Which material increases hardness when added to alloy steel?

The material that increases hardness when added to alloy steel is chromium. This is largely due to the fact that chromium enhances the strength, hardness, and wear resistance of steel. When chromium is added in appropriate amounts, it helps to form carbides and effectively stabilizes the microstructure of the steel, resulting in improved hardness.

Chromium also promotes the formation of tough, wear-resistant phases in the steel matrix, which contributes to its overall mechanical properties. This is particularly important in applications where high hardness and resistance to abrasion are required, such as in tools and high-performance machinery parts.

In contrast, while iron is the primary component of steel and can impact its properties, it does not inherently increase hardness in the same way as chromium. Aluminum does not significantly increase hardness in alloy steel; rather, it serves to improve other properties, such as corrosion resistance. Chrome, while often referring to chromium, does not independently convey the same property enhancements as chromium in the context of alloying to improve hardness.