Short answers, pulled from the story.
Rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce thickness, make thickness uniform, and impart desired mechanical properties. The gap between the rolls is smaller than the incoming material, causing it to deform and elongate. Friction at the roll-material interface draws the metal through.
Hot rolling takes place above the metal's recrystallization temperature, allowing grains to recrystallize during processing and preventing work hardening. Cold rolling takes place below the recrystallization temperature, which increases strength through strain hardening by up to 20 percent and produces tighter tolerances and a better surface finish. Hot rolling handles more total tonnage than any other manufacturing process, while cold rolling leads all cold working processes.
Henry Cort of Funtley Iron Mills, near Fareham in Hampshire, England, is called the father of modern rolling by modern writers. In 1783, he received a patent for using grooved rolls to roll iron bars, a design that enabled mills to produce fifteen times more output per day than a hammer. Although he was not the first to use grooved rolls, he was the first to combine the best features of many known ironmaking and shaping processes.
The earliest rolling mills, called slitting mills, were introduced from what is now Belgium to England in 1590. In 1697, Major John Hanbury erected a mill at Pontypool to roll blackplate. The first recorded use of a steam engine directly driving a rolling mill occurred in 1786 at John Wilkinson's Bradley Works, where a Boulton and Watt engine was coupled to a slitting and rolling mill.
Ring rolling is a specialized form of hot rolling that increases the diameter of a ring by thinning its walls. It produces a circumferential grain structure that gives better mechanical properties. Common applications include railway tyres, bearings, gears, aircraft components, rockets, turbines, pipes, and pressure vessels, with diameters reaching up to 8 meters and face heights up to 2 meters.
Six types of surface defects affect rolled products: laps, mill-shearing, rolled-in scale, scabs, seams, and slivers. Laps form when a corner folds over and is rolled without welding into the metal. Seams result from scale or pass roughness in the roughing mill. Many surface defects can be removed by scarfing before further rolling, using methods ranging from hand chipping with chisels to laser scarfing.