Hot rolling versus cold rolling achieves which of the following?

Hot rolling versus cold rolling involves distinct processes and outcomes, and the correct answer highlights a typical characteristic of hot rolling.

Hot rolling is conducted at temperatures above the recrystallization temperature of the metal being processed, typically resulting in a final product that may develop a black oxide layer due to oxidation during the heating process. This layer forms because the material is exposed to high temperatures and oxygen in the air, leading to the formation of metal oxides on the surface. The oxide layer can sometimes be advantageous, as it might provide a certain level of corrosion resistance or can be removed in further processing.

In the context of the other options, hot rolling does not necessarily produce a hard final product; rather, it can produce a more ductile and workable material. Cold rolling, on the other hand, tends to increase the hardness of the material through strain hardening due to deformation at lower temperatures. As for cold rolling requiring less machinery, generally, the machinery might not be less complex, and it specifically involves different rollers and processes suited for the conditions of the metal being worked. Cold rolling is performed below the recrystallization temperature, which is opposite to what is stated in the last option, clarifying that the process specifics and conditions are key to understanding the difference between