Hot-rolled coils, formally known as hot-rolled steel plate coils, refer to steel products manufactured from steel billets. These are continuously rolled through rolling mills at high temperatures until they attain specified thicknesses and widths, ultimately supplied in coiled form. It stands as one of the most extensively produced and widely applied fundamental steel products within the iron and steel industry, serving as the core ‘parent material’ for downstream steel products such as cold-rolled coils and galvanised coils.

I. Core Production Process: Key Steps in High-Temperature Rolling

Hot-rolled coil production relies on continuous, high-precision rolling mills. The core process involves softening steel at elevated temperatures to achieve plastic deformation and control final dimensions. The sequence comprises three principal stages:

Heating Stage

Room-temperature continuous cast billets (typically 150mm × 150mm to 250mm × 250mm in cross-section, 6-12m in length) into a step-heating furnace. Within an oxygen-free environment, the billet is heated to 1100-1250°C (varying by steel grade) to uniformly soften its internal structure and impart favourable plasticity, preparing it for subsequent rolling.

This stage requires strict control of heating rates and soak times to prevent excessive surface oxidation (forming overly thick scale) or internal cracking.

Rolling Stage (Core Process)

Rough Rolling: The high-temperature billet first enters the roughing mill (typically comprising 4–6 stands). Through multiple passes, the billet thickness is reduced from 150–250 mm to 10–30 mm intermediate billets, whilst the width is preliminarily adjusted (controlled via the stand rollers).

Finish Rolling: After surface scale is removed via high-pressure water in the descaler, the blooms enter the finishing mill (usually comprising 6-7 continuous rolling stands). Under high-precision control (thickness tolerance within ±0.1mm), they are progressively rolled to the target plate thickness (typically 1.2-20mm, with some thin grades reaching 0.8mm).

During rolling, the steel plate temperature must be synchronously controlled (final rolling temperature typically 800-950°C) to ensure uniform mechanical properties.

Cooling and Coiling Stage

Laminar cooling: Post-finishing, the high-temperature steel plate (approximately 800°C or above) enters the laminar cooling system. Through upper and lower spray cooling water, it is rapidly and uniformly cooled to 550-650°C (the ‘coiling temperature’). This stage directly influences the steel's grain size and properties such as hardness and strength.

Coiling: The cooled steel plates are wound by a coiler into coils with diameters of 1.2–2.0 metres. These coils are then strapped, labelled (indicating steel grade, specifications, weight, production date, etc.), and stored in the warehouse.