What is the main purpose of hardening steel?

The main purpose of hardening steel is to increase its hardness by forming martensite. This process involves heating the steel to a high temperature, allowing the carbon and iron to dissolve into a solid solution, and then rapidly cooling it, typically in water or oil. This rapid cooling transforms the steel's microstructure into martensite, which is a much harder and stronger phase compared to its initial structure.

This increase in hardness is particularly valuable in applications where steel is subjected to wear, abrasion, or impact, as it helps the steel maintain its integrity and performance under stress. Martensitic steel is, therefore, essential in tools, machinery, and structural components that require enhanced strength and durability.

In contrast, reducing the weight of the metal, increasing ductility and toughness, or improving corrosion resistance are not primary objectives of the hardening process. While these attributes can be important in the overall design and performance of steel components, they do not directly relate to the fundamental purpose of hardening to achieve higher hardness through martensitic transformation.