Correct Answer: B. Copper, Tin and zinc
Solution:
Gunmetal, also known as red brass, is a type of bronze. Its typical composition is an alloy of copper (around 88%), tin (around 10%), and zinc (around 2%). It is known for its strength and resistance to corrosion from steam and saltwater.
Correct Answer: D. Brittleness
Solution:
Non-metals are typically poor conductors of heat and electricity and are not ductile or malleable. Their characteristic property is brittleness, meaning they tend to shatter or break when subjected to stress, rather than deforming.
Correct Answer: B. Wrought iron
Solution:
Wrought iron is the purest form of commercially available iron. It has a very low carbon content (less than 0.08%), which makes it soft, ductile, and fibrous. Cast iron, in contrast, has a high carbon content (over 2%).
Correct Answer: B. Copper and tin
Solution:
The primary definition of bronze is an alloy consisting mainly of copper, with tin as the main additive. Other elements like zinc or phosphorus can be added to create specific types of bronze (like gunmetal), but the fundamental components are copper and tin.
Correct Answer: C. Make the steel ductile and of good bending qualities
Solution:
While manganese does contribute to strength and hardness, one of its key roles in low-carbon steel is to combine with sulfur to form manganese sulfide. This prevents the formation of iron sulfide, which can make the steel brittle at hot-working temperatures. By managing the sulfur, manganese helps to maintain and improve the steel's ductility and bending qualities.
Correct Answer: B. 0.15%
Solution:
Low carbon steel, also known as mild steel, has a carbon content that typically ranges from 0.05% to 0.25%. Of the options provided, 0.15% falls squarely within this range and is a very common carbon level for mild steel.
Correct Answer: B. Nonlinear
Solution:
Unlike metals within their elastic limit, rubber does not follow Hooke's Law (stress is proportional to strain). The stress-strain curve for rubber is nonlinear; it shows a large amount of strain for a small amount of stress initially, and then becomes stiffer as it is stretched further.
Correct Answer: D. Uniform strength in all directions
Solution:
Wrought iron is produced by a process that creates a fibrous structure, with slag inclusions drawn out into long filaments. Because of this grain-like structure, its strength is not uniform; it is much stronger when pulled in the direction of the fibers than it is across them. Therefore, the statement that it has uniform strength in all directions is false.
Correct Answer: C. Different crystal structures at different temperatures
Solution:
Allotropy is the property of some chemical elements to exist in two or more different forms, in the same physical state. For solids like iron, this means having different crystal structures at different temperatures. For example, iron exists as Body-Centered Cubic (BCC) at room temperature and changes to Face-Centered Cubic (FCC) at higher temperatures.
Correct Answer: A. Creep
Solution:
Creep is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses. It is a time-dependent deformation that occurs even at stress levels below the material's yield strength, and it is highly dependent on temperature.
Correct Answer: C. Both (A) and (B)
Solution:
Both Blackheart and Whiteheart cast irons are types of malleable cast iron. They are produced by a special heat treatment (annealing) of brittle white cast iron, which changes their microstructure. This process makes them much more ductile and tougher, giving them properties that are similar to those of steel.
Correct Answer: B. The average grain size is a minimum
Solution:
Heating steel to just above its upper critical temperature causes a phase transformation to austenite. This process, known as recrystallization, results in the formation of new, fine grains. This is the point where the average grain size is at its minimum, a process called grain refinement, which is crucial for improving the mechanical properties of the steel.
Correct Answer: C. varies with carbon-content of the steel
Solution:
The critical temperatures of steel (both lower and upper) are defined by the iron-carbon phase diagram. The exact temperature at which phase changes occur varies with the carbon content of the steel. For example, the upper critical temperature (A3) decreases as carbon content increases up to 0.8%.
Correct Answer: B. Product of blast furnace made by reduction of iron ore
Solution:
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. It is the molten iron extracted from the blast furnace, which is then tapped off for further processing into steel or cast iron.
Correct Answer: C. More than
Solution:
A key characteristic of brittle materials like cast iron is that they are very strong in compression but weak in tension. The compressive strength of cast iron is typically three to five times more than its tensile strength. This is because the graphite flakes within its structure act as stress concentrators under tension but do not significantly affect its compressive properties.