What effect is achieved by adding chromium to alloy steel?

Adding chromium to alloy steel primarily enhances hardness, which is why the answer is focused on this aspect. Chromium is a critical alloying element that contributes greatly to the strength and wear resistance of steel. When chromium is added, it helps to form hard carbides within the steel matrix, which ultimately leads to improved hardness and high-temperature strength. This is particularly useful in applications where the steel will be subjected to wear and stress, as the added chromium contributes to the overall performance of the steel under those conditions.

In contrast, while chromium can have some influence on other properties, increased ductility, malleability, and thermal conductivity are not the primary effects attributed to its addition. Ductility and malleability are more closely linked to different alloying elements and the overall composition of the steel, while thermal conductivity is not significantly enhanced by the presence of chromium.