Which characteristic does the process of case hardening primarily improve in steel?

The process of case hardening primarily improves the wear resistance of steel. Case hardening involves hardening the surface layer of a material while allowing the core to retain its toughness and ductility. This is achieved through processes such as carburizing, nitriding, or carbonitriding, which introduce carbon or nitrogen into the surface layer of the steel.

The hard outer layer greatly enhances the material's ability to withstand abrasion, impact, and surface wear, which is crucial for parts like gears, axles, and bearings that experience high levels of friction and contact with other materials. The tough core allows these parts to absorb shock without fracturing, making the overall combination effective for performance under demanding conditions.

While it could be thought that case hardening might affect toughness, corrosion resistance, or electrical conductivity, these characteristics are not the primary focus of the case hardening process. Toughness, which refers to a material's ability to absorb energy and deform without fracturing, is maintained in the core and not improved by the hardening of the surface alone. Corrosion resistance is more influenced by coatings or alloy compositions rather than case hardening. Electrical conductivity is also not related, as hardening focuses on mechanical properties rather than electrical properties.