Pig iron is a kind of iron alloy with high carbon content and high toughness, but it is also easy to rust. Steel is an alloy composed of iron, carbon and other alloying elements, such as chromium and nickel. The properties of steel can be adjusted by controlling carbon content and adding alloying elements. Generally speaking, steel has high strength and hardness, but it may show some brittleness compared with pig iron.
Aluminum is a light and strong metal with good electrical and thermal conductivity. Because of its low density, it is widely used in various fields, such as aerospace, architecture, electronic industry and so on.
Tin paper is a composite material composed of tin and other metals (such as aluminum). Although tin itself is a relatively soft metal, it can provide certain compressive and corrosion resistance when combined with other materials. Tin foil is mainly used for packaging and cooking, but it is really not suitable for cooking, because tin melts easily at high temperature, and some foods may react with tin.
Hardness and hardness are similar but slightly different concepts. Robustness usually refers to the overall stability of a material and its ability to resist deformation or damage. Hardness focuses on the ability of materials to resist external forces, which means that their surfaces are not easy to be cut, compressed or deformed. Although firmness and hardness can be synonymous in some cases, they are not completely consistent, and it is necessary to accurately describe the properties of materials in combination with specific contexts.