Chromium increases a material's resistance to corrosion and oxidation, as well as strength under high temperatures, hardenability, and wear resistance.

• A. Chromium decreases ductility
• B. Chromium increases corrosion and oxidation resistance, strength at high temperatures, hardenability, and wear resistance
• C. Chromium lowers melting point
• D. Chromium reduces wear resistance

Answer: (B)

Chromium contributes to multiple protective and strengthening mechanisms in alloy steels. It forms a stable chromium oxide film on the surface that passivates the metal, greatly boosting resistance to corrosion and oxidation, especially in stainless steels. It also strengthens the material at high temperatures through solid-solution strengthening and by forming hard second-phase particles such as carbides, which helps maintain strength when things get hot.

In addition, chromium slows diffusion during heat treatment, which increases hardenability—the ability to achieve a hard, tempered microstructure deeper inside the piece. This combination of surface protection, retained high-temperature strength, and improved hardenability translates into better wear resistance as well, since harder, more wear‑resistant phases are formed and maintained.

Other statements don’t fit as well: chromium does not typically lower melting point and, in general, does not reduce wear resistance; and while ductility can be affected by composition, the overall properties described—corrosion/oxidation resistance, high-temperature strength, hardenability, and wear resistance—are the defining, well-supported effects of adding chromium.