During the induction hardening process, which aspect is crucial for achieving a hard surface?

Localized heating with controlled induction is crucial for achieving a hard surface during the induction hardening process. This method allows for the precise application of heat to specific areas of the material, typically the surface, which raises its temperature rapidly. The key aspect of induction hardening is that this localized heating can target only the areas that require hardening, ensuring minimal impact on the core properties of the metal below the surface.

Once the surface reaches the desired austenitizing temperature, it is then rapidly cooled, usually with quenching techniques. This rapid cooling transforms the austenite phase into a harder martensitic phase, resulting in increased hardness and improved wear resistance. Therefore, the combination of controlled heating and rapid cooling is essential for creating a durable hardened surface while maintaining the integrity of the underlying material. The approach used in induction hardening is particularly effective, as it results in a high degree of hardness transformation without the extensive thermal stresses that could occur with prolonged heating or broader area heating.