Question 1

Process selection in steelmaking — phosphorus in pig iron Evaluate the statement: “The acidic Bessemer (converter) process is suitable for producing steel from pig iron that contains large quantities of phosphorus.” Choose the correct judgment.

Accepted Answer

Introduction / Context: Phosphorus is a harmful impurity in most steels, promoting cold-shortness and brittleness. Whether a steelmaking route can remove phosphorus depends strongly on slag chemistry and converter lining (acidic versus basic). Understanding this compatibility is central to selecting the right process for a given hot metal composition. Given Data / Assumptions: “Acidic Bessemer” uses silica (acid) refractory; “basic Bessemer” (Thomas) uses basic linings and fluxes. High-phosphorus pig iron requires efficient dephosphorisation. Slag basicity governs P removal thermodynamics. Concept / Approach: Phosphorus is removed effectively only in a basic environment where basic oxides (from lime/dolomite) form stable phosphate compounds that partition into slag. Acid-lined converters cannot sustain the lime-rich slags necessary for dephosphorisation, so the acidic Bessemer route is unsuitable for high-P pig iron. The basic (Thomas) process was developed specifically to handle such charges. Step-by-Step Solution: Identify requirement: remove high P.Check slag chemistry: needs high basicity (lime).Acidic lining is incompatible with high-lime slags → poor P removal.Therefore, the statement is incorrect; use the basic process instead. Verification / Alternative check: Historical practice in Europe used the Thomas basic converter to treat high-phosphorus minette ores successfully, confirming the principle. Why Other Options Are Wrong: Options implying “correct” conflict with slag chemistry; adding lime in an acid converter damages the lining; sulfur co-presence does not change the need for basic slag. Common Pitfalls: Assuming oxidation alone removes P; without basic slag, P removal is inefficient. Final Answer: Incorrect

Question 2

Heat treatment practice — definition of process annealing for hypo-eutectoid steels In process annealing of hypo-eutectoid steel, which temperature path is followed and how is the cooling carried out to restore ductility without full austenitisation?

Accepted Answer

Introduction / Context: Process annealing is an intermediate heat treatment used in manufacturing to restore ductility and reduce hardness after cold working, enabling further forming operations. For hypo-eutectoid steels, it is distinct from full annealing and normalising, both of which involve full austenitisation above the upper critical temperature (A3). Given Data / Assumptions: Steel composition is hypo-eutectoid (carbon less than eutectoid). Goal is to soften and relieve work-hardening without major grain growth. No need for complete transformation to austenite. Concept / Approach: Process annealing heats the steel to a temperature below or close to the lower critical temperature (A1). At this subcritical range, recovery and partial recrystallisation occur in the cold-worked ferrite, reducing dislocation density and restoring ductility. Slow cooling avoids introducing new stresses and maintains the softened structure. Step-by-Step Solution: Select subcritical temperature: near or below A1 to target recovery/recrystallisation of ferrite.Avoid full austenitisation (above A3) which would be full annealing/normalising.Cool slowly (often in furnace or still air) to minimize residual stresses and hardness.Hence choose “heated below or close to the lower critical temperature and then cooled slowly”. Verification / Alternative check: Textbook process charts list process annealing for low-carbon steels at approximately 550–700° C (below A1), aligning with the selected option. Why Other Options Are Wrong: Options (a)–(c) describe full annealing/normalising regimes above A3; (e) introduces quenching which hardens instead of softening. Common Pitfalls: Confusing process annealing with spheroidising or full annealing; the purposes and temperature ranges differ. Final Answer: heated below or close to the lower critical temperature and then cooled slowly

Question 3

Objectives of heat treatment — picking the most general statement Heat treatment may be carried out to achieve which of the following outcomes in engineering materials?

Accepted Answer

Introduction / Context: Heat treatment encompasses a family of thermal cycles applied to metals and alloys to tailor properties for service. Different treatments target different metallurgical mechanisms, including stress relief, phase transformations, precipitation, recrystallisation, and grain growth control. Given Data / Assumptions: The question asks for the broad purpose, not a specific cycle. Material examples include ferrous and non-ferrous alloys. Industrial goals include strength, ductility, toughness, and dimensional stability. Concept / Approach: Stress-relief annealing reduces residual stresses; normalising and annealing modify microstructure; processes like recrystallisation anneal change grain size and shape; quench-and-temper adjusts strength–toughness balance. Therefore, heat treatment can accomplish any of the listed objectives depending on the selected process parameters (temperature, time, cooling rate). Step-by-Step Solution: Map objective to treatment: stress relief → subcritical anneal.Modify structure → austenitise and transform (e.g., normalise, quench-temper).Change grain size → recrystallisation/full anneal/controlled cooling.Thus, the most inclusive answer is “any one of these”. Verification / Alternative check: Process–property charts show numerous heat-treatment routes delivering each of these outcomes, confirming the comprehensive option. Why Other Options Are Wrong: Each single option is correct but incomplete; “none” contradicts the well-established purposes of heat treatment. Common Pitfalls: Assuming one treatment meets all goals simultaneously; trade-offs exist (e.g., higher strength may reduce ductility). Final Answer: any one of these

Question 4

Metals in nuclear technology — identifying applicable uses Which of the following metals are used in nuclear-energy applications, considering roles such as fissile fuel, fertile material, and structural or superconducting components?

Accepted Answer

Introduction / Context: Nuclear technology employs several metals for distinct functions: fuels, fertile materials, cladding, structural internals, control rods, and advanced accelerator or reactor systems. Recognizing multiple valid roles prevents an overly narrow view of “nuclear metals”. Given Data / Assumptions: Uranium is a fissile/fertile fuel (e.g., U-235, U-238). Thorium is fertile and can breed fissile U-233 in appropriate reactors. Niobium is used in nuclear contexts (e.g., Nb-containing alloys for corrosion resistance and superconducting Nb-based cavities/magnets in accelerator-driven systems). Concept / Approach: “Used for nuclear energy” does not exclusively mean “used as reactor fuel.” It can include materials essential to the generation, control, or conversion of nuclear energy, including structural and superconducting components. Uranium and thorium are directly tied to fuel cycles; niobium finds application in superconducting radio-frequency cavities and in special alloys exhibiting good corrosion resistance and low activation—supporting nuclear-related infrastructure and advanced systems. Step-by-Step Solution: Identify direct fuels: uranium (fissile) and thorium (fertile).Recognize supporting materials: niobium in superconducting components and specialty alloys linked to nuclear technology.Interpret “used for nuclear energy” broadly but correctly across the ecosystem.Hence, the inclusive answer is “all of these”. Verification / Alternative check: Engineering references list U and Th in fuel cycles; niobium-based superconductors (e.g., Nb-Ti, Nb3Sn) are prevalent in high-field magnets and SRF cavities associated with particle and accelerator technologies used in nuclear science. Why Other Options Are Wrong: Limiting to fuels overlooks essential nuclear-enabling materials; “only uranium and thorium” excludes niobium’s legitimate roles. Common Pitfalls: Interpreting the question as “fuel only”; the broader nuclear engineering context includes critical non-fuel metals. Final Answer: all of these

Question 5

Converter linings — basic versus acidic Bessemer (Thomas) practice In the basic Bessemer (Thomas) steelmaking process, the converter is lined with which refractory so that highly basic slags can be formed for phosphorus removal?

Accepted Answer

Introduction / Context: The choice of converter lining is central to the chemistry of steelmaking. A basic lining withstands lime-rich slags necessary for dephosphorisation, while an acidic lining is compatible with silica-rich slags but cannot remove phosphorus efficiently. Given Data / Assumptions: Process considered: basic Bessemer (Thomas). Target: phosphorus removal using basic slag (lime/dolomite). Refractory must resist chemical attack from basic oxides. Concept / Approach: Dolomite (CaO·MgO) baked with tar binders yields a basic refractory suitable for the Thomas converter. It tolerates high-basicity slags and supports reactions that transfer phosphorus from the metal to the slag as stable phosphates. Silica bricks, in contrast, are acid refractories and react unfavorably with basic slags, making them unsuitable for the Thomas route. Step-by-Step Solution: Identify need: basic lining for basic slag and P removal.Select refractory: tar-bonded burnt dolomite bricks provide the required basicity and resistance.Exclude acid refractories (silica) that hinder lime-rich slag practice.Therefore, pick “a mixture of tar and burnt dolomite bricks”. Verification / Alternative check: Classic steelmaking texts list Thomas converters with dolomite or magnesia-based linings for high-basicity operation. Why Other Options Are Wrong: Silica bricks are for acid practice; “either” ignores chemical incompatibility; “none” and “pure magnesia only” do not reflect the historical standard for Thomas converters described in many curricula. Common Pitfalls: Confusing basic oxygen steelmaking (modern BOF) with historical Bessemer variants; both require careful lining selection based on slag chemistry. Final Answer: a mixture of tar and burnt dolomite bricks

Question 6

Heat treatment temperatures — full annealing of hyper-eutectoid steel For full annealing of a hyper-eutectoid steel (carbon greater than eutectoid), the appropriate furnace temperature relative to the critical points is typically:

Accepted Answer

Introduction / Context: Hyper-eutectoid steels contain excess cementite at equilibrium. Full annealing aims to refine structure and soften the alloy for machining or shaping. The chosen temperature window must transform the pearlitic matrix while avoiding excessive dissolution and coarsening of proeutectoid cementite along grain boundaries. Given Data / Assumptions: Hyper-eutectoid composition (C > eutectoid). Goal: produce a coarse pearlitic/ferrite-carbide structure after slow cooling. Critical points: lower critical (A1) and Acm (upper limit for cementite dissolution). Concept / Approach: For hyper-eutectoid steel, full annealing is commonly performed by heating above A1 but below Acm, typically around 30–50° C above A1. This austenitises the pearlite but keeps most proeutectoid cementite undissolved, preventing grain-boundary cementite networks from dissolving and later coarsening unfavorably. Very high temperatures risk grain growth and undesirable carbide morphology. Step-by-Step Solution: Select temperature: A1 + 30–50° C (i.e., slightly above the lower critical).Hold for homogenization; then cool slowly in the furnace to promote coarse pearlite.Avoid heating above Acm (option a/e), which can over-dissolve carbides and coarsen grains.Hence, choose “30° C to 50° C above lower critical temperature”. Verification / Alternative check: Heat-treatment charts specify sub-Acm anneals for hyper-eutectoid steels to control carbide distribution and machinability. Why Other Options Are Wrong: Above upper critical (a) applies to hypo-eutectoid full anneal; (b) and (d) lie below transformation range; (e) suggests quenching, not annealing. Common Pitfalls: Using the same rule as hypo-eutectoid steels (above A3) for hyper-eutectoid compositions; they require a different window relative to Acm. Final Answer: 30° C to 50° C above lower critical temperature

Question 7

Critical Temperatures in Steel — Variation of the Upper Critical Point (A3) State whether the following statement is correct: “The upper critical temperature (A3) of steel varies with the carbon content.”

Accepted Answer

Introduction / Context: The iron–carbon phase diagram defines several critical temperatures that govern transformations during heating and cooling. One of these is the upper critical point (A3) for hypo-eutectoid steels, above which the structure is fully austenitic. Understanding how A3 changes with carbon content is foundational for selecting heat-treatment temperatures such as normalising and hardening. Given Data / Assumptions: A3 refers to the upper critical temperature for hypo-eutectoid steels (less than about 0.8% carbon). Steel composition varies by carbon content while other alloying elements are assumed minimal. Equilibrium (slow) heating conditions are considered for conceptual clarity. Concept / Approach: As the percent carbon increases from very low levels toward the eutectoid composition, the A3 line on the Fe–C diagram slopes downward. This means the required temperature to achieve complete austenitisation decreases as carbon increases (up to the eutectoid point). For hyper-eutectoid steels, the relevant line is Acm rather than A3; nonetheless, the statement that the upper critical “varies with carbon” is correct when read as a general observation that critical temperatures in steels depend on composition. Step-by-Step Solution: Recognise that A3 is composition-dependent within the hypo-eutectoid range.Note the trend: increasing carbon content → lower A3 temperature until the eutectoid point.For hyper-eutectoid steels, Acm applies; this also varies with carbon, reinforcing the general idea that critical temperatures are composition-dependent.Therefore, the statement “A3 varies with carbon content” is correct. Verification / Alternative check: Consult any standard Fe–C diagram: the A3 boundary is not horizontal; it is a sloped line dependent on carbon percentage. Why Other Options Are Wrong: False: contradicts the phase diagram which clearly shows a carbon dependence.“Only for hypo-” or “only for hyper-”: critical lines (A3 or Acm) change with carbon in their respective ranges; limiting it to one range is misleading. Common Pitfalls: Assuming fixed critical temperatures for all steels; alloying and carbon shift these temperatures. Final Answer: True

Question 8

Microstructure–Property Link — Ferrite and Pearlite in Steel A steel whose microstructure consists predominantly of ferrite and pearlite will typically be:

Accepted Answer

Introduction / Context: Mechanical properties of steels are dictated by their microstructures. Ferrite is a relatively soft, ductile phase, while pearlite is a lamellar mixture of ferrite and cementite offering higher strength and hardness than ferrite alone. Mild and medium-low carbon steels commonly exhibit a ferrite–pearlite mixture, leading to a desirable balance of ductility and strength for general engineering use. Given Data / Assumptions: Microstructure contains ferrite plus pearlite (typical of low or medium-low carbon steel in the normalised or cooled state). No martensite, bainite, or strong precipitation hardening assumed. Room-temperature behavior considered. Concept / Approach: Ferrite contributes ductility and toughness. Pearlite contributes strength and some hardness due to the alternating ferrite–cementite lamellae. The combination yields steels that are not extremely hard but resist impact and bending reasonably well. Thus, the standout descriptor among the choices is “tough,” reflecting the ability to absorb energy before fracture, rather than “hard,” which would imply higher resistance to indentation typical of quenched/martensitic structures. Step-by-Step Solution: Identify properties of ferrite: soft, ductile → contributes toughness.Identify properties of pearlite: stronger and harder than ferrite but still reasonably ductile.Combine effects: overall moderate strength with good toughness; not especially hard.Select “tough” as the most appropriate single-word descriptor. Verification / Alternative check: Typical Charpy impact and elongation values for low-carbon ferrite–pearlite steels are higher than those of fully pearlitic or martensitic steels of similar carbon content, indicating better toughness. Why Other Options Are Wrong: Hard: excessive; martensitic or tempered martensitic structures are harder.Soft: incomplete; the presence of pearlite raises strength above very soft ferritic iron.Hard and tough: overstates hardness for this microstructure at comparable carbon levels. Common Pitfalls: Equating “strength” with “hardness”; they correlate but are not identical measures. Final Answer: tough

Question 9

Alloying for Impact Toughness — Improving Shock Resistance of Steel Shock (impact) resistance in steels is most effectively increased by adding:

Accepted Answer

Introduction / Context: Shock resistance, or impact toughness, reflects the ability of a material to absorb energy without fracturing. Alloying elements influence toughness differently: some increase hardness and wear resistance, while others improve ductility and toughness, particularly at low temperatures. Given Data / Assumptions: Plain carbon steel base composition. Comparative effect of common alloying elements on impact toughness. Room to low-temperature service is relevant. Concept / Approach: Nickel is well known to enhance toughness and reduce ductile-to-brittle transition temperature in steels. It improves impact behavior without excessively increasing hardness or promoting brittle phases. Chromium, while valuable for hardenability and wear/corrosion resistance, tends to raise hardness and, unless balanced, can reduce toughness. Additions like sulphur, lead, and phosphorus primarily improve machinability (S, Pb) or strength at the expense of toughness (P), and therefore do not improve shock resistance. Step-by-Step Solution: Identify property target: higher impact toughness, not just hardness.Map alloy influences: Ni → toughness; Cr → hardness/wear; S/Pb/P → machinability or embrittlement.Choose the element with the most direct, consistent positive impact on shock resistance: nickel. Verification / Alternative check: Low-temperature structural steels often contain nickel to maintain toughness; standards specify Ni additions for improved Charpy V-notch values. Why Other Options Are Wrong: Chromium alone does not primarily enhance impact toughness; it is more associated with hardenability and wear.Nickel and chromium together can be balanced in alloy steels, but “nickel” alone cleanly captures the principal toughening effect.Sulphur, lead, phosphorus degrade toughness or target machinability, not impact resistance. Common Pitfalls: Assuming higher hardness automatically means better impact resistance; often the opposite is true. Final Answer: nickel

Question 10

Deoxidation & Soundness — Additions to Low-Carbon Steels Which element is commonly added to low-carbon steels to prevent porosity by deoxidising the melt and promoting sound ingots?

Accepted Answer

Introduction / Context: Porosity in steel cast products often results from dissolved gases and oxides formed during solidification. Deoxidation practice in steelmaking is crucial for producing sound ingots and continuous-cast products with minimal blowholes and piping defects. Given Data / Assumptions: Melt treatment focuses on removing dissolved oxygen to avoid gas porosity. Alloying levels are typical of low-carbon steels. Standard deoxidisers are considered. Concept / Approach: Silicon is a strong deoxidiser. Added as ferrosilicon, it reacts with dissolved oxygen to form stable silica, thereby reducing gas evolution and porosity. Aluminium is another powerful deoxidiser (killed steels), but among the listed choices, silicon best represents the common practice. Manganese chiefly combines with sulphur to form MnS and prevent hot shortness; it is not the primary deoxidiser for porosity control. Sulphur and phosphorus are generally undesirable — they embrittle and do not prevent porosity. Step-by-Step Solution: Identify the defect: porosity from gases/oxides during solidification.Choose a strong deoxidiser: silicon (and aluminium in many practices) remove dissolved oxygen.Rule out Mn as a deoxidiser of first choice; it targets S control (hot shortness).Exclude S and P; both are impurities that worsen toughness and do not reduce porosity. Verification / Alternative check: Steelmaking texts list “rimming, capped, semi-killed, killed” steels; silicon and aluminium additions move steel toward semi-killed/killed conditions with improved soundness. Why Other Options Are Wrong: Sulphur: increases hot shortness and inclusions; not a deoxidiser.Phosphorus: raises strength but reduces toughness; not for deoxidation.Manganese: useful for sulphur control, not primarily to prevent porosity. Common Pitfalls: Confusing sulphur control (Mn additions) with oxygen removal (Si/Al deoxidation). Final Answer: Silicon

Question 11

Nickel–Chromium–Iron Alloys — Identifying Inconel Composition Which of the following nominal compositions most closely represents a classic Inconel (Ni–Cr–Fe) alloy grade?

Accepted Answer

Introduction / Context: “Inconel” denotes a family of nickel-based alloys (notably Ni–Cr–Fe types like 600/601/625, etc.) used for high-temperature strength, oxidation resistance, and corrosion resistance. While exact compositions vary by grade, their hallmark is a high nickel base with significant chromium and some iron. Given Data / Assumptions: We are comparing approximate, nominal compositions. Focus is on a representative Ni–Cr–Fe Inconel-type composition rather than Cu-bearing nickel alloys. Properties derive from solid-solution and, in some grades, precipitation strengthening. Concept / Approach: Classic Inconel Ni–Cr–Fe alloys typically contain ~70–76% Ni, ~14–17% Cr, and ~6–10% Fe (ranges depend on specific grade). Option (d) — 80% Ni, 14% Cr, 6% Fe — aligns closely with the Ni-rich, Cr- and Fe-containing profile of Inconel 600-type alloys. Option (b) is a Ni–Cu alloy (Monel family), not Inconel. Option (c) lacks iron and looks more like a binary Ni–Cr; option (a) has lower Ni and higher Fe than standard Inconel baselines. Step-by-Step Solution: Identify Inconel family: Ni–Cr–Fe foundation with high Ni content.Match each option to that pattern: (d) fits the canonical Ni–Cr–Fe ratios best.Eliminate non-matching chemistries: (b) is Monel-like; (c) lacks Fe; (a) is lower-Ni than typical Inconel grades. Verification / Alternative check: Manufacturer datasheets for Inconel 600 list Ni ~72 min, Cr 14–17, Fe 6–10, consistent with answer (d) in nominal terms. Why Other Options Are Wrong: (b) Represents Monel-type Ni–Cu alloy, not Inconel.(c) Omits iron; not representative of Ni–Cr–Fe Inconel grades.(a) Underrepresents nickel relative to typical Inconel compositions. Common Pitfalls: Assuming all nickel alloys with chromium are “Inconel”; composition families are distinct (Monel, Hastelloy, Inconel, etc.). Final Answer: 80% nickel, 14% chromium and 6% iron

Question 12

Cementite (Iron Carbide, Fe3C) — Chemical Composition by Mass Cementite in steels and cast irons consists of which approximate mass percentages of carbon and iron?

Accepted Answer

Introduction / Context: Cementite (Fe3C) is an intermetallic compound central to the microstructures of steels and cast irons. Its composition determines the carbon balance in phases such as pearlite and influences the hardness and brittleness of iron–carbon alloys. Given Data / Assumptions: Fe3C stoichiometry is fixed: three iron atoms to one carbon atom. Atomic masses (approx.): Fe ≈ 55.85, C ≈ 12.01. Mass percentages are required, not atomic fractions. Concept / Approach: The mass fraction of carbon in Fe3C can be computed using the molecular mass: 355.85 + 12.01 ≈ 179.56. Carbon contribution ≈ 12.01/179.56 ≈ 0.0669 or 6.69%, commonly cited as 6.67%. Iron is the remainder, 93.33% by mass. This classic figure appears in phase-diagram discussions and is the anchor point for understanding eutectoid and eutectic compositions involving cementite. Step-by-Step Solution: Compute total mass: 355.85 + 12.01 ≈ 179.56.Compute carbon percent: 12.01 / 179.56 ≈ 0.0669 → 6.67% (rounded).Compute iron percent: 100% − 6.67% = 93.33%.Report composition: 6.67% C and 93.33% Fe. Verification / Alternative check: Standard metallurgy references list cementite as Fe3C ≈ 6.67% C by weight. Why Other Options Are Wrong: Options involving “ferrite” mix phase names with mass percentages; ferrite is a separate phase (α-Fe), not a component of cementite.13% carbon is far too high and inconsistent with Fe3C stoichiometry. Common Pitfalls: Confusing atomic percent with weight percent; Fe3C has only 1 in 4 atoms as carbon but still only 6.67 wt% C. Final Answer: 6.67% carbon and 93.33% iron

Question 13

Cast Irons — Relative Softness of Gray vs. White Iron Fill in the blank: Gray cast iron is __________ than white cast iron.

Accepted Answer

Introduction / Context: Gray and white cast irons differ in the form taken by carbon during solidification. The microstructural form of carbon controls hardness, machinability, wear resistance, and fracture behavior. Recognising these differences is essential for selecting cast irons for machine bases, wear parts, or hard liners. Given Data / Assumptions: Gray iron contains flake graphite in a ferrite/pearlite matrix. White iron solidifies as iron carbide (cementite) networks (ledeburite), with little to no free graphite. Properties are considered at room temperature. Concept / Approach: Flake graphite in gray iron interrupts the metal matrix, lowering hardness and strength but greatly improving machinability and damping. White iron’s cementite-rich structure is very hard and brittle, giving high wear resistance but poor machinability. Therefore, gray iron is characteristically softer than white iron. Step-by-Step Solution: Identify carbon morphology: graphite flakes (gray) vs. cementite networks (white).Map morphology to hardness: graphite → softer; cementite → harder.Conclude gray iron is softer than white iron. Verification / Alternative check: Hardness measurements: gray iron typically shows lower Brinell hardness than white iron of similar composition. Why Other Options Are Wrong: Harder: contradicts the microstructural basis.Stronger in tension: gray iron has relatively low tensile strength due to flake graphite stress concentrators.More brittle: white iron is generally more brittle because of cementite. Common Pitfalls: Assuming all cast irons are hard; gray irons are intentionally softer for machinability and damping. Final Answer: softer

Question 14

Chemical Bonding — Electron Transfer Between Atoms The type of chemical bond formed primarily by transfer of electrons from one atom to another is called:

Accepted Answer

Introduction / Context: Materials science connects atomic bonding with macroscopic properties such as melting point, electrical conductivity, and plasticity. The major bonding types are ionic, covalent, and metallic, each associated with specific electron arrangements and energy landscapes. Given Data / Assumptions: Two atoms with different electronegativities interact. One atom tends to donate electrons; the other tends to accept. Resulting species are ions with electrostatic attraction. Concept / Approach: In an ionic bond, one or more electrons are transferred from a less electronegative atom (often a metal) to a more electronegative atom (often a non-metal). The resulting cations and anions attract electrostatically, forming a crystal with high lattice energy. This differs from covalent bonding, where electrons are shared, and metallic bonding, where valence electrons are delocalised to form an electron cloud around positive ion cores. Step-by-Step Solution: Identify electron transfer process: donor atom → electron loss → cation; acceptor atom → electron gain → anion.Recognise strong Coulombic attraction between oppositely charged ions.Match to bond type: ionic bond is defined by electron transfer and electrostatic attraction. Verification / Alternative check: Classic examples include NaCl, MgO, and CaF2; their crystal structures and properties (high melting points, brittleness) support ionic bonding. Why Other Options Are Wrong: Covalent bonds involve shared electron pairs, not net transfer.Metallic bonds feature a delocalised electron “sea,” not discrete ion pairs from transfer.“None of these” is incorrect because the named type is well established. Common Pitfalls: Assuming mixed bonding cannot exist; many solids have partial ionic/covalent character, but the defining mechanism here is transfer. Final Answer: ionic bond

Question 15

Duralumin (Al–Cu Alloy) — Identifying the Incorrect Statement Which of the following statements about duralumin is incorrect?

Accepted Answer

Introduction / Context: Duralumin refers to a family of age-hardenable aluminium–copper alloys (typically with Mg and Mn), long used in aerospace for their excellent strength-to-weight ratio and good fabrication characteristics. Knowing their key characteristics helps in materials selection and design. Given Data / Assumptions: Duralumin contains significant Cu (and minor Mg, Mn), enabling precipitation hardening. We compare qualitative statements about properties and processing. Density comparison is made against pure aluminium. Concept / Approach: Age hardening (natural or artificial) is a hallmark of Al–Cu alloys: solution treat, quench, and age to form finely dispersed precipitates, increasing strength. Duralumin can be forged and generally machines well. However, adding copper and other alloying elements slightly increases density compared to pure aluminium; therefore, it is not “lighter” than pure aluminium. The strength benefits come from microstructural changes, not reduced density. Step-by-Step Solution: Identify true attributes: age hardening capability → true.Forming routes: forging and machining are common → true.Density logic: alloying additions raise density relative to pure Al → the statement “lighter than pure aluminium” is incorrect. Verification / Alternative check: Typical densities: pure Al ≈ 2.70 g/cm^3; Al–Cu alloys slightly higher due to heavier alloying additions, confirming the incorrectness of option (d). Why Other Options Are Wrong (as the “incorrect” choice): Options (a), (b), and (c) are established characteristics of duralumin. Common Pitfalls: Equating “high strength-to-weight” with “lower density.” Duralumin’s advantage is higher strength at about the same or slightly higher density, not lower mass density. Final Answer: It is lighter than pure aluminium

Question 16

Material Classification — Is Cast Iron a Ductile Material? Evaluate the statement: “Cast iron is a ductile material.” Choose the most accurate response for general cast irons used in practice.

Accepted Answer

Introduction / Context: “Cast iron” covers several families: gray, white, malleable, and spheroidal graphite (SG or ductile iron). Their mechanical behavior varies widely with graphite morphology and matrix structure. In everyday engineering language, “cast iron” is often associated with gray iron, which is not generally considered ductile. Given Data / Assumptions: Room-temperature mechanical behavior is considered. Generic, unmodified gray/white cast irons are implied unless specified. Understanding that special grades (SG iron) exist but are exceptions. Concept / Approach: Gray and white irons are typically brittle at room temperature. Gray iron contains flake graphite that acts as stress concentrators, lowering tensile strength and ductility though providing good damping and machinability. White iron contains cementite networks, giving very high hardness and brittleness. Only specially produced SG (ductile) iron, with graphite in nodular form, offers significant ductility and toughness. Therefore, as a general statement, “cast iron is ductile” is incorrect. Step-by-Step Solution: Distinguish cast iron families by graphite form: flake (gray) vs. nodular (SG) vs. carbide (white).Relate morphology to properties: flake/carbide → brittle; nodular → improved ductility.Interpret the blanket statement: for “cast iron” without qualification, the safe generalisation is non-ductile at room temperature. Verification / Alternative check: Tensile elongation data: gray/white irons show very low elongation (often near 0–1%), whereas SG irons may show 5–20% depending on grade. Why Other Options Are Wrong (as general statements): “Correct”: too broad; typical cast irons are not ductile.“Correct only for SG iron”: while true for that subset, the prompt asks about cast iron generally.“Correct only at elevated temperature”: not the standard way to classify room-temperature ductility. Common Pitfalls: Assuming all “cast irons” behave like ductile iron; SG iron is a specialised, nodular graphite product. Final Answer: Incorrect

Question 17

Critical temperatures in the iron–carbon system (eutectoid steel) For a plain carbon steel containing exactly 0.8% carbon (eutectoid composition), how many distinct critical temperatures exist during slow heating or cooling under equilibrium conditi…

Accepted Answer

Introduction / Context: Critical points (or critical temperatures) in the iron–carbon diagram mark transformations between phases such as ferrite, austenite, and cementite. Knowing how many critical temperatures a steel has at a given composition helps predict microstructures and heat-treatment behavior. The special case is eutectoid steel at about 0.8% carbon. Given Data / Assumptions: Plain carbon steel with 0.8% C (eutectoid composition). Slow, near-equilibrium heating or cooling. Standard critical temperatures: lower critical (A1), upper critical for hypoeutectoid (A3), and for hypereutectoid (Acm). Concept / Approach: At the eutectoid composition, the upper and lower boundaries of the austenite field meet at a single temperature (approximately 727°C). Thus A3 and Acm coincide with A1. Eutectoid steel transforms between austenite and pearlite entirely at this single temperature under equilibrium cooling or heating, unlike hypo- or hypereutectoid steels which cross two different critical lines (A1 plus A3 or A1 plus Acm). Step-by-Step Solution: Identify composition: 0.8% C → eutectoid.Recall diagram geometry: the A3 and Acm lines converge to the eutectoid point at A1.Conclude: only one critical temperature is encountered. Verification / Alternative check: Metallographic observation shows fully pearlitic structure below A1 and fully austenitic above A1 for eutectoid steel; no additional proeutectoid ferrite or cementite forms at another temperature, confirming a single critical point. Why Other Options Are Wrong: No critical point: incorrect; austenite↔pearlite transformation still occurs. Two or three points: true for non-eutectoid compositions, not for eutectoid. Any number: physically meaningless in this context. Common Pitfalls: Confusing eutectoid (solid-state reaction at ~727°C) with eutectic; assuming hypo/hypereutectoid behavior applies at 0.8% C. Final Answer: there is only one critical point

Question 18

Fundamental material property — term for permanent retention of deformation Which property name describes a material's ability to retain deformation permanently after removal of the applied load (i.e., non-recoverable strain)?

Accepted Answer

Introduction / Context: In mechanics of materials, engineers distinguish between elastic behavior (recoverable strain) and plastic behavior (permanent strain). Correct terminology matters for forming processes, failure analyses, and setting allowable limits in design standards. Given Data / Assumptions: The load is high enough to exceed the elastic limit of the material. After unloading, the deformation that remains is permanent (plastic). Common related terms include ductility, malleability, brittleness, and resilience. Concept / Approach: Plasticity = ability to undergo non-recoverable (permanent) deformation without fracture.It is a general term encompassing both tensile and compressive plastic flow. Ductility is specifically the ability to undergo significant plastic deformation in tension before fracture (e.g., measured by elongation or reduction of area). Malleability refers commonly to plastic deformation in compression (e.g., rolling, hammering). Brittleness is the tendency to fracture with minimal plastic deformation. Resilience is energy stored elastically and recovered upon unloading. Step-by-Step Solution: Identify the phenomenon: deformation persists after unloading → plastic strain.Map to the correct umbrella term: plasticity.Differentiate from ductility/malleability which are directional subsets of plasticity. Verification / Alternative check: Stress–strain curves show that beyond yield, unloading follows a line parallel to the elastic modulus, leaving a permanent offset strain — this residual is the hallmark of plasticity. Why Other Options Are Wrong: Brittleness: implies little to no plastic deformation. Ductility/malleability: subsets of plasticity in tension or compression, not the general definition asked. Resilience: pertains to elastic energy storage, not permanent deformation. Common Pitfalls: Using “ductility” whenever permanent deformation occurs, even in compression or shear; equating resilience with strength. Final Answer: plasticity

Question 19

Blast furnace anatomy — name the zone below the widest section In a conventional blast furnace, what is the name of the region located immediately below the widest cross-section (belly), where the furnace wall tapers inward toward the hearth?

Accepted Answer

Introduction / Context: Identifying blast furnace zones is essential for understanding gas flow, heat transfer, and reaction progress in ironmaking. Each region has distinct geometry and functions that influence charging practice and tuyere operations. Given Data / Assumptions: The widest section is called the belly. The region below the belly narrows toward the hearth. Standard blast furnace components include throat, stack, belly, bosh, and hearth. Concept / Approach: The bosh is the frustoconical section below the belly where the furnace tapers inward. It houses the tuyeres (through the bosh jacket) and endures intense thermal and chemical attack. Below the bosh lies the hearth, which collects molten hot metal and slag. Above the belly is the stack, and at the very top is the throat where burden materials are charged. Step-by-Step Solution: Locate the widest section: belly.Identify the immediately lower, narrowing zone: bosh.Confirm adjacent regions: hearth below; stack above the belly; throat at the top. Verification / Alternative check: Engineering schematics of blast furnaces consistently label the inward-tapered section below the belly as the bosh; tuyere level is associated with the bosh. Why Other Options Are Wrong: Hearth: is the bottom reservoir for molten products. Stack: situated above belly/throat; not below the widest section. Throat: top charging area. Bustle: refers to bustle pipe (wind distribution ring), not a furnace zone. Common Pitfalls: Confusing the bosh with hearth because both are hot zones; misplacing the stack relative to the belly. Final Answer: bosh

Question 20

Pearlite composition check — weight fractions of constituents Evaluate the statement: “Pearlite is a combination of 87% ferrite and 13% cementite (by weight).” Is this statement correct for eutectoid pearlite?

Accepted Answer

Introduction / Context: Pearlite is the lamellar microconstituent formed at the eutectoid temperature in plain carbon steels. It is composed of alternating plates of ferrite and cementite. Knowing its approximate constituent proportions is useful for quick property estimates and for validating microstructural descriptions in exams and practice. Given Data / Assumptions: Plain carbon steel at eutectoid composition (~0.8% C). Slow cooling to form well-developed pearlite. Composition percentages interpreted as weight fractions. Concept / Approach: At the eutectoid point, the lever rule applied on the Fe–Fe3C diagram gives approximately 88% ferrite and 12% cementite by weight in pearlite. Many texts round this to 87% ferrite and 13% cementite for simplicity. While exact values can vary slightly with temperature rounding and data sources, the commonly accepted approximation 87/13 captures the essence of eutectoid pearlite composition by weight. Step-by-Step Solution: Use the lever rule at eutectoid temperature to split austenite into ferrite and cementite.Compute approximate weight fractions: ferrite ≈ 0.88, cementite ≈ 0.12.Recognize standard rounding: 87% and 13% are widely accepted approximations. Verification / Alternative check: Microstructure atlases and many metallurgy textbooks quote pearlite as roughly 7/8 ferrite and 1/8 cementite by weight, aligning with the 87/13 statement. Why Other Options Are Wrong: “No”: contradicts established approximations for eutectoid pearlite. “Only for hypo/hypereutectoid”: pearlite itself at eutectoid has fixed fraction; hypo-/hyper-eutectoid steels contain proeutectoid phases in addition to pearlite. “True only by volume”: the classic 87/13 figure is a weight fraction approximation, not strictly a volume fraction. Common Pitfalls: Mixing up weight and volume fractions; misquoting the figures as 13% ferrite and 87% cementite (reversed). Final Answer: Yes

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