The key differences between hot-rolled and cold-rolled steel products lie in the manufacturing process and resulting properties. Hot-rolled steel is produced at high temperatures, resulting in a rougher surface and less precise dimensions. It is generally used in applications where structural strength is important. On the other hand, cold-rolled steel is processed at lower temperatures, resulting in a smoother surface and more precise dimensions. It is often used in applications where aesthetics and tight tolerances are essential, such as automotive panels or appliances.

The global steel industry has a significant impact on the economy as it is a crucial sector that contributes to the growth and development of various industries. Firstly, the steel industry generates substantial employment opportunities, both directly and indirectly, creating jobs in steel production, manufacturing, distribution, and related sectors. This leads to increased incomes and improved living standards for workers and their families. Secondly, the steel industry is a major driver of economic growth and industrialization. Steel is a fundamental material used in construction, infrastructure development, and manufacturing, making it indispensable for various sectors such as automotive, machinery, and energy. The demand for steel directly influences the growth of these industries, stimulating investment, innovation, and technological advancements. Moreover, the steel industry plays a crucial role in international trade. Steel is one of the most traded commodities globally, and its production and export contribute to a country's trade balance. Countries with a strong steel industry can leverage their competitive advantage, earning foreign exchange and enhancing their economic competitiveness. However, it's important to note that the global steel industry also faces challenges such as overcapacity, price fluctuations, and environmental concerns. These factors can impact the economy by affecting profitability, trade balances, and sustainability efforts. Thus, governments and industry stakeholders must work together to address these challenges and ensure a balanced and sustainable growth of the global steel industry.

Steel is commonly used in the construction of bridges due to its high strength and durability. It is used to create the main load-bearing elements, such as beams and girders, which provide structural support and distribute the weight of the bridge. Steel is also used for the construction of bridge decks, which are the surfaces that vehicles and pedestrians travel on. Additionally, steel is often used for the construction of bridge cables, which help to suspend and stabilize the bridge. Overall, steel's versatility and strength make it a vital material in bridge construction.