When chromium is added to alloy steel, it:

Adding chromium to alloy steel primarily increases hardness. Chromium is an alloying element that enhances the strength and toughness of steel. When it's incorporated into the steel's microstructure, it forms hard carbide compounds which contribute to increased wear resistance and overall hardness.

The addition of chromium helps to refine the grain structure, making the steel harder and more durable, especially under high stress or extreme temperatures. This characteristic is particularly valuable in applications where the steel is subject to wear or high temperatures, such as in refrigeration components where durability is essential.

While chromium does have effects on other properties, such as improving oxidation resistance and enhancing some aspects of toughness, its most notable impact is on hardness, which is fundamental in many engineering applications.