Correct Answer: D. Pulverised coal injection
Solution:
Pulverised Coal Injection (PCI) is a technology where fine coal powder is directly injected into the blast furnace. This process allows for the partial replacement of metallurgical coke, which is very energy-intensive to produce. By reducing the amount of coke needed, PCI significantly saves energy and reduces the overall cost of steel production.
Correct Answer: C. 57-63%
Solution:
Muntz metal is a type of brass (an alloy of copper and zinc). Specifically, it is defined by its copper content, which is typically around 60% (within the 57-63% range), with the remaining 40% being zinc and trace amounts of other elements.
Correct Answer: C. Blast furnace slag
Solution:
When iron ore is melted in a blast furnace with coke and limestone to produce pig iron, the impurities (like silica and alumina from the ore) combine with the limestone to form a molten layer that floats on top of the iron. This layer, when cooled, is known as blast furnace slag.
Correct Answer: B. Increasing the carbon content in steel increases the yield stress and reduces the ductility.
Solution:
Carbon is the primary hardening agent in steel. As the carbon content increases, the steel becomes harder and stronger, which means its yield stress increases. However, this increase in hardness comes at the cost of making the material more brittle, thus reducing its ductility (its ability to deform without fracturing).
List 1 (Property)
A. Ductility
B. Brittleness
C. Toughness
D. Malleability
List 2 (Description)
1. Material can withstand heavy shock loads
2. Material can be hammered into sheets without rupture
3. Material can be drawn out into wires without necking down
4. Material fail suddenly without warning
Correct Answer: A. A-3, B-4, C-1, D-2
Solution:
The correct matches are based on the definitions of these mechanical properties:
- Ductility (A) is the ability to be drawn into a wire (3).
- Brittleness (B) is the tendency to fail suddenly without significant deformation (4).
- Toughness (C) is the ability to absorb energy and withstand shock loads (1).
- Malleability (D) is the ability to be hammered or rolled into thin sheets (2).
ST1: Mild steel has higher ultimate tensile strength when compared to High Carbon Steel.
ST2: TOR steel is high strength deformed bars with high yield and bond strength.
Correct Answer: B. ST1 is false and ST2 is true.
Solution:
ST1 is false: High Carbon Steel is harder and stronger than mild steel, meaning it has a higher ultimate tensile strength.
ST2 is true: TOR steel is a brand of cold-twisted deformed (ribbed) rebar, which is known for its high yield strength and excellent bond with concrete due to the deformations.
Correct Answer: D. Pig iron
Solution:
The direct product of smelting iron ore in a blast furnace is pig iron. It is a crude, high-carbon form of iron that is then further processed to create other materials like cast iron, wrought iron, and steel.
Correct Answer: B. Galvanizing
Solution:
The process of applying a protective zinc coating to iron or steel to prevent rusting is called galvanizing. The most common method is hot-dip galvanizing, where the parts are submerged in a bath of molten zinc.
Correct Answer: D. 3% to 4%
Solution:
Pig iron is the crude iron produced in a blast furnace. It is characterized by its high carbon content, which typically ranges from 3% to 4.5%. This high carbon content makes it brittle.
Correct Answer: A. Durability
Solution:
Durability is the measure of a material's ability to withstand wear, pressure, or damage over time. It directly relates to the material's lifespan and its capacity to remain functional without significant deterioration.
Correct Answer: A. Wrought iron
Solution:
Among the given options, wrought iron is the purest form of commercial iron, containing a very low amount of carbon (typically less than 0.08%). Pig iron has the highest carbon content, followed by cast iron and then mild steel.
Correct Answer: B. Occur along an oblique plane
Solution:
Cast iron is a brittle material, meaning it is much weaker in shear than in compression. When compressed, the maximum shear stress occurs on planes at a 45° angle to the load. Therefore, the material fails in shear along these oblique planes.
Important Note: While technically correct, some exam keys may list (C) as the answer under a simplified view of brittle failure. However, failure due to shear on an oblique plane is the more accurate engineering explanation.
Correct Answer: C. Dressing
Solution:
Dressing of ore (also known as beneficiation) is the initial step after mining. It involves the mechanical processes of cleaning, crushing, and concentrating the ore to remove unwanted earthy and clay-like impurities (gangue) before smelting.
Correct Answer: A. Bauxite
Solution:
Bauxite is the primary ore from which almost all of the world's aluminium is extracted. It is a sedimentary rock rich in aluminium oxides.
Correct Answer: A. Au
Solution:
Gold (Au) is a noble metal, meaning it is highly resistant to corrosion and oxidation. Because of its low chemical reactivity, it is one of the few metals that can be found in nature in its native or free state, not combined with other elements in an ore.