Steel: Bones of Civilization — Casting Slabs, Billets & Beams
We pour sunlight into shapes. Yesterday’s coal furnaces have been swapped for clean arcs; today we turn liquid light‑metal into the bones of bridges, rails, towers, and tools — quietly, precisely, and at speed.
Why steel (and why now)
Steel is still civilization’s strongest poetry per kilogram. The trick was never the metal — it was the smoke. With clean power (Part 3–4) and smart sorting (Part 2), we cast and roll at world scale without coughing at the sky.
- Demand is huge: towers, rails, ships, factories, solar frames, wind towers.
- Electrified process: EAFs and electric reheat make mills grid‑friendly neighbors.
- Direct rolling: hot metal into the mill = less energy, less time, less drama.
Casting 101 (slabs, blooms, billets)
Continuous casting (CCM)
Liquid steel flows into water‑cooled molds, skin freezes, strand is pulled and cut. No giant ingot parks, no reheating museums — just a steady river of steel.
Slab: 200–250 mm thick • up to 2,000 mm wide Bloom: 200–350 mm square Billet: 100–180 mm squareCasting speed: slab ~1–2 m/min; billet ~3–6 m/min (grade dependent).
Energy & yields at the caster
- Caster electricity: ~20–40 kWh/t (drives, secondary cooling)
- Yield melt→cast: ~92–96% (trimming, tundish, head/tail)
- Hot charging: direct to mill at 700–1000 °C cuts reheating by 60–90%
Electric reheat, not flames (why this matters)
Heat the steel, not the air
We use induction and resistance furnaces for slabs, blooms, and billets. They couple energy directly into metal; nothing goes up a stack.
- Full reheat (cold slab → 1,200 °C): ~0.25–0.35 MWh/t
- Hot charge (700–900 °C → 1,200 °C): ~0.05–0.15 MWh/t
- Rolling drives & auxiliaries: ~0.08–0.15 MWh/t
Numbers include recuperation and modern motor systems; design for the high end, celebrate the low.
Why mills love the microgrid
- Predictable duty cycles → easy for storage to cover peaks.
- Heat recovery → process steam for neighbors (paint, laundry, food).
- No NOx burners → clean air and fewer permits.
Rolling lines & products (what we make)
Hot Strip Mill (HSM) — coils
Slabs become coil for cars, appliances, ship plate precursors, and solar trackers.
- Entry: 200–250 mm slab
- Exit: 1.2–20 mm strip
- Line power (elec): ~0.12–0.25 MWh/t (with hot charge)
Plate / Steckel — heavy plate
Thick, wide plate for wind towers, bridges, ship hulls.
- Exit: 10–150 mm plate
- Line power: ~0.10–0.20 MWh/t (hot charge)
Section / Rod — beams, rails, rebar, wire
Billets/blooms become rebar, H‑beams, rails, wire rod.
- Line power: ~0.08–0.18 MWh/t (hot charge)
- Rails: straightness <0.3 mm/m
Per‑ton cheat sheet (steel products)
Electricity (beyond melting)
| Operation | kWh per ton | Notes |
|---|---|---|
| Caster & cut‑to‑length | 20–40 | Drives, water |
| Reheat (cold slab) | 250–350 | Induction/resistance |
| Reheat (hot charge) | 50–150 | Depends on entry temp |
| Rolling & aux | 80–150 | Motors, hydraulics |
Total (hot‑charged coil): ~0.20–0.40 MWh/t. Total (cold slab): ~0.35–0.50 MWh/t.
Yields (melt → final)
| Step | Yield % | Comment |
|---|---|---|
| EAF tap → caster | 92–96% | Trims, tundish |
| Caster → mill | 97–99% | Cut ends |
| Mill → product | 95–98% | Edge trim, scrap |
Overall: ~85–92% depending on product mix and hot charging. Scrap loops back to EAF.
Pre‑calculated plant scenarios
Scenario A — Mini‑mill (long products, scrap→EAF)
Capacity 1 Mt/yr • billets/blooms → rebar, H‑beams, rails.
| Item | Value |
|---|---|
| Avg throughput | ~125 t/h (8,000 h/yr) |
| EAF electricity (melt) | ~0.50 MWh/t → ~62.5 MW |
| Caster + rolling (hot charge) | ~0.15 MWh/t → ~18.8 MW |
| Total avg load | ~80–90 MW |
| PV min (to cover daily) | ~410–460 MWp |
| Storage (12 h) | ~0.96–1.08 GWh |
| Footprint | ~20–35 ha (mills + yards) |
PV min sized by Avg(MW)×5.14 (5.5 PSH, 85% DC→AC). We oversize to power neighbors.
Scenario B — Flat products hub (DRI(H₂)+EAF + HSM)
Capacity 5 Mt/yr • slabs → coils/plate with extensive hot charging.
| Item | Value |
|---|---|
| Avg throughput | ~625 t/h |
| DRI(H₂)+EAF electricity | ~3.5–4.0 MWh/t → ~2.2–2.5 GW |
| Rolling (hot charge) | ~0.20 MWh/t → ~125 MW |
| Total avg load | ~2.3–2.6 GW |
| H₂ consumption | ~250–300 kt/yr |
| PV min | ~12–13 GWp |
| Storage (12 h) | ~28–31 GWh |
| Footprint | ~60–120 ha + PV field nearby |
Electrolyzers dominate power. Rolling is the polite part.
Product mix dial (1 Mt/yr plant)
| Mix | Coil | Plate | Sections/Rod | Avg elec (MW) |
|---|---|---|---|---|
| Coil‑heavy | 60% | 10% | 30% | ~86 |
| Balanced | 40% | 20% | 40% | ~82 |
| Long‑heavy | 20% | 10% | 70% | ~79 |
Differences come from rolling motor demand and reheating fractions; EAF load is similar.
Yields, quality & zero‑waste loops
Scrap is a feature, not a bug
- Edge trim, cobbles, and off‑cuts go straight to the EAF bucket.
- On‑site shred & preheat cut melt energy and tap‑to‑tap time.
- Billet/coil ends feed a small foundry for castings and machine shop stock.
QA the fun way
- Inline gauges: thickness, profile, flatness.
- Metallurgy on rails: spectrometers at caster; hardness and grain at downcoilers.
- Traceability: every beam and coil carries a digital birth certificate.
Footprint & staffing (1 Mt/yr mini‑mill)
Area
- Melt shop + caster: ~8–12 ha (enclosed)
- Rolling & finishing: ~8–15 ha
- Yards & logistics: ~5–8 ha
- PV field (min): ~2.0–2.5 km² (nearby)
People & skills
- Operations crews per bay (3 shifts), strong automation backbone.
- Electricians > burner techs (by design).
- Metallurgists, quality, maintenance, and a lemonade stand for visiting school trips.
Q&A
“Do beams and coils really come from the same melt?”
Yes — slabs for coil/plate and billets/blooms for sections/rod drop from parallel caster strands. Same chemistry, different shapes, same lack of smoke.
“What about galvanizing and coating?”
Next door. Electric anneal lines, zinc/aluminum baths, and coil coaters live on the same microgrid, sipping surplus solar from Part 3.
“Can we hot‑charge everything?”
Almost. Smart buffers keep strand temperature high into the mill; when we must pause, electric reheat fills the gap without firing dragons.
Up next: Aluminum, Copper & Rare Metals — Veins of Power (Part 6). Wires, light alloys, and battery metals — the nervous system to our bones.