In metalworking, what is the process that involves heating and air cooling?

The process involving heating and air cooling in metalworking is known as normalizing. Normalizing is a heat treatment process that aims to refine the grain structure of the metal, resulting in improved mechanical properties, including better strength and toughness. During this process, the metal is heated to a temperature above its critical range, held at that temperature for a specified time to allow for uniform heating, and then air-cooled, which helps to achieve a more uniform microstructure.

This method is particularly beneficial in steel production as it can help eliminate any internal stresses that may have developed during fabrication processes and results in a more consistent material. The air-cooling stage is essential because it helps the metal to return to a more stable phase, enhancing its ductility and strength.

The other options represent different heat treatment processes. For instance, tempering is performed after hardening to reduce brittleness, aging can refer to natural or artificial aging which develops precipitates to strengthen certain alloys, and quenching involves rapid cooling, typically in water or oil, to harden the metal. Understanding the differences between these processes is important in selecting the appropriate method for desired material properties.