Hot Rolling Explained: How HR Coils Are Manufactured
The hot rolling process that turns continuously cast steel slabs into the structural backbone of pipe mills, fabricators and shipyards.
Hot Rolled (HR) Coils are produced by rolling steel above its recrystallization temperature — typically 1100–1250 °C. At that heat the steel is plastic, can be reduced dramatically without cracking, and continually re-forms its grain structure for a tough, formable end product.
1. Continuous Casting of Slabs
Liquid steel from the BOF or EAF is continuously cast into slabs typically 200–250 mm thick, 900–2100 mm wide. Slabs are inspected, scarfed if needed, and stacked for the rolling mill.
2. Reheating Furnace
Slabs are reheated to 1200–1250 °C in walking-beam furnaces under controlled atmosphere. Uniform soak temperature is essential for consistent thickness and mechanical properties down the strip.
3. Roughing Mill
Two-high or four-high reversing roughing stands reduce the slab from ~230 mm down to a transfer bar of 30–40 mm, while edgers control width. High-pressure water descalers blast off iron-oxide scale between passes.
4. Finishing Mill
A six- or seven-stand tandem finishing mill rolls the transfer bar continuously down to final gauge — typically 1.2–25 mm. Each stand contributes a thickness reduction; AGC (automatic gauge control) and bending/shifting systems hold profile and crown within tight tolerances.
5. Run-Out Table & Laminar Cooling
The hot strip travels along the run-out table where banks of water sprays cool it to the coiling temperature — anywhere from 550 °C to 700 °C depending on grade. Cooling rate is the primary lever for setting yield strength and microstructure (ferrite-pearlite, bainite, etc.).
6. Down-Coiler & Finishing
The strip is wound onto a downcoiler producing HR coils of 5–25 MT. Coils are weighed, sampled for chemistry and tensile testing, and tagged with full traceability. Coils destined for cold rolling or galvanizing then go through pickling and oiling (P&O) to remove the mill scale.
Hot Rolled Coils (HR Coils)
Hot rolled coils for heavy structural and pipe manufacturing.
