Q: Steel transformations — hyper-eutectoid equilibrium product: Under equilibrium (slow) cooling from the austenitic state, a hyper-eutectoid plain carbon steel will consist of:

Introduction / Context: Interpreting the iron–carbon diagram is essential for predicting microstructures after equilibrium cooling. The products differ depending on whether the composition lies below, at, or above the eutectoid point (0.8% C). Given Data / Assumptions: Composition is hyper-eutectoid (carbon > 0.8%). Cooling is slow enough to approximate equilibrium (no martensite). Plain carbon steel with no alloying complications. Concept / Approach: For hyper-eutectoid steels, as the alloy cools from austenite, proeutectoid cementite forms first along grain boundaries. At the eutectoid temperature, the remaining austenite transforms into pearlite. Therefore, the final microstructure contains pearlite plus proeutectoid cementite. Ferrite is the proeutectoid phase only for hypo-eutectoid steels; martensite requires rapid quenching; bainite forms under specific non-equilibrium isothermal or continuous-cooling conditions. Step-by-Step Solution: Start above the eutectoid: fully austenitic.On cooling, form proeutectoid cementite at grain edges.At eutectoid temperature, remaining austenite → pearlite.Result: pearlite + proeutectoid cementite. Verification / Alternative check: Textbook micrographs show pearlite colonies bounded by continuous cementite networks in hyper-eutectoid steels. Why Other Options Are Wrong: Ferrite + pearlite corresponds to hypo-eutectoid compositions. Ferrite + bainite and cementite + martensite involve non-equilibrium transformations. Only cementite is impossible for practical carbon ranges and would be extremely brittle. Common Pitfalls: Mixing up proeutectoid phases; assuming similar behaviour on both sides of the eutectoid composition. Final Answer: Cementite and pearlite

Question 1

Bronze families — composition comparison: Consider the statement: “Manganese bronze contains more copper than silicon bronze.” Choose the correct evaluation.

Accepted Answer

Introduction / Context: Trade names like “manganese bronze” and “silicon bronze” often mislead engineers about actual compositions. Understanding the broad families helps avoid specification errors in marine hardware, fasteners, and bearings where strength and corrosion resistance matter. Given Data / Assumptions: Manganese bronze is commonly a high-strength brass (Cu–Zn) with Mn and sometimes Al/Fe; its copper content is typically much lower than 90%. Silicon bronze is Cu-rich, generally around 94–97% Cu with ~2–4% Si and minor Mn. We compare representative compositions, not an extreme proprietary grade. Concept / Approach: Typical manganese bronze grades have copper around 55–65% with substantial zinc, plus manganese for strength/hardness. In contrast, silicon bronze has copper in the mid-90% range. Therefore, the assertion that manganese bronze contains more copper than silicon bronze is false for standard engineering grades; in fact, silic on bronze generally contains significantly more copper. Step-by-Step Solution: List typical Cu contents: manganese bronze ~60% Cu; silicon bronze ~95% Cu.Compare numerically: 60% < 95%.Conclude the statement is incorrect.Answer: No. Verification / Alternative check: Standards/catalogues for C86300-type manganese bronze versus C65500-type silicon bronze show the copper percentages aligning with the above comparison. Why Other Options Are Wrong: “Only for high-manganese variants” and “depends on heat treatment” do not change the basic composition reality. “Both contain the same copper percentage” contradicts standard grades. Common Pitfalls: Equating the word “bronze” with “very high copper content” across all families; confusing brass (Cu–Zn) based bronzes with true bronzes. Final Answer: No

Question 2

Steel transformations — hyper-eutectoid equilibrium product: Under equilibrium (slow) cooling from the austenitic state, a hyper-eutectoid plain carbon steel will consist of:

Accepted Answer

Introduction / Context: Interpreting the iron–carbon diagram is essential for predicting microstructures after equilibrium cooling. The products differ depending on whether the composition lies below, at, or above the eutectoid point (0.8% C). Given Data / Assumptions: Composition is hyper-eutectoid (carbon > 0.8%). Cooling is slow enough to approximate equilibrium (no martensite). Plain carbon steel with no alloying complications. Concept / Approach: For hyper-eutectoid steels, as the alloy cools from austenite, proeutectoid cementite forms first along grain boundaries. At the eutectoid temperature, the remaining austenite transforms into pearlite. Therefore, the final microstructure contains pearlite plus proeutectoid cementite. Ferrite is the proeutectoid phase only for hypo-eutectoid steels; martensite requires rapid quenching; bainite forms under specific non-equilibrium isothermal or continuous-cooling conditions. Step-by-Step Solution: Start above the eutectoid: fully austenitic.On cooling, form proeutectoid cementite at grain edges.At eutectoid temperature, remaining austenite → pearlite.Result: pearlite + proeutectoid cementite. Verification / Alternative check: Textbook micrographs show pearlite colonies bounded by continuous cementite networks in hyper-eutectoid steels. Why Other Options Are Wrong: Ferrite + pearlite corresponds to hypo-eutectoid compositions. Ferrite + bainite and cementite + martensite involve non-equilibrium transformations. Only cementite is impossible for practical carbon ranges and would be extremely brittle. Common Pitfalls: Mixing up proeutectoid phases; assuming similar behaviour on both sides of the eutectoid composition. Final Answer: Cementite and pearlite

Question 3

Steelmaking refining — Bessemer variants: Evaluate the statement: “In steelmaking, both phosphorus and sulphur can be removed by using the basic Bessemer (Thomas) process.”

Accepted Answer

Introduction / Context: Impurity control (P and S) is central to steel quality. Historic steelmaking routes include acid and basic Bessemer (Thomas) converters, open-hearth, and today’s basic oxygen and electric furnace processes. Knowing which route removes which impurity avoids misconceptions in metallurgy exams and shop practice. Given Data / Assumptions: Process considered: basic Bessemer (Thomas) using basic lining and basic slag. Goal: simultaneous removal of phosphorus and sulphur. Standard slag chemistry constraints apply. Concept / Approach: The basic Bessemer (Thomas) process excels at removing phosphorus because the basic slag readily ties up P as stable phosphates at high basicity and suitable temperature. However, sulphur removal in oxidising steelmaking converters is poor; effective desulphurisation generally requires a high-basicity, low-oxygen environment (often outside the converter or in secondary metallurgy) and reducing conditions with desulphurising agents (e.g., CaO, CaC2, Mg). Consequently, the blanket claim that both P and S are removed in the Thomas process is incorrect. Step-by-Step Solution: Identify what basic slag removes effectively: phosphorus.Recognise sulphur behaviour: prefers metal phase under oxidising conditions; desulphurisation is inefficient in the converter blow.Conclude only P is reliably removed; S is not.Therefore, the statement is incorrect. Verification / Alternative check: Steelmaking references show modern low-S steels rely on ladle refining/desulphurisation rather than converter blowing alone. Why Other Options Are Wrong: Adding oxygen or ferromanganese does not convert the process into an efficient desulphuriser. Carbon level does not reverse the fundamental sulphur thermodynamics in oxidising slags. Common Pitfalls: Assuming “basic = removes everything”; overlooking the opposite sulphur partitioning behaviour under oxidising conditions. Final Answer: Incorrect

Question 4

Metallography basics: By which method is the micro-structure of a metallic specimen generally examined after proper surface preparation and etching?

Accepted Answer

Introduction / Context: Metallography reveals grain size, phases, and defects that govern a metal’s properties. Routine quality control and failure analysis often begin with optical examination of polished and etched samples to interpret processing history and heat treatment response. Given Data / Assumptions: Specimen has been mounted, ground, polished, and properly etched. Goal: typical, widely used method for micro-structural observation. We distinguish micro-structure imaging from crystallographic or bulk-NDT methods. Concept / Approach: An optical microscope (metallurgical microscope) provides magnifications up to roughly 1000× with reflected light, sufficient to resolve grains, pearlite lamellae spacing (coarsely), and distributions of phases/inclusions. X-ray techniques such as XRD identify crystal structure and texture but do not directly “image” micro-structures in real space at the scale needed for routine metallography. NDT methods like ultrasonics image internal flaws rather than surface micro-constituents. The naked eye cannot resolve true micro-structural features. Step-by-Step Solution: Define “micro-structure” as features resolvable at 50–1000×.Match method: optical microscopy with reflected illumination.Eliminate techniques aimed at crystallography (XRD) or bulk defects (UT).Choose “optical microscope”. Verification / Alternative check: Standard metallography texts begin with optical methods before advancing to SEM/TEM for finer scales. Why Other Options Are Wrong: Naked eye lacks required resolution. X-ray techniques characterise phases and lattice parameters, not real-space micrographs at micrometre scale. Ultrasonic testing is for internal defect detection and thickness gauging. “None” is invalid because optical microscopy is correct and standard. Common Pitfalls: Assuming SEM is always required; in many cases, optical microscopy suffices and is more accessible. Final Answer: optical microscope

Question 5

Steel deoxidation terminology: “Killed steels” are best described as steels that are __________.

Accepted Answer

Introduction / Context: Deoxidation practice during steelmaking strongly influences casting soundness and segregation. Terms like “rimmed,” “killed,” and “semi-killed” describe the extent of deoxidation and the resulting solidification behaviour in ingots and continuous casting. Given Data / Assumptions: “Killed steel” implies strong deoxidation with agents such as aluminium or silicon. We focus on dissolved oxygen behaviour at the time of solidification. Impurity elements (P, S) are treated separately from oxygen control. Concept / Approach: Killed steels are thoroughly deoxidised so that there is negligible dissolved oxygen left to evolve CO during solidification. As a result, they solidify quietly (hence “killed”), producing uniform ingots free from gas porosity characteristic of rimmed steels. While killed steels can be made by various primary routes (BOF, EAF), the term describes deoxidation state, not the furnace type. It also does not imply near-zero phosphorus and sulphur; those are controlled by refining and secondary metallurgy, not by deoxidation alone. Step-by-Step Solution: Identify defining feature: full deoxidation → negligible dissolved oxygen.Link effect: quiet solidification with fewer gas-related defects.Reject misconceptions tying the term to specific furnace routes or P/S levels.Choose “are free from oxygen” as the best descriptive option. Verification / Alternative check: Steelmaking references consistently define killed steels as fully deoxidised (Al-killed, Si-killed). Why Other Options Are Wrong: Minimum impurity level is vague and not definitive. L-D process can produce any deoxidation level; it is not synonymous with “killed.” Near-zero P/S is not guaranteed by deoxidation alone. High gas content is the opposite of killed practice. Common Pitfalls: Equating “killed” with “clean of all impurities”; ignoring that it specifically addresses oxygen and boiling during solidification. Final Answer: are free from oxygen

Question 6

Eutectoid composition identification: A plain carbon steel containing 0.8% carbon and having a 100% pearlitic microstructure is termed as:

Accepted Answer

Introduction / Context: The eutectoid composition in the Fe–C system is a cornerstone concept in steel metallurgy. At this point, austenite transforms completely to pearlite upon slow cooling, delivering a characteristic lamellar ferrite–cementite structure and a useful balance of strength and ductility. Given Data / Assumptions: Carbon content: approximately 0.8% (textbook eutectoid for plain carbon steel). Microstructure after slow cooling: 100% pearlite. No alloying elements altering the eutectoid composition. Concept / Approach: At the eutectoid composition, austenite decomposes isothermally at the eutectoid temperature to form pearlite entirely. Steels below 0.8% C are termed hypo-eutectoid and show ferrite + pearlite; steels above 0.8% C are hyper-eutectoid and show pearlite + proeutectoid cementite. Therefore, a 0.8% C steel with 100% pearlite is properly called eutectoid steel. Step-by-Step Solution: Confirm composition at the eutectoid point (~0.8% C).Note complete transformation of austenite to pearlite on slow cooling.Classify steel accordingly as “eutectoid”.Select “eutectoid steel”. Verification / Alternative check: Fe–C phase diagram and metallography texts consistently describe 0.8% C steel as eutectoid with fully pearlitic structure at equilibrium. Why Other Options Are Wrong: Hypo-eutectoid indicates C < 0.8% with ferrite + pearlite. Hyper-eutectoid indicates C > 0.8% with pearlite + cementite network. “None of these” and “martensitic steel” do not match equilibrium slow-cooling behaviour. Common Pitfalls: Confusing eutectic (liquid reaction) with eutectoid (solid-state reaction); assuming heat treatment other than slow cooling. Final Answer: eutectoid steel

Question 7

Alloying effects in steels When vanadium is added to steel as a microalloying element, which of the following effects is most characteristic under typical engineering practice?

Accepted Answer

Introduction / Context: Vanadium is a common microalloying addition in carbon and low-alloy steels. Even in small amounts, it forms extremely fine, stable carbides and nitrides that refine grain size and strengthen the steel. Understanding this effect is essential for selecting steels for structural members, springs, and high-strength fasteners. Given Data / Assumptions: Vanadium is present in small additions (typically 0.05% to 0.20%). Strengthening mechanisms include precipitation hardening and grain refinement. Normal industrial heat treatments or controlled-rolling practices are assumed. Concept / Approach: Vanadium promotes the formation of very fine V(C,N) particles. These particles pin dislocations (precipitation strengthening) and inhibit austenite grain growth (grain refinement). Both mechanisms increase yield and ultimate tensile strength without excessively compromising ductility when properly processed. While transformation temperatures can be influenced slightly, the signature, widely observed effect is an increase in strength and improved toughness/grain control. Step-by-Step Solution: Recognize vanadium's role: forms fine vanadium carbides/nitrides V(C,N).Link to strengthening: precipitation strengthens the matrix; grain refinement raises strength per Hall–Petch relation.Draw the practical conclusion: steels with vanadium show higher tensile and yield strengths at a given carbon level.Therefore, the best choice is “increases tensile strength”. Verification / Alternative check: Specification sheets for microalloyed (HSLA) steels list vanadium-bearing grades with elevated yield strengths compared to plain-carbon controls at similar carbon levels, confirming the strengthening effect. Why Other Options Are Wrong: Decreasing tensile strength contradicts well-established microalloy practice; large shifts of critical temperature are not the primary, defining effect; claims about lowering hardenability or having no grain-size effect are inaccurate—vanadium refines grains and often improves hardenability response. Common Pitfalls: Confusing vanadium's role with elements like nickel (toughness) or molybdenum (creep/hot strength). Also, over-alloying or incorrect heat treatment can mask benefits, but under proper processing vanadium strengthens steel. Final Answer: increases tensile strength

Question 8

Plain-carbon steel classification by carbon percentage A steel containing 0.8% to 1.5% carbon is classified as which category in standard engineering terminology?

Accepted Answer

Introduction / Context: Carbon content is the primary factor used to classify plain-carbon steels because it controls achievable hardness, strength, and response to heat treatment. Correct classification is essential for selecting materials for springs, tools, and wear-resistant parts versus ductile, easily formed components. Given Data / Assumptions: Carbon range under consideration: 0.8% to 1.5% C. No significant alloying additions are implied. Standard nomenclature bands are applied. Concept / Approach: Conventional ranges are: dead-mild (≤ 0.15% C), mild/low-carbon (≈ 0.15%–0.30% C), medium-carbon (≈ 0.30%–0.60% C), and high-carbon (≈ 0.60%–1.0%+ C). Steels in the 0.8%–1.5% range are squarely within the high-carbon category and can achieve high hardness after quenching and tempering, suitable for springs, knives, and wear parts. Above about 1.0% C, brittleness increases and special processing is often required. Step-by-Step Solution: Map the given carbon range to standard categories.0.8%–1.5% C corresponds to high-carbon steels.Therefore select “high carbon steel”. Verification / Alternative check: Handbooks and standards list typical uses (springs, high-strength wires, cutting tools) for steels within 0.6%–1.0%+ C, confirming the “high carbon” designation. Why Other Options Are Wrong: Mild/dead-mild and medium-carbon steels have substantially lower carbon; “low-alloy steel” refers to deliberately alloyed compositions and is not a carbon-percentage class by itself. Common Pitfalls: Assuming “mild steel” covers all non-alloy steels; in engineering practice “mild” is low carbon, not high carbon. Final Answer: high carbon steel

Question 9

Nodularising additives in cast iron Adding magnesium to molten cast iron primarily increases which property after solidification due to the formation of spheroidal graphite?

Accepted Answer

Introduction / Context: Magnesium (and sometimes cerium) is used to treat molten cast iron to convert flake graphite into spheroidal (nodular) graphite, producing ductile iron. Recognizing the property changes stemming from this microstructural transformation is key in foundry practice and mechanical design. Given Data / Assumptions: Small additions of Mg are made to liquid iron prior to casting. Resulting material is ductile (nodular) iron, not grey (flake) iron. Matrix conditions (ferritic, pearlitic) can be adjusted by heat treatment. Concept / Approach: In grey iron, flake graphite acts as sharp stress concentrators, drastically reducing tensile strength and ductility. Mg treatment rounds the graphite into nodules, minimizing stress concentration and enabling significant increases in elongation and tensile strength. Hardness may vary depending on the matrix but does not inherently increase simply because of Mg; the hallmark change is much-improved ductility with useful strength in tension. Step-by-Step Solution: Add Mg to molten iron to modify graphite morphology.Graphite becomes spheroidal; stress concentration is reduced.Measured properties show higher tensile strength and much greater elongation compared with grey iron.Hence, “ductility and strength in tension” increases. Verification / Alternative check: Tensile test data for ferritic ductile iron commonly show elongations of 10%–20%+ versus near-zero for grey iron; ultimate strength also rises markedly. Why Other Options Are Wrong: Hardness is matrix-dependent; corrosion resistance and creep strength are not the principal improvements from Mg modification; thermal conductivity tends to decrease compared with grey iron due to nodular graphite morphology. Common Pitfalls: Confusing nodular iron with white iron; Mg does not drive carbide formation but controls graphite shape. Final Answer: ductility and strength in tension

Question 10

Polymerisation chemistry — role of catalysts Evaluate the statement: “Catalysts are used to accelerate the chemical reaction during the polymerisation of plastics.”

Accepted Answer

Introduction / Context: Polymerisation converts monomers into long-chain macromolecules. In both addition and condensation mechanisms, catalysts (or initiators) are widely used to increase reaction rates, control stereochemistry, and set molecular weight distributions, which directly affect the properties of the final plastic. Given Data / Assumptions: Catalysts speed up the rate of chemical reactions by providing alternative pathways with lower activation energy. Initiators (e.g., peroxides) are sometimes distinguished from true catalysts but serve to start and accelerate chain reactions. Industrial polymerisation seeks efficient rates at controlled temperatures and pressures. Concept / Approach: In addition polymerisation, Ziegler–Natta, metallocene, and Phillips catalysts enable stereoregularity and high rates in olefin polymerisation. In condensation polymerisation (e.g., polyesters), catalysts such as antimony, titanium, or tin compounds accelerate esterification/transesterification steps. Therefore, asserting that catalysts accelerate polymerisation is broadly correct across common plastic manufacturing routes. Step-by-Step Solution: Identify polymerisation type (addition or condensation).Associate typical catalysts/initiators with each process.Explain rate effect: lower activation energy or radical generation increases reaction rate.Conclude that the statement is true. Verification / Alternative check: Industrial practice shows dramatically higher productivities and better control using catalysts; without them, many polymerisations would be uneconomical or yield inferior materials. Why Other Options Are Wrong: Limiting the truth to only one mechanism ignores broad usage; claiming catalysts only control molecular weight is incorrect—rate enhancement is a core function. Common Pitfalls: Conflating “catalyst” and “initiator”; both can accelerate the overall polymerisation rate, though their roles differ. Final Answer: True

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