Correct Answer: C. Increases
Solution:
Chromium is a key alloying element in steel. It is a strong carbide former, which significantly increases the steel's hardness, hardenability, and wear resistance. This increase in hardness directly contributes to a higher tensile strength.
Correct Answer: D. Toughness
Solution:
Shock resistance is the ability of a material to absorb energy and withstand sudden impacts without fracturing. This property is known as toughness. Shock-resisting steels are specifically designed to have high toughness.
Correct Answer: A. Along the lines of slag distribution
Solution:
The manufacturing process of wrought iron creates a fibrous structure where slag impurities are drawn into long filaments, similar to the grain in wood. The material is strongest when pulled parallel to these fibers, i.e., along the lines of slag distribution.
Correct Answer: D. Chrome steel
Solution:
Ball bearings require extremely high hardness, wear resistance, and compressive strength to function. Chrome steel (a type of high-carbon steel alloyed with chromium) is the standard material used because it can be hardened to a very high degree and has excellent resistance to wear and fatigue.
Correct Answer: C. Bosh
Solution:
The widest part of a blast furnace is called the belly. The section immediately below this, which slopes inwards towards the bottom, is known as the bosh. This is where the highest temperatures are reached and combustion is most intense.
Correct Answer: B. Mild steel
Solution:
Of the options given, mild steel is the most susceptible to corrosion (rusting) in the presence of moisture and oxygen. Wrought iron and cast iron have better inherent corrosion resistance due to their slag content and surface properties, while brass (a copper-zinc alloy) is a non-ferrous metal and does not rust.
Correct Answer: A. Brittle
Solution:
Phosphorus is generally considered an impurity in steel. If iron ore has a high phosphorus content (phosphate iron), the resulting steel will also have high phosphorus levels. Phosphorus makes steel brittle, especially at low temperatures (a phenomenon known as cold shortness).
Correct Answer: B. Phosphorus
Solution:
While often an undesirable impurity, small, controlled amounts of phosphorus are sometimes intentionally added to low carbon steels. It acts as a solid-solution strengthener, which raises the yield point, and it also significantly improves the steel's resistance to atmospheric corrosion by helping to form a stable, protective rust layer.
Correct Answer: A. Low carbon steel
Solution:
Mild steel is the most common form of steel and is characterized by its relatively low carbon content, typically between 0.05% and 0.25%. Therefore, it belongs to the low carbon steel category.
Correct Answer: D. Plasticity
Solution:
Plasticity is the ability of a solid material to undergo permanent deformation—a non-reversible change of shape in response to applied forces. Once the stress is removed, the material does not return to its original shape.
Correct Answer: A. wholly pearlite
Solution:
Eutectoid steel is defined as steel with a carbon content of exactly 0.8%. When this steel is cooled slowly, the austenite transforms completely into a single microstructure called pearlite, which is a layered structure of ferrite and cementite.
Correct Answer: C. can cut another metal
Solution:
Hardness is a measure of a material's resistance to localized plastic deformation such as scratching or indentation. A practical and common definition of a hard material is one that can cut another metal (or material) that is softer than it.
Correct Answer: C. from white cast iron by annealing process
Solution:
Malleable cast iron is made from white cast iron, which is hard and brittle. The white iron casting is subjected to a prolonged heat treatment (annealing) which changes the carbon structure, resulting in a material with improved ductility and malleability.
Correct Answer: D. 1.7 to 4.5
Solution:
Cast iron is an iron-carbon alloy with a high carbon content. By definition, its carbon content is greater than that of steel. The typical range for cast iron is from about 2% to 4.5%. The range 1.7 to 4.5% is the most accurate description among the choices.