What does polymorphism in metals refer to?

Polymorphism in metals specifically refers to the ability of a metal to exist in more than one crystal structure depending on the temperature and pressure conditions. This characteristic is critical in metallurgy because different crystal structures can lead to varying physical properties, such as deformation characteristics, ductility, and strength.

For instance, iron exhibits polymorphism; at room temperature, it exists in a body-centered cubic (BCC) structure known as alpha-iron, and at higher temperatures, it transforms into a face-centered cubic (FCC) structure called gamma-iron. This transformation influences the metal's behavior in processes such as welding, casting, and heat treatment.

Understanding polymorphism is essential for engineers to manipulate the properties of metals for specific applications by controlling the temperature and other environmental factors during processing. This property is distinct from other options in the list, which focus on conductivity, corrosion resistance, and forgeability, none of which relate to the structural changes in metals due to temperature.