退火 (tuì huǒ) is a heat treatment process used to alter the physical and sometimes chemical properties of a material, typically metals and glass. The process involves heating the material to a specific temperature and then allowing it to cool slowly. This helps to relieve internal stresses, improve ductility, and enhance the material's overall structure. In metallurgy, 退火 is crucial for improving the workability of metals like 钢 (steel) and 铝 (aluminum). By softening the material, it becomes easier to shape and form, making it essential in manufacturing processes such as 锻造 (forging) and 轧制 (rolling).