Which process involves introducing both carbon and nitrogen to increase hardness?

The process that involves introducing both carbon and nitrogen to increase the hardness of steel is carbonitriding. This method combines elements of both carburizing and nitriding. During carbonitriding, steel is exposed to a carbon and nitrogen-rich environment, typically at elevated temperatures. The carbon adds hardness through the formation of hard microstructure phases, while nitrogen enhances surface hardness by forming nitrides, which improve wear resistance and fatigue strength.

This dual treatment is beneficial because it not only enhances the hardness of the surface but can also improve the material's toughness. The process typically occurs in a controlled atmosphere and can be used to harden low-carbon steels, making it a suitable choice for applications where both hardness and toughness are necessary.

In contrast, nitriding primarily focuses on nitrogen to increase hardness, while carburizing relies solely on carbon. Quenching, on the other hand, is a heat treatment process that hardens metal but does not introduce additional elements like carbon or nitrogen.