Stage 1: Heating

Purpose: To increase the slab's plasticity, reduce its deformation resistance, and make it suitable for rolling.

Equipment: Typically a Walking Beam Furnace.

Process:

1. Slabs (typically 150-250mm thick) from the continuous caster are charged into the furnace.

2. They are heated slowly and uniformly according to a preset curve to 1100°C – 1250°C (depending on steel grade) to achieve complete austenitization and uniform temperature throughout.

Stage 2: Rolling

This is the core stage, divided into Roughing and Finishing.

Descaling:

• After exiting the furnace, the red-hot slab first passes through a High-Pressure Water Descale Box.

• Water jets at pressures above 200 bar remove the primary scale formed during heating, ensuring final surface quality.

Roughing Mill:

• Purpose: To reduce the slab thickness with large reductions, producing a Transfer Bar (typically 30-50mm thick).

• Equipment: A reversing mill or a continuous roughing mill train.

• Characteristic: Few passes with high reduction per pass, minimal temperature loss.

Finishing Mill:

• Purpose: To roll the transfer bar down to its final target thickness (typically 1.2mm – 25.4mm) while controlling dimensional accuracy, shape (flatness), and surface quality.

• Equipment: A tandem mill consisting of 6-7 four-high mill stands.

• Process: The transfer bar passes continuously at high speed (up to 20+ m/s) through each stand. Each stand applies a small reduction. AGC (Automatic Gauge Control) and Shape Control systems make real-time adjustments. The final strip exits at the desired thickness.

Stage 3: Cooling & Coiling

Run-Out Table Cooling (Laminar Cooling):

• The strip exiting the finishing mill is still above 800°C. It immediately enters the laminar cooling section.

• Controlled, uniform cooling is applied by hundreds of top and bottom headers using a curtain of water.

• Cooling Rate is a critical parameter that determines the final microstructure and mechanical properties (e.g., grain size, phase composition, strength, toughness).

Downcoiling:

• When the strip front reaches the target coiling temperature (typically 550°C – 650°C), it engages the Downcoiler.

• The downcoiler winds the hundreds-of-meters-long hot strip into a Hot Rolled Coil, weighing tens of tons.

Stage 4: Finishing & Inspection (Customer Dependent)

Cooling: Coils are cooled to room temperature in storage yards (air cooling or forced cooling).

Finishing Operations:

• Skin-Pass/Slight Cold Rolling: Improves flatness, surface finish, and imparts a slight hardening.

• Trimming (head/tail and side trimming).

• Slitting: Cutting the wide coil into multiple narrow strip coils.

• Cut-to-Length/Shearing: Uncoiling, leveling, and shearing the coil into discrete plates/sheets.

Inspection: Final checks on dimensions, surface, and properties (via sample testing).

Packaging & Shipping: Packaged according to customer requirements and dispatched.