Question 1

Nickel Alloys — Composition of Monel Metal Identify the nominal composition of Monel metal among the following choices.

Accepted Answer

Introduction / Context: Monel is the trade name for a family of nickel–copper alloys renowned for seawater corrosion resistance, good strength, and excellent toughness over a wide temperature range. Recognising Monel's composition helps distinguish it from other nickel alloys like Inconel (Ni–Cr–Fe) and Incoloy (Ni–Fe–Cr), which serve different applications. Given Data / Assumptions: We compare approximate, nominal compositions as typically quoted in handbooks. Minor additions (iron, manganese, silicon, etc.) may be present in small amounts. We focus on the classic Monel 400-type chemistry. Concept / Approach: Monel alloys are primarily nickel and copper. A typical nominal composition for Monel 400 is roughly 67–70% Ni, 28–34% Cu, balance minor elements. Therefore, the option with 68% nickel, 29% copper, and about 3% other elements correctly represents Monel. Options rich in chromium are characteristic of Inconel or stainless-like nickel alloys, not Monel. Step-by-Step Solution: Identify Ni–Cu pair as the signature of Monel.Match approximate percentages: ~68% Ni and ~29% Cu aligns with Monel 400.Eliminate Ni–Cr and Ni–Fe–Cr compositions as non-Monel families. Verification / Alternative check: Commercial datasheets for Monel 400 list Ni about 63–70% and Cu about 28–34%, confirming the selected option. Why Other Options Are Wrong: Ni–Cr or Ni–Cr–Fe mixtures are Inconel/Incoloy types, not Monel.50% Ni–50% Fe corresponds to a different alloy family (permalloys), not Monel. Common Pitfalls: Assuming all high-nickel alloys are interchangeable; chemistry dictates corrosion resistance and high-temperature performance. Final Answer: 68% nickel, 29% copper and 3% other constituents

Question 2

Indian Standards — Meaning of Cast Iron Grade FG 150 According to Indian Standard designations, what does 'FG 150' signify for a cast iron?

Accepted Answer

Introduction / Context: Standardised grade designations allow engineers to select materials confidently. In Indian Standards (IS) for grey cast iron, the designation “FG” denotes “Flake Graphite,” followed by a number indicating mechanical performance. Given Data / Assumptions: We refer to grey cast iron grading under older/common IS conventions (FG grades). The numeric suffix represents a specific mechanical property value. Units are megapascals (MPa) for tensile strength unless otherwise noted. Concept / Approach: “FG 150” indicates a grey cast iron where the minimum specified tensile strength is 150 MPa. The “FG” prefix identifies grey iron (flake graphite microstructure). BHN (Brinell hardness number) is not encoded in this grade name, nor are compressive or yield strengths implied by the numeric suffix. Step-by-Step Solution: Decode “FG”: Flake Graphite → grey cast iron.Interpret “150”: minimum tensile strength = 150 MPa.Eliminate options interpreting the number as BHN or compressive strength.Select the option that pairs grey iron with 150 MPa tensile strength. Verification / Alternative check: IS conventions and many textbooks explicitly list FG 150, FG 200, etc., with the number indicating minimum tensile strength in MPa. Why Other Options Are Wrong: BHN links hardness, not tensile grade naming.White or malleable irons use different designations; “FG” is specific to grey irons. Common Pitfalls: Confusing hardness numbers with strength grades; they are specified separately. Final Answer: grey cast iron with 150 MPa as the minimum tensile strength

Question 3

Iron Ores for Pig Iron — Most Common Feed to the Blast Furnace Which iron ore is most widely used for the production of pig iron in blast furnaces?

Accepted Answer

Introduction / Context: Pig iron is produced in a blast furnace by reducing iron oxides with coke. The choice of ore affects fuel rate, slag volume, and furnace productivity. Understanding common ore feeds is foundational in ironmaking. Given Data / Assumptions: Commercial-scale blast furnace ironmaking is considered. Ores are compared by abundance, ease of beneficiation, and suitability for agglomeration. We assume standard fluxes and coke are available. Concept / Approach: Haematite (Fe2O3) is the most widely used ore for pig iron because of its abundance, high iron content, and favorable properties during sintering or pelletizing. While magnetite is also important (often oxidised to hematite during pelletizing), hematite has historically dominated as sinter/pellet feed in many regions. Step-by-Step Solution: List major ores: hematite, magnetite, limonite/goethite, siderite.Evaluate industrial usage: hematite is extensively mined and processed into sinter/pellets.Select haematite (Fe2O3) as the most common BF feedstock. Verification / Alternative check: Industry data and textbooks consistently identify hematite-rich ores as principal BF raw materials globally. Why Other Options Are Wrong: Magnetite requires additional oxidation energy if used directly; it is used but not as universally as hematite.Limonite/goethite have high combined water; they are used regionally but less favored.Siderite is less common and requires calcination to remove CO2. Common Pitfalls: Assuming local mining trends apply globally; the question seeks the general, textbook-level answer. Final Answer: haematite (Fe2O3)

Question 4

Alloy Additions — Do Sulphur, Lead, and Phosphorus Increase Steel Hardness? State whether the statement “Hardness of steel is increased by adding sulphur, lead and phosphorus” is correct in general engineering practice.

Accepted Answer

Introduction / Context: Minor additions like sulphur (S), lead (Pb), and phosphorus (P) are often used in specific steels, but their main roles differ from classic hardness-raising alloying elements such as carbon, chromium, or molybdenum. Understanding what each element does prevents design and processing mistakes. Given Data / Assumptions: The statement claims a general increase in hardness due to S, Pb, and P. We consider typical low-to-medium carbon steels used for machining and structural purposes. Heat treatment state is not specially optimized for hardness. Concept / Approach: S and Pb are primarily added to improve machinability. Sulphur combines with manganese to form MnS inclusions that break chips and reduce built-up edge; lead acts as a solid lubricant in free-machining steels. Phosphorus can raise strength and yield slightly via solution strengthening, but it severely reduces toughness and ductility; it is often kept low except in rephosphorised sheet grades. None of these elements is deliberately added mainly to raise hardness; carbon content, quenchability, and carbide-forming alloying elements control hardness far more effectively. Step-by-Step Solution: Assess roles: S/Pb → machinability; P → strength increase with embrittlement risk.Connect to hardness: marginal or adverse effects on overall hardness; not a primary hardening strategy.Conclude the general claim is false. Verification / Alternative check: Handbooks show free-machining steels have similar base hardness to comparable carbon steels unless heat-treated; improvements are in machinability, not inherent hardness. Why Other Options Are Wrong: “Yes” overstates their influence; S and Pb especially do not raise hardness.Conditions like “only for tool steels” or “only after quench” misattribute effects; tool steel hardness depends on C and carbide formers (Cr, Mo, V, W). Common Pitfalls: Confusing machinability improvements with hardness gains; they are distinct metrics. Final Answer: No

Question 5

Crystal Structures — Counting Atoms in the HCP Unit Cell How many atoms are effectively contained in a conventional close-packed hexagonal (HCP) unit cell, and where are they located?

Accepted Answer

Introduction / Context: The hexagonal close-packed (HCP) structure is one of the two classic close-packed metal crystal structures (the other is FCC). Correctly counting the number of atoms per unit cell is essential for deriving density, slip system counts, and understanding anisotropy in HCP metals like magnesium, titanium, and zinc. Given Data / Assumptions: We use the conventional hexagonal unit cell for HCP (not the smaller primitive cell). Atoms at corners and faces are shared among neighboring cells; their fractional contributions must be accounted for. Atomic hard-sphere model is assumed. Concept / Approach: In the conventional HCP cell, the atom accounting is: 12 corner atoms of the hexagon (each shared by 6 cells) contribute 12 * (1/6) = 2 atoms; 2 atoms at the centers of the top and bottom hexagonal faces (each shared by 2 cells) contribute 2 * (1/2) = 1 atom; and there are 3 atoms entirely inside the unit cell. Total = 2 + 1 + 3 = 6 atoms. This is consistent with the close-packed stacking ABAB… in HCP and the known APF of 0.74. Step-by-Step Solution: Identify all lattice positions in the conventional HCP cell.Compute contributions: corners (1/6 each) → 2 atoms.Add face-center atoms (1/2 each) → 1 atom.Include interior atoms (fully contained) → 3 atoms.Sum contributions: 2 + 1 + 3 = 6 atoms per unit cell. Verification / Alternative check: Cross-check density derivations for Mg or Ti using Z = 6; results align with published densities when lattice parameters and atomic masses are used. Why Other Options Are Wrong: Options (a) and (c) describe cubic cells (BCC and FCC features), not HCP.Option (b) ignores interior atoms and miscounts sharing, yielding the wrong total.Option (e) refers to a primitive lattice with one atom; the conventional HCP cell contains six atoms. Common Pitfalls: Mixing up “conventional” versus “primitive” cells; HCP conventional cell has six atoms even though the lattice can be described with a smaller primitive cell. Final Answer: six atoms: 12 corner atoms of the hexagon contributing 2 total, 2 face-centre atoms contributing 1 total, and 3 atoms wholly inside the cell

Question 6

Case Hardening — Definition of Carburising Carburising is the process of inducing carbon into which category of carbon steels in order to produce a hard, wear-resistant surface (case)?

Accepted Answer

Introduction / Context: Carburising is a classic case-hardening process used to achieve a hard, wear-resistant surface while maintaining a tough, ductile core. It is widely applied to gears, shafts, and pins that require surface durability with core toughness to resist shock and bending. Given Data / Assumptions: Base material is plain carbon steel before treatment. Objective is to increase surface carbon content for subsequent quench hardening. Core should remain relatively low in carbon to retain toughness. Concept / Approach: Carburising introduces carbon into the surface of low-carbon steels (typically around 0.1–0.25% C) by exposing them to a carbon-rich environment at austenitising temperatures. After diffusion increases surface carbon to about 0.8–1.0% or as specified, the part is quenched so that the high-carbon surface transforms to hard martensite, while the low-carbon core transforms to a tougher, lower-hardness structure. This gradient yields the desired combination of wear resistance and impact toughness. Step-by-Step Solution: Select a low-carbon steel substrate (e.g., 0.15% C).Heat in a carbonaceous atmosphere (solid, liquid, or gas carburising) at austenitising temperatures.Allow carbon to diffuse inward for the required case depth.Quench to form martensite in the carbon-enriched case; temper as needed. Verification / Alternative check: Design handbooks specify low-carbon case-hardening grades (e.g., 16MnCr5, 20MnCr5, 8620) explicitly for carburising. Why Other Options Are Wrong: Medium/high/ultra-high carbon steels already have sufficient carbon for through-hardening; carburising them is unnecessary and can cause excessive brittleness.Cast iron is not the standard substrate for carburising in case-hardening practice. Common Pitfalls: Confusing carburising with carbonitriding or nitriding; carburising specifically increases carbon content, not nitrogen alone. Final Answer: low

Question 7

Admiralty gun metal — identify the standard composition In non-ferrous alloy practice, “Admiralty gun metal” is a well-known copper–tin–zinc alloy used for corrosion-resistant marine fittings and bearings. Which of the following compositions best re…

Accepted Answer

Introduction / Context: Admiralty gun metal is a classic bearing and marine-service bronze. It is prized for good castability, resistance to dezincification in seawater, and reasonable strength with anti-friction properties. Recognizing its composition helps engineers select suitable alloys for pump bodies, valve seats, and condenser components where corrosion resistance and sliding performance matter. Given Data / Assumptions: All options list nominal compositions in percent by mass. “Admiralty gun metal” refers to the traditional Cu–Sn–Zn bronze used in marine service. The application context is corrosion-prone (e.g., brine, seawater). Concept / Approach: Gun metals are essentially tin bronzes with a small addition of zinc to improve fluidity and strength while maintaining corrosion resistance. Admiralty gun metal is typically around copper 88%, tin 10%, and zinc 2%. This tin level distinguishes it from brasses (Cu–Zn) and from silicon bronzes, and the small zinc content separates it from nearly binary tin bronzes. Step-by-Step Solution: Identify the family: gun metal → tin bronze with minor zinc.Select the composition close to Cu 88%, Sn 10%, Zn 2%.Reject alternatives that are brasses (high Zn), silicon bronzes, or manganese bronzes. Verification / Alternative check: Materials handbooks and marine standards cite Admiralty gun metal near 88Cu–10Sn–2Zn, sometimes with trace Pb for machinability in specific grades. Why Other Options Are Wrong: 60Cu–35Zn–5Mn: a manganese brass, not a tin bronze. 76Cu–20Si–4Zn: silicon level is unrealistic; silicon bronzes use ~3% Si, not 20%. 82Cu–12Zn–6Mn: again a manganese brass variant. 70Cu–20Sn–10Zn: much higher tin; not the standard Admiralty grade. Common Pitfalls: Confusing brasses (Cu–Zn) with bronzes (Cu–Sn); assuming “Admiralty” implies high zinc like naval brass (which is different: Cu–Zn with small Sn). Final Answer: 88% copper, 10% tin and 2% zinc

Question 8

Aluminium metallurgy — effect of manganese additions on corrosion behavior Consider the statement: “Adding manganese to aluminium improves its corrosion resistance.” Evaluate this statement for general wrought and cast aluminium alloys used in engin…

Accepted Answer

Introduction / Context: Corrosion resistance of aluminium alloys depends strongly on alloying additions and microstructure. Designers must know which elements hurt or help passivity (oxide stability) to choose the right alloy for marine, architectural, and chemical environments. The role of manganese (Mn) is often misunderstood compared with elements like magnesium, silicon, copper, zinc, and chromium. Given Data / Assumptions: General engineering aluminium alloys (cast and wrought) are considered. Surface is in typical atmospheric or aqueous environments, not specially inhibited. We assess overall corrosion behavior, not solely pitting in a specific alloy. Concept / Approach: Manganese is primarily a strength and workability modifier; it forms dispersoids that control recrystallization and can tie up iron as intermetallics, refining grain structure. Its direct effect on corrosion is minor and not broadly “improving.” In contrast, copper additions generally reduce corrosion resistance; magnesium and silicon (as Mg2Si in 6xxx) offer good corrosion-mechanical balance; chromium and zirconium can refine grain structure and sometimes improve resistance. Therefore a blanket claim that Mn improves corrosion resistance is inaccurate. Step-by-Step Solution: Identify Mn’s principal role: dispersoid former, recrystallization control, modest solid solution strengthening.Compare with elements that actually drive corrosion behavior (Cu detrimental; Mg/Si/Cr more favorable in many systems).Conclude the general statement “Mn improves corrosion resistance” is not correct. Verification / Alternative check: Datasheets for 3xxx series (Al–Mn) show corrosion performance similar to commercially pure aluminium, with the main benefits being formability and moderate strength; there is no universal increase in corrosion resistance solely due to Mn. Why Other Options Are Wrong: “Only true in high-Cu alloys” or “above 5% Mn”: not standard practice; high Mn contents are uncommon and do not universally improve corrosion. “True for castings but not wrought”: not supported as a general rule. Common Pitfalls: Assuming any third element that refines structure automatically improves corrosion; ignoring the dominant negative role of copper in many Al alloys. Final Answer: Incorrect

Question 9

Chilled cast iron — identify the correct production method In foundry practice, how is “chilled cast iron” typically produced to obtain a very hard, wear-resistant white iron surface layer?

Accepted Answer

Introduction / Context: “Chilled” surfaces on cast iron components such as rolls or wear plates are produced to resist abrasion. Controlling solidification rate and heat extraction can shift the microstructure from graphitic (gray) to cementite-rich (white) near the surface, greatly increasing hardness while the core remains tougher. Given Data / Assumptions: Objective: create a hard, white iron skin on selected regions. Material: cast iron with carbon and silicon typical of gray iron. Process variable: cooling rate at the mold–metal interface. Concept / Approach: Rapid heat extraction at the mold face suppresses graphite formation and promotes cementite (Fe3C), yielding white cast iron in the chilled zone. This is achieved by using chill inserts (metal chills) or locally thicker, more conductive mold sections. The interior cools slower and forms a gray iron matrix for damping and machinability. Step-by-Step Solution: Place metallic chills where a hard skin is required.Pour molten iron; the high cooling rate near chills favors white iron (carbide) formation.Allow slower cooling away from chills to produce gray iron core. Verification / Alternative check: Micrographs show ledeburitic/cementitic structure near chilled surfaces with hardness markedly higher than the gray core; hardness profiles drop from surface inward. Why Other Options Are Wrong: Adding magnesium: used for spheroidal graphite (ductile iron), not for chilling. Annealing white iron: produces malleable iron, not chilled surfaces. High silicon: promotes graphitisation (softer), opposite of chilling. Nitriding: a steel surface treatment, not a casting solidification method. Common Pitfalls: Confusing chilled iron with malleable or ductile iron; assuming chemistry alone dictates white/gray without considering cooling rate. Final Answer: by quick cooling (chilling) of molten cast iron

Question 10

Fe–C diagram — maximum solubility of carbon in austenite (gamma iron) Validate the statement: “The maximum solubility of carbon in austenite is 1.7% at 1130°C.” State whether it is correct or not for the iron–iron carbide system.

Accepted Answer

Introduction / Context: The iron–iron carbide (Fe–Fe3C) phase diagram is foundational in metallurgy. One key datum is the maximum solubility of carbon in austenite (gamma iron), which controls hardenability, carbon gradients during heat treatment, and the chemistry of cast irons. Given Data / Assumptions: Equilibrium (slow) conditions in the Fe–Fe3C system. Temperatures expressed in degrees Celsius. Unalloyed iron (no strong austenite stabilizers like Ni or Mn). Concept / Approach: In the Fe–Fe3C diagram, the maximum solubility of carbon in austenite occurs at the eutectic temperature around 1147°C, and the accepted value is approximately 2.11% C by mass (often rounded to 2.0–2.1%). The quoted 1.7% at 1130°C is too low and at a slightly lower temperature than the maximum-solubility point. Step-by-Step Solution: Locate the gamma phase field in the Fe–Fe3C diagram.Identify the highest C content soluble in gamma iron near 1147°C → about 2.11% C.Compare with the statement (1.7% at 1130°C) → does not match the maximum; therefore, incorrect. Verification / Alternative check: Standard diagrams and metallurgy texts consistently cite ~2.11% C at ~1147°C as the maximum solubility in austenite under equilibrium. Why Other Options Are Wrong: “Yes” contradicts accepted data. Nickel or rapid cooling qualifiers do not define the equilibrium maximum in plain Fe–C. “True at 1000°C” is also incorrect; solubility decreases as temperature drops from the maximum. Common Pitfalls: Confusing eutectoid (0.8% C at ~727°C) with maximum austenite solubility; misreading scales on phase diagrams. Final Answer: No

Question 11

German silver (nickel silver) — choose the representative composition German silver, also known as nickel silver, is a Cu–Zn–Ni alloy used for a silvery appearance without precious metal content. Which of the following nominal compositions best repr…

Accepted Answer

Introduction / Context: German silver (nickel silver) is widely used for cutlery fittings, musical instruments, and decorative hardware thanks to its bright, silvery color and good formability. Despite the name, it contains no elemental silver; the “silver” look comes from nickel in a copper–zinc matrix. Given Data / Assumptions: Compositions are given in percent by mass. The goal is to identify a typical ternary Cu–Zn–Ni formulation. No precious metal is expected in standard German silver. Concept / Approach: Nickel silver grades commonly contain 10–20% nickel; however, a number of traditional specifications use nickel around 5–10% with the remainder copper and zinc. Among the choices, only the option including ~5.35% Ni alongside ~60% Cu and ~35% Zn fits the standard “nickel silver” profile. Pure Cu–Zn brasses (without Ni) lack the characteristic silvery hue. Step-by-Step Solution: Eliminate two-component brasses (Cu–Zn without Ni).Reject any option listing silver content (not present in nickel silver).Select the ternary Cu–Zn–Ni composition: 60.45% Cu, 35.2% Zn, 5.35% Ni. Verification / Alternative check: Alloy handbooks list several nickel silver grades (e.g., CuNiZn) with nickel typically between 5–20% and no silver; the selected composition lies within this range. Why Other Options Are Wrong: Cu–Zn only: these are brasses, not nickel silvers. Option containing tin: not standard nickel silver chemistry. Option with silver: contradicts the very definition of “nickel silver.” Common Pitfalls: Assuming the trade name implies precious metal; confusing color effects of Ni with Ag plating. Final Answer: 60.45% copper, 35.2% zinc and 5.35% nickel

Question 12

Blast furnace scale — typical overall height What is the approximate overall height of a modern blast furnace used for hot metal (pig iron) production, measured from hearth to top works?

Accepted Answer

Introduction / Context: The geometric scale of a blast furnace controls residence time, burden distribution, gas–solid contact, and thermal efficiency. A sense of typical dimensions is helpful for understanding capital costs, throughput, and why burden descent and gas flow patterns matter. Given Data / Assumptions: Question asks for an approximate height, not an exact value. Conventional large furnaces are considered, not small pilot or mini blast furnaces. Height is measured from the hearth region up to the throat/top. Concept / Approach: Traditional and many modern large blast furnaces fall in the 30–35 m range for the working stack and top assembly, though some high-capacity plants may exceed this. Options of 10 m or 20 m are too small for industrial ironmaking; 40 m can occur but is above the “typical” textbook value. Therefore, 30 m is a reasonable approximation. Step-by-Step Solution: Eliminate clearly undersized options (10 m, 20 m) incompatible with industrial throughput.Recognize that 30–40 m is the common design envelope.Choose the central, most representative value: 30 m. Verification / Alternative check: Industry descriptions and plant tours frequently cite heights near 30–35 m, with total structure heights sometimes higher when including top charging equipment. Why Other Options Are Wrong: 10 m and 20 m: far below typical industrial scale. 40 m or 50 m: possible in some designs but not the standard “approximate” figure taught in fundamentals courses. Common Pitfalls: Confusing furnace shell height with total building height; mixing up blast furnaces with smaller cupolas used in foundries. Final Answer: 30 m

Question 13

Surface hardening methods — identify the case hardening family Which of the following heat treatment processes are classified as case hardening methods used to harden the surface while maintaining a tougher core?

Accepted Answer

Introduction / Context: Case hardening creates a hard, wear-resistant surface layer (case) over a tougher, ductile core. It is crucial in gears, camshafts, and shafts where surface fatigue and wear dominate while impact resistance must be preserved in the core. Given Data / Assumptions: Steel components requiring surface hardness and core toughness. Diffusional thermochemical processes considered. Objective: compare carburising, cyaniding, nitriding. Concept / Approach: Carburising enriches the surface with carbon at elevated temperatures, followed by quenching to form martensite in the case. Cyaniding introduces carbon and nitrogen from cyanide salts for a thin, hard case at lower times. Nitriding diffuses nitrogen at lower temperatures (typically 500–550°C), forming hard nitrides without quenching, with excellent dimensional control. All three are standard case hardening processes. (Note: induction hardening is a surface-hardening method but not a thermochemical “case” process; it relies on selective austenitisation and quenching.) Step-by-Step Solution: Recognize carburising: carbon diffusion + quench → hard case.Recognize cyaniding: C + N diffusion from cyanide bath.Recognize nitriding: N diffusion producing nitride case without quench.Therefore, all listed processes belong to case hardening. Verification / Alternative check: Heat-treatment texts group carburising, cyaniding, and nitriding under thermochemical case hardening methods. Why Other Options Are Wrong: Any single selection ignores the others which also satisfy the definition. “Induction hardening only” is not a thermochemical case but a thermal surface-hardening technique; it is not among the given three. Common Pitfalls: Conflating case hardening (diffusion) with surface hardening (thermal) processes; assuming quench is always required (nitriding is not). Final Answer: all of these

Question 14

Grain size effects in steels — properties of fine-grained steel Which statement best describes the typical mechanical behavior of fine-grained steel, including its tendency to distort during heat treatment?

Accepted Answer

Introduction / Context: Prior-austenite grain size (and resulting ferrite/pearlite packet size) strongly affects strength, ductility, and toughness. Fine grains increase grain boundary area, which impedes crack initiation and slip, raising toughness while aiding dimensional stability during thermal cycles. Given Data / Assumptions: Comparing fine-grained and coarse-grained steels of similar composition. Conventional heat treatments (normalizing, quenching, tempering). Distortion considered as a result of nonuniform transformation and thermal gradients. Concept / Approach: Hall–Petch behavior states yield strength increases as grain size decreases. Toughness also generally benefits because cracks are deflected or blunted by frequent boundaries. During heat treatment, finer and more uniform transformation structures reduce internal stresses and dimensional changes, lowering distortion risk compared with coarse-grained materials that transform nonuniformly and can exhibit higher residual stresses. Step-by-Step Solution: Relate fine grains to higher yield and improved toughness.Connect uniform, fine transformations to reduced distortion on heating/cooling.Select the option indicating more ductility and less tendency to distort. Verification / Alternative check: Charpy data and dimensional stability studies show improved impact energy and reduced warpage for fine-grained steels after quench and temper compared with coarse-grained equivalents. Why Other Options Are Wrong: Options suggesting “less tough” contradict well-known trends. “Greater tendency to distort” is inconsistent with finer, more uniform transformations. “Always more brittle” is incorrect; fine grains usually reduce brittleness. Common Pitfalls: Assuming higher strength always reduces ductility drastically; overlooking the role of alloy carbides and heat treatment uniformity. Final Answer: is more ductile and has a less tendency to distort during heat treatment

Question 15

Body-centred cubic (BCC) lattice — atoms per unit cell In crystallography of metals, how many atoms are effectively contained in one unit cell of a body-centred cubic (BCC) space lattice?

Accepted Answer

Introduction / Context: Unit cell atom counting is fundamental in materials science and solid-state physics. It underpins density calculations, slip system enumeration, and understanding coordination numbers and packing efficiency. For body-centred cubic (BCC) structures (e.g., alpha iron), correctly counting atoms per unit cell prevents serious property miscalculations. Given Data / Assumptions: BCC lattice has atoms at the eight cube corners and one atom at the body centre. Each corner atom is shared among eight neighboring unit cells. Counting is for the effective number of atoms wholly contained within one unit cell. Concept / Approach: Corner atoms contribute 1/8 of an atom per unit cell because each is shared by 8 cells. With 8 corners, the total contribution is 8 * (1/8) = 1 atom. The body-centre atom belongs entirely to that cell and contributes 1 atom. Adding these yields 2 atoms per unit cell. This count differs from coordination number (number of nearest neighbors), which for BCC is 8, and from the number of atoms intersecting the cell faces (zero in BCC). Step-by-Step Solution: Compute corner contribution: 8 corners * 1/8 = 1 atom.Add body-centre atom: 1 atom.Total atoms per BCC unit cell = 2 atoms. Verification / Alternative check: Using atomic packing factor (APF) for BCC, APF = (2 * 4/3 * pi * r^3) / a^3 with a = 4r / sqrt(3) confirms the standard density relationships for BCC metals. Why Other Options Are Wrong: 1 atom: ignores the body-centre atom. 4 atoms: corresponds to FCC, not BCC. 8 atoms: confuses coordination number with atoms per cell. 14 atoms: unrelated; sometimes appears in other contexts (e.g., number of atoms in certain polyhedra), not BCC atoms per cell. Common Pitfalls: Mixing “atoms per cell” with “coordination number”; forgetting to divide shared corner atoms by 8. Final Answer: 2 atoms

Question 16

Phosphor bronze — typical phosphorus content (percent by mass) Phosphor bronze is a copper–tin alloy deoxidized and strengthened by a small phosphorus addition. What is the typical phosphorus percentage present in phosphor bronze?

Accepted Answer

Introduction / Context: Phosphor bronze is widely used for springs, bearings, and electrical connectors due to its combination of strength, fatigue resistance, and good corrosion behavior. A key feature is a small phosphorus addition that refines grain structure, improves wear, and acts as a deoxidizer during melting. Given Data / Assumptions: Base alloy: copper with several percent tin. Phosphorus is a minor addition, not a major constituent. Percentage values are given as percent by mass. Concept / Approach: Phosphorus content in phosphor bronzes is typically in the hundredths to tenths of a percent range (for example, 0.03–0.35% depending on grade). Around 0.1% is a representative value found in many wrought and cast grades, sufficient to deoxidize and to form fine phosphide phases that enhance wear and stiffness without embrittlement. Much higher levels (e.g., 1% or more) would drastically change properties and are not characteristic of standard phosphor bronzes. Step-by-Step Solution: Recognize “phosphor bronze” implies a small P addition to Cu–Sn.Choose a value in the typical range: ~0.1%.Exclude unrealistic values (1%, 11.1%, 98%) that do not match standard grades. Verification / Alternative check: Alloy specifications (e.g., C51000, C52400 series) list phosphorus in the approximate 0.03–0.35% range; many common grades cluster near 0.1%. Why Other Options Are Wrong: 1%: too high for standard phosphor bronze; would embrittle and alter phases. 11.1% and 98%: clearly unrealistic for a minor alloying element. 0.01%: possible in some variants but lower than typical; 0.1% is the representative textbook figure. Common Pitfalls: Confusing tin content (several percent) with phosphorus (minor); assuming “phosphor” implies very high P content. Final Answer: 0.1

Question 17

High-speed steels (HSS) — tungsten content trend In traditional tungsten-type high-speed steels used for cutting tools, the percentage of tungsten present is generally the __________ among the principal alloying elements (compared with chromium and …

Accepted Answer

Introduction / Context: High-speed steels are engineered tool steels designed to retain high hardness at elevated temperature, a property often called red hardness. The classic tungsten series (T-grades) achieves this through a high proportion of tungsten, supported by chromium and a small amount of vanadium. Recognizing which element predominates helps learners connect composition with performance. Given Data / Assumptions: We consider traditional tungsten-based HSS grades used for drills, taps, and milling cutters. Typical comparative elements: tungsten, chromium, and vanadium. Focus is on relative proportion, not exact percentages. Concept / Approach: Tungsten forms stable carbides that confer hot hardness and wear resistance. In T-series HSS, tungsten content is large, commonly around the high-teens by percent mass. Chromium is present at a moderate level to aid hardenability and oxidation resistance. Vanadium is deliberately kept low to moderate to refine grain size and provide abrasion resistance via vanadium carbides. Therefore, among these key alloying elements, tungsten is present in the highest proportion. Step-by-Step Solution: Identify the function of each element: W for hot hardness, Cr for hardenability and oxidation resistance, V for grain refinement and wear.Recall the relative levels in classic HSS: W is highest, Cr is moderate, V is lowest.Map to the blank: the tungsten percentage is the maximum among principal additions.Select the option that matches this relationship: maximum. Verification / Alternative check: Published compositions of T-series HSS list tungsten in the neighborhood of the high-teens percentage, with chromium around several percent and vanadium near one to a few percent. This confirms the qualitative ranking. Why Other Options Are Wrong: Minimum, negligible, or zero: contradict the defining chemistry of tungsten-type HSS. Moderate: understates tungsten's dominant role in T-series grades. Common Pitfalls: Confusing tungsten-type HSS with molybdenum-type HSS; while Mo can substitute partly for W, the tungsten emphasis remains characteristic of the classic T-series. Final Answer: maximum

Question 18

Heat treatment — austempering transformation product During the austempering process (isothermal transformation of austenite at an intermediate temperature), austenite changes into which microstructure?

Accepted Answer

Introduction / Context: Austempering is a heat treatment that improves toughness and reduces distortion compared with conventional quench and temper. Instead of forming brittle martensite immediately on quenching, the steel is held isothermally so that a different microstructure develops. Knowing the correct transformation product is essential for selecting processing routes. Given Data / Assumptions: Austenitize the steel and then quench rapidly to a temperature above the martensite start temperature. Hold isothermally at this bainitic range until transformation is complete. Final properties target a good balance of strength and toughness. Concept / Approach: In austempering, the steel is quenched to a temperature where bainite, not martensite, forms isothermally. The process avoids the stresses and cracking associated with direct martensite formation and tempering. The resulting bainite can be upper or lower bainite depending on the transformation temperature, each with distinct toughness and strength characteristics. Step-by-Step Solution: Start with fully austenitized steel.Quench quickly to an intermediate bath (commonly salt bath) just above the martensite range.Hold isothermally so that austenite transforms to bainite.Cool to room temperature after completion; tempered martensite is not required because bainite already possesses tempered-like attributes. Verification / Alternative check: Time-temperature-transformation diagrams show a bainite region between pearlite and martensite; austempering uses this region to produce bainite without passing into the martensite start temperature. Why Other Options Are Wrong: Martensite: forms with rapid quench below martensite start, not during austempering holds. Troostite and sorbite: historical terms for tempered structures, not the direct product of austempering. Tempered martensite: would require forming martensite first and then tempering, which is not the austempering route. Common Pitfalls: Confusing austempering with martempering; martempering aims to reduce thermal gradients before forming martensite, whereas austempering forms bainite isothermally. Final Answer: bainite

Question 19

Nickel–chromium alloys — comparative iron content Evaluate the statement: “Nichrome contains more iron than Inconel.” Choose the correct response.

Accepted Answer

Introduction / Context: Nichrome and Inconel are both nickel-based alloy families, but they serve different purposes. Nichrome is widely used as resistance heating wire, while Inconel denotes a family of high-temperature corrosion-resistant superalloys. Comparing their typical iron contents helps clarify their roles and compositions. Given Data / Assumptions: Nichrome usually refers to Ni–Cr heater alloys, such as Nichrome 80/20 (about 80% Ni, 20% Cr) with little to no iron. Inconel grades (for example, 600) are Ni–Cr–Fe alloys containing appreciable iron, often several to about ten percent or more depending on the grade. We compare general, common grades used in practice. Concept / Approach: While compositions vary across proprietary grades, a typical Nichrome for heating elements has very low iron compared with common Inconel alloys. Inconel is formulated with intentional iron additions for metallurgical balance and cost, alongside nickel and chromium for high-temperature strength and oxidation resistance. Therefore, it is inaccurate to say Nichrome contains more iron than Inconel in the general sense. Step-by-Step Solution: Identify common Nichrome: low iron content (often near zero in 80/20).Identify common Inconel: Ni–Cr–Fe with several percent iron.Compare: typical Inconel has more iron than common Nichrome heater grades.Thus, the statement “Nichrome contains more iron than Inconel” is incorrect. Verification / Alternative check: Datasheets for Nichrome 80/20 and Inconel 600/601/625 show the qualitative trend of higher iron in Inconel than in Nichrome heater alloys. Why Other Options Are Wrong: Agree: contradicts the common compositions used industrially. Conditional options suggest exceptions, but the standard heater-grade Nichrome does not exceed Inconel in iron content. Insufficient information: general grade information is widely known and sufficient for this comparison. Common Pitfalls: Overgeneralizing across all proprietary alloys; while compositions vary, the typical Nichrome used for heating wire is not iron-rich compared to Inconel. Final Answer: Disagree

Question 20

Bessemer converter operation — meaning of the red flame During the blowing process in a Bessemer converter, the appearance of a bright red flame typically indicates that:

Accepted Answer

Introduction / Context: The Bessemer process refines molten pig iron into steel by blowing air through the bath. Observing the flame at the mouth of the converter offers real-time cues about which impurities are being oxidized. Students should correlate flame appearance with the sequence of chemical reactions. Given Data / Assumptions: Typical acid Bessemer practice on low-phosphorus iron. Common oxidation sequence: silicon and manganese first, followed by carbon. Operators monitor flame characteristics to time the blow. Concept / Approach: When air is blown, the most readily oxidized elements burn first. Silicon and manganese oxidize early, producing slags and a flame that then changes character. The bright red or luminous flame associated with carbon monoxide burning indicates that carbon oxidation has begun in earnest after Si and Mn have largely been removed. The intensity of the flame helps determine the endpoint. Step-by-Step Solution: At blow start: Si and Mn oxidize preferentially.As these diminish, carbon begins to oxidize, producing CO that burns at the mouth with a bright flame.The red or vivid flame thus signals carbon removal phase.Therefore, select the option stating Si and Mn are burned out and carbon oxidation has started. Verification / Alternative check: Classic metallurgical descriptions of converter practice correlate the flame rise and fall with the carbon removal curve, confirming the interpretation. Why Other Options Are Wrong: Air burning out silicon and manganese: this occurs earlier before the red flame surge. Immediate tilt to pour: pouring is timed after the carbon blowdown endpoint, not simply at first red flame. No red flame: contrary to observed practice. Phosphorus removal: acid Bessemer does not remove phosphorus effectively. Common Pitfalls: Confusing the initial oxidation stage with the carbon monoxide flame stage; the latter marks carbon oxidation, not Si/Mn removal. Final Answer: silicon and manganese have been removed and carbon oxidation has started

Engineering Materials Questions