Step 1: Set the scene for hot rolling.
Hot rolling is done well above the recrystallisation temperature, so the steel surface is exposed to air at very high heat for an extended time during the process.
Step 2: Think about what happens to a hot metal surface in open air.
Oxygen in the surrounding atmosphere reacts readily with the hot metal surface, and this reaction produces a layer of iron oxide known as scale. This scale is brittle, uneven, and keeps forming as the metal moves through the rolls, so it becomes embedded in the rolled surface.
Step 3: Connect scale formation to the final product quality.
Because of this continuous scaling, the rolled surface comes out rough and often needs a separate cleaning step like pickling before further processing. This is why, unlike the good grain refinement and lower force benefits hot rolling offers, its surface finish is considered a genuine drawback.
\[ \boxed{\text{surface finish is not very good}} \]