What is the process of adding carbon to the surface of steel to enhance its hardness?

The process of adding carbon to the surface of steel to enhance its hardness is known as pack carburizing. This method involves heating steel in a carbon-rich environment, which allows carbon to diffuse into the surface of the steel. As the carbon concentration increases near the surface, it imparts greater hardness and improves the wear resistance of the steel.

Pack carburizing specifically uses a pack of carbon-rich materials, such as charcoal or other carbon-containing substances, which are placed around the steel part in a sealed container and heated. The temperature and duration of this process can be controlled to achieve the desired depth of carbon penetration and hardness.

While case hardening is a correct term that refers to surface hardening techniques in general, pack carburizing is a specific method within that category. Nitrocarburizing involves the introduction of nitrogen along with carbon to improve surface hardness but is distinct from traditional carburizing. Tempering, on the other hand, is a heat treatment process used after hardening to relieve stress and reduce brittleness but does not add carbon to the surface.