Q1: Addition of __________ to steel can not impart it high strength at elevated temperature.

ANS:B - magnesium

The addition of magnesium to steel cannot impart it high strength at elevated temperatures. Magnesium is not typically used as an alloying element in steel for the purpose of increasing strength at elevated temperatures. While magnesium can contribute to certain properties in specific alloy systems, it is not commonly employed for enhancing high-temperature strength in steel. Instead, elements such as nickel, silicon, manganese, and others are more commonly added to steel to improve its strength and performance at elevated temperatures. Magnesium is not a commonly used alloying element in steel, as it is primarily used in aluminum alloys and magnesium alloys. In the context of steel, magnesium is not typically added as an alloying element to impart high strength at elevated temperatures. However, magnesium can have certain effects on steel when present, although they are not primarily related to increasing strength at high temperatures. Here are some effects of magnesium in steel:

1. Deoxidization: In steelmaking, magnesium can be used as a deoxidizer. It reacts with oxygen and forms magnesium oxide, which can be removed from the steel melt. This helps in improving the cleanliness of the steel by reducing the oxygen content, which in turn can improve the mechanical properties of the steel.
2. Grain Refinement: Magnesium can also contribute to grain refinement in steel. When added in small amounts, magnesium can refine the grain structure of steel, leading to finer grain sizes. This refinement can improve mechanical properties such as toughness and fatigue resistance.
3. Sulfur Control: In some cases, magnesium can also be used for controlling sulfur levels in steel. Magnesium reacts with sulfur to form magnesium sulfide, which can be removed from the steel during processing. This helps in reducing the sulfur content of the steel, which is important for improving its machinability and ductility.

While magnesium can have these effects on steel, it is not typically added for the purpose of increasing strength at elevated temperatures. Other alloying elements such as nickel, chromium, molybdenum, and silicon are more commonly used for enhancing high-temperature strength and performance in steel alloys.