Steel doors are primarily made of steel, which is an alloy of iron and carbon. The main components of a steel door include:

1. Steel sheets or panels: Steel doors are constructed from steel sheets or panels, which can be galvanized or coated with protective layers to enhance their corrosion resistance. These steel sheets form the outer layers of the door, providing strength and durability.
2. Insulating core: To improve thermal and acoustic insulation, the space between the steel sheets is typically filled with an insulating material, such as polyurethane foam or mineral wool. This insulation helps to maintain indoor temperatures and reduce energy consumption, as well as dampen outside noise.
3. Reinforcements: Steel doors often have additional reinforcements, such as vertical and horizontal stiffeners or channels, to increase their structural rigidity and resistance to forced entry or break-ins.
4. Hardware components: Steel doors are equipped with various hardware components, such as hinges, locks, handles, and other accessories. These components are typically made from metal materials, like brass, stainless steel, or aluminum, to ensure durability and long-lasting performance.
5. Surface treatment and finish: The steel door’s surface is often treated and finished to improve its appearance and corrosion resistance. This can include processes such as degreasing, pickling, phosphating, priming, painting, or powder coating.

In summary, steel doors are primarily made of steel sheets or panels, with an insulating core and additional reinforcements. Hardware components and surface treatments complete the door, ensuring durability, security, and an aesthetically pleasing appearance.