength is a key distinction from SPCC. SPHC is intended for applications where a structural minimum is needed — heavy brackets, reinforcing sections, structural stampings — where SPCC’s unspecified tensile strength would be insufficient for design calculations. In practice, SPHC typically arrives at 290–400 MPa tensile strength.
4. Grade Designations Within JIS G3131
| Grade | Formability | Minimum TS | Use Case |
|---|---|---|---|
| SPHC | General | 270 MPa | Structural blanks, heavy brackets, base plate, laser-cut parts |
| SPHD | Drawing | 270 MPa | Hot-drawn shells, thicker automotive stampings |
| SPHE | Deep drawing | 270 MPa | Deep-drawn thick-wall parts: tanks, pressure housings |
5. Mill Scale and Surface Conditions
Mill scale is the defining characteristic of hot-rolled steel. The scale layer (20–100 μm thick) consists of:
- Outer layer: Fe₂O₃ (hematite, red-brown, hard)
- Middle layer: Fe₃O₄ (magnetite, blue-black, very hard)
- Inner layer: FeO (wüstite, unstable below 570°C, breaks down on cooling)
Mill scale must be removed before:
- Painting or powder coating: Scale has poor adhesion to the steel substrate and will delaminate under the paint film
- Welding: Scale in the weld zone creates porosity and inclusions; grind the weld area clean first
- Cold forming (bending, drawing): Scale abrades tooling and embeds in the steel surface; pickled-and-oiled (PO) material is required for formed parts with tight tolerances
- Electroplating or galvanizing (electro): Acidic pre-treatment removes scale automatically, but excessive scale load slows the line
| Surface Condition Code | Meaning | Use When |
|---|---|---|
| (no suffix) | As-rolled, mill scale present | Structural use, hot-dip galvanizing, laser cutting with scale removal |
| -PO (Pickled and Oiled) | Acid-pickled to remove scale, then oiled to prevent re-oxidation | Forming, painting, welding in clean condition |
| -P (Pickled, no oil) | Pickled but not oiled | Immediate processing only; surface rusts quickly |
6. ASTM and EN Equivalents
| JIS G3131 | ASTM A1011 | EN 10111 | Notes |
|---|---|---|---|
| SPHC | CS Type B | DD11 | Similar composition and TS minimum |
| SPHD | DS Type B | DD12 | Drawing quality |
| SPHE | DDS | DD13 | Deep drawing quality |
ASTM A1011 and JIS G3131 are close but not identical: A1011 CS specifies a maximum yield-to-tensile ratio (≤ 0.80) and a slightly different elongation measurement method. For direct substitution in structural applications, confirm the yield strength range from the mill certificate — SPHC and A1011 CS overlap significantly in practice but are not formally interchangeable without qualification.
7. Common Mistakes
8. Applications
Machine bases, welded frames, structural brackets, sub-frames. SPHC’s 270 MPa minimum TS and tighter P limit (vs SPCC) make it the standard choice for load-bearing fabrications where strength matters.
Standard “black steel” plate for laser and plasma cut parts. The mill scale is typically acceptable for cut parts that will be machined, welded, or hot-dip galvanized downstream. SPHC-PO is used when cut parts need immediate painting.
Hot-rolled coil (SPHC equivalent) is the feedstock for cold-rolling mills (which produce SPCC), galvanizing lines (SGCC substrate), and pipe welding mills. Much of SPHC produced never reaches the end user as SPHC — it is further processed.
9. FAQ
Q: Can I substitute SPHC for SPCC in a stamping application?
Only for simple bends and flat blanks — not for deep draws. SPHC has coarser grain structure, wider thickness tolerance, and mill scale surface compared to SPCC. For complex stampings, stick with cold-rolled grades. For heavy-gauge simple stampings (above 3.0 mm where SPCC is not available), SPHC-PO is the practical choice.
Q: What is the difference between SPHC and SS400 in plate form?
SPHC (JIS G3131) and SS400 (JIS G3101) overlap in application but serve different purposes. SS400 specifies minimum TS of 400 MPa — significantly higher than SPHC’s 270 MPa. SPHC is a formability-focused grade; SS400 is a strength-focused structural grade. For welded frames where strength governs, SS400 is standard. For fabricated components where formability and cost govern, SPHC is used.
Summary
- SPHC (JIS G3131) — general-purpose hot-rolled steel sheet; minimum TS 270 MPa; thickness 1.2–14.0 mm
- ASTM A1011 CS Type B / EN 10111 DD11 — functional equivalents
- Mill scale is standard surface condition — specify -PO (pickled and oiled) for forming, welding in clean condition, or painting
- SPHC → SPHD → SPHE: progressively better formability (parallels SPCC/SPCD/SPCE in cold-rolled family)
- Use SPHC for heavy structural stampings, laser-cut blanks, and welded frames; use SPCC for thin-gauge, tight-tolerance, or precision-stamped parts
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