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IIW IWI-S practice questions

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Question 1Welding processes and equipment

In GMAW, what is the primary function of the shielding gas?

  1. It protects the molten weld pool and electrode from atmospheric contamination Correct answer.
  2. It provides filler metal to the joint
  3. It cools the contact tip during welding
  4. It conducts the welding current to the workpiece

Explanation

The shielding gas displaces air around the arc and weld pool, preventing nitrogen and oxygen from causing porosity and embrittlement. It does not carry current, supply filler, or cool the torch tip. Gas selection and flow rate strongly influence arc stability and bead shape.

Question 2Welding processes and equipment

Which arc welding process uses a non-consumable tungsten electrode with a separate filler rod added by hand?

  1. GTAW Correct answer.
  2. SMAW
  3. SAW
  4. FCAW

Explanation

GTAW (TIG) uses a tungsten electrode that does not melt into the weld, and filler wire is added separately when needed. SMAW and FCAW use consumable electrodes that become part of the weld, and SAW is a mechanized process using granular flux.

Question 3Welding processes and equipment

What is the main purpose of the covering on a shielded metal arc welding electrode?

  1. To prevent the electrode from bending during storage
  2. To generate shielding gas and slag while stabilizing the arc Correct answer.
  3. To reduce the electrical resistance of the electrode
  4. To increase the melting rate of the core wire

Explanation

The flux coating decomposes in the arc to produce shielding gas and a protective slag, and it contains arc stabilizers and alloying elements. These functions protect the weld metal and improve bead quality. The coating is not designed to raise melting rate, lower resistance, or add stiffness.

Question 4Welding processes and equipment

Which power source characteristic is normally required for manual metal arc welding with covered electrodes?

  1. A frequency-converter square wave with no slope control
  2. A pulsed constant voltage output
  3. A constant current (drooping) characteristic Correct answer.
  4. A constant voltage characteristic with a steeply rising slope

Explanation

Manual welding needs a drooping or constant current characteristic so that arc length variations produce only small current changes, giving a stable arc. Constant voltage is used for processes with self-regulating wire feed such as GMAW. Square wave and pulsed outputs are features of specialized power sources, not a general requirement.

Question 5Welding processes and equipment

In SAW, what is the role of the granular flux layer?

  1. It provides the mechanical backing for the root pass
  2. It shields the arc, stabilizes it, and forms a slag that protects the weld Correct answer.
  3. It acts as a conductor between the wire and the workpiece
  4. It cools the wire electrode before it enters the arc

Explanation

Submerged arc welding buries the arc under granular flux that melts to form gas and slag, protecting the weld from the atmosphere and supporting arc stability. Alloying elements can also be transferred from the flux. The flux is not a current path, a wire cooler, or a mechanical backing.

Question 6Welding processes and equipment

What does the term 'duty cycle' mean for a welding power source?

  1. The fraction of total weld length made in the flat position
  2. The number of starts and stops the machine can perform per hour
  3. The ratio of arc voltage to open-circuit voltage
  4. The percentage of time in a ten-minute period that the source can operate at rated current Correct answer.

Explanation

Duty cycle is expressed as the percentage of a ten-minute period during which the power source can deliver its rated current without overheating. A 60% duty cycle means six minutes of welding followed by four minutes of cooling at rated output. It is a thermal rating, not a voltage ratio or position limitation.

Question 7Welding processes and equipment

A welder must join thin sheet steel with minimal distortion and no slag removal. Which process is most suitable?

  1. SAW with a high deposition rate
  2. FCAW with self-shielded wire
  3. SMAW with a rutile electrode
  4. GTAW with DCEN Correct answer.

Explanation

GTAW with direct current electrode negative gives a stable, low-heat-input arc suited to thin sheet, and it produces no slag because no flux is used. SMAW and FCAW generate slag that must be removed, while SAW is intended for thicker sections and higher deposition.

Question 8Welding processes and equipment

Which gas mixture is commonly used for GMAW of carbon steel in the short-circuiting transfer mode to improve arc stability?

  1. Argon with 2% oxygen
  2. Pure helium
  3. Pure nitrogen
  4. Argon with 15 to 25% carbon dioxide Correct answer.

Explanation

Argon-carbon dioxide mixtures, typically 15 to 25% CO2, provide good arc stability and penetration in short-circuiting transfer on carbon steel. Pure helium is costly and used for special applications, nitrogen is not a standard shielding gas for steel, and low-oxygen mixtures are more typical for stainless or spray transfer.

Question 9Welding processes and equipment

What is the principal advantage of the short-circuiting transfer mode in GMAW?

  1. It gives the deepest penetration of all transfer modes
  2. It allows welding of thin sections in all positions with low heat input Correct answer.
  3. It produces a completely spatter-free weld
  4. It eliminates the need for shielding gas

Explanation

Short-circuiting transfer operates at low current and voltage, so the arc is short and heat input is low, making it suitable for thin material and out-of-position work. Penetration is relatively shallow, shielding gas is still required, and some spatter is normal.

Question 10Welding processes and equipment

Which polarity is normally used for GTAW of aluminum to obtain oxide cleaning action?

  1. Direct current electrode negative
  2. Direct current electrode positive
  3. Pulsed direct current electrode negative
  4. Alternating current Correct answer.

Explanation

Alternating current alternates between electrode-negative, which gives good penetration with low tungsten heating, and electrode-positive, which provides the cathodic cleaning that breaks up the aluminum oxide film. DCEN alone gives poor cleaning, and DCEP alone would overheat the tungsten.

Question 11Welding processes and equipment

What is the main reason for using a backing gas when welding stainless steel pipe?

  1. To reduce the amount of filler metal required
  2. To speed up the solidification of the weld pool
  3. To increase the welding current capacity of the torch
  4. To prevent oxidation and loss of corrosion resistance on the root side Correct answer.

Explanation

The root side of a stainless steel weld is exposed to air and can oxidize, forming heat tint and reducing corrosion resistance. A backing or purge gas such as argon displaces air to keep the root clean. It does not affect current capacity, solidification rate, or filler consumption.

Question 12Welding processes and equipment

In FCAW, what distinguishes a self-shielded wire from a gas-shielded wire?

  1. The self-shielded wire uses a tungsten electrode inside the sheath
  2. The self-shielded wire contains fluxing ingredients that generate shielding gas without an external supply Correct answer.
  3. The self-shielded wire requires a higher flow rate of argon
  4. The self-shielded wire operates only with direct current electrode positive

Explanation

Self-shielded flux-cored wires contain ingredients in the core that decompose to provide shielding, so no external gas cylinder is needed. This makes them useful in windy field conditions. Gas-shielded wires require an external gas supply, and neither type uses a tungsten electrode.

Question 13Welding processes and equipment

What is the purpose of a wire feed drive roll with a knurled surface in GMAW?

  1. To preheat the wire before it enters the contact tip
  2. To improve grip on the wire and prevent slipping Correct answer.
  3. To straighten the wire before it reaches the arc
  4. To measure the wire feed speed electronically

Explanation

Knurled drive rolls increase friction and grip on the wire, reducing slip and feeding problems, especially with softer or flux-cored wires. They do not preheat, straighten, or measure the wire. Excessive knurling can damage some wires, so roll selection must match the wire type.

Question 14Welding processes and equipment

Which phenomenon can occur when the shielding gas flow rate in GMAW is set too high?

  1. Turbulence that aspirates air into the arc Correct answer.
  2. Complete loss of the arc
  3. Increased penetration depth
  4. Automatic reduction of the welding current

Explanation

Excessive gas flow creates turbulence that can draw surrounding air into the shielding envelope, causing porosity despite a high flow reading. Correct flow rates depend on nozzle size and conditions. High flow does not increase penetration, extinguish the arc, or change current automatically.

Question 15Welding processes and equipment

What is the function of the contact tip in a GMAW torch?

  1. It cools the weld pool after the arc passes
  2. It meters the shielding gas flow
  3. It transfers welding current to the wire electrode close to the arc Correct answer.
  4. It holds the tungsten electrode in alignment

Explanation

The contact tip is a conductive copper-alloy component that contacts the wire and transfers welding current to it just before the arc. Its bore size and condition affect arc stability and wire feeding. It does not meter gas, hold a tungsten electrode, or cool the weld pool.

Question 16Welding processes and equipment

In plasma arc welding, what is the function of the constricting orifice?

  1. It supplies additional filler metal to the weld
  2. It prevents the formation of a keyhole
  3. It reduces the open-circuit voltage of the power source
  4. It increases the arc column temperature and energy density Correct answer.

Explanation

The constricting orifice forces the arc through a narrow opening, raising current density and temperature and producing a stiff, high-energy-density plasma jet. This enables keyhole welding of thicker sections. The orifice does not alter open-circuit voltage, feed filler, or suppress keyhole formation.

Question 17Welding processes and equipment

Which of the following best describes electroslag welding?

  1. A solid-state process using friction between two workpieces
  2. A laser process using a filler wire and coaxial gas
  3. An arc-based process using a consumable electrode and shielding gas
  4. A resistance process in which molten slag provides heat to fuse the joint Correct answer.

Explanation

Electroslag welding uses the electrical resistance of a molten slag bath to generate heat, melting the electrode and joint faces without a sustained arc. It is a high-deposition process for thick vertical sections. It is not an arc process, a solid-state friction process, or a laser process.

Question 18Welding processes and equipment

Why is stud welding with a ceramic ferrule used in structural applications?

  1. The ferrule supplies the welding current to the stud
  2. The ferrule cools the stud immediately after welding
  3. The ferrule concentrates the arc and contains the molten metal to form a sound weld collar Correct answer.
  4. The ferrule replaces the need for a power source

Explanation

The ceramic ferrule surrounds the stud during stud welding, confining the arc and retaining the molten metal so a sound fillet collar forms. It also shields the molten zone from air. It does not conduct current, replace the power source, or provide cooling.

Question 19Welding processes and equipment

In resistance spot welding, what does the term 'nugget' refer to?

  1. The clamping force applied by the electrode
  2. The oxide film on the sheet surface
  3. The copper electrode cap that contacts the sheet
  4. The fused zone at the sheet interface formed by resistance heating Correct answer.

Explanation

The nugget is the cast, fused zone created at the interface of the sheets by resistance heating and forging pressure. Its size and shape determine weld strength. Electrode caps, surface oxides, and clamping force are separate elements of the process.

Question 20Welding processes and equipment

Which electrode angle and technique are recommended for a vertical-up root pass in SMAW to control penetration?

  1. A slight drag angle with a fast travel speed
  2. A perpendicular or slight drag angle with a short arc and controlled weave Correct answer.
  3. A slight push angle with a long arc and high current
  4. A 45-degree push angle with maximum current

Explanation

For vertical-up root passes, a short arc with a slight drag or perpendicular angle and controlled manipulation helps control penetration and prevent burn-through. Long arcs and excessive current increase the risk of defects. Push angles and maximum current are not appropriate for root control.

Question 21Welding processes and equipment

What is the main effect of increasing the arc voltage in GMAW while keeping wire feed speed constant?

  1. A lower current with a more convex bead
  2. A narrower bead with deeper penetration
  3. A wider, flatter bead with less penetration Correct answer.
  4. A higher deposition rate with no change in bead shape

Explanation

Increasing arc voltage lengthens the arc, spreading the arc force over a wider area and producing a flatter, wider bead with reduced penetration. If voltage is excessive, undercut and spatter can result. Current and deposition are governed mainly by wire feed speed.

Question 22Welding processes and equipment

Why must the electrode in a resistance welding machine be water-cooled?

  1. To prevent overheating of the copper electrodes and maintain consistent weld quality Correct answer.
  2. To supply cooling to the workpiece after welding
  3. To increase the electrical resistance of the electrode
  4. To reduce the clamping force required

Explanation

Copper electrodes carry high currents and would overheat without internal water cooling, which would degrade their properties and weld consistency. Cooling helps maintain electrode life and stable nugget formation. It does not intentionally raise resistance, cool the workpiece, or reduce clamping force.

Question 23Welding processes and equipment

A GTAW welder observes that the tungsten electrode is eroding rapidly and contaminating the weld. Which cause is most likely when welding aluminum?

  1. Using a gas lens with a low flow rate
  2. Using direct current electrode positive Correct answer.
  3. Using alternating current with too little electrode-positive half-cycle
  4. Using a thoriated tungsten electrode

Explanation

Direct current electrode positive concentrates heat on the tungsten, causing rapid melting and contamination of the weld. For aluminum, alternating current is normally used to balance penetration and cleaning while protecting the electrode. Thoriated electrodes and low gas flow do not cause this specific rapid erosion pattern.

Question 24Welding processes and equipment

Which combination of parameters is most likely to produce a keyhole in plasma arc welding of a thick section?

  1. Low current, high travel speed, and a large orifice
  2. High shielding gas flow with a large standoff distance
  3. Low plasma gas flow with a wide orifice
  4. High current density from a constricted arc with a suitable backing Correct answer.

Explanation

Keyhole plasma welding requires a constricted, high-current-density arc that penetrates through the workpiece, with a backing or support to control the root. Low current or a wide orifice would not produce a keyhole. Gas flow and standoff affect stability but are not the primary drivers.

Question 25Materials and their behaviour during welding

In the iron-carbon equilibrium diagram, what is the maximum carbon content of austenite (γ-Fe) that can exist in solid solution?

  1. 6.67 %
  2. 0.77 %
  3. 2.11 % Correct answer.
  4. 4.30 %

Explanation

Austenite has an FCC lattice and can dissolve up to about 2.11 % carbon at 1147 °C, which is the composition of the eutectic austenite boundary. Above this carbon level, cementite forms as a separate phase rather than dissolving in the austenite.

Question 26Materials and their behaviour during welding

Which lattice structure does ferrite (α-Fe) possess at room temperature, and what is its practical consequence for welding?

  1. Body-centred tetragonal, giving very high hardness
  2. Body-centred cubic, giving limited carbon solubility and moderate strength Correct answer.
  3. Hexagonal close-packed, giving poor toughness at low temperature
  4. Face-centred cubic, giving high ductility and low strength

Explanation

Ferrite is body-centred cubic and dissolves only about 0.02 % carbon at room temperature, so excess carbon must be present as carbides. This low solubility and the BCC slip behaviour explain the moderate strength and good toughness of ferritic weld metal.

Question 27Materials and their behaviour during welding

A steel contains 0.45 % carbon and is slowly cooled from the austenite region. Which microstructural constituents are expected at room temperature?

  1. Bainite and retained austenite
  2. Cementite and ledeburite
  3. Austenite and martensite
  4. Ferrite and pearlite Correct answer.

Explanation

Hypoeutectoid steels with carbon between 0.02 % and 0.77 % precipitate proeutectoid ferrite from austenite before the eutectoid reaction, and the remaining austenite transforms to pearlite. The result at slow cooling is a mixture of ferrite and pearlite.

Question 28Materials and their behaviour during welding

What is the main metallurgical reason that carbon equivalent (CE) formulas such as the IIW equation are used when welding steels?

  1. To calculate the exact tensile strength of the deposited weld metal
  2. To estimate the oxidation loss of alloying elements in the arc
  3. To determine the required preheat for austenitic stainless steels
  4. To predict the risk of hydrogen-assisted cold cracking from hardenability Correct answer.

Explanation

The carbon equivalent converts the hardening effect of alloying elements into an equivalent carbon content, so it indicates the hardenability of the heat-affected zone. Higher CE means a greater tendency to form hard martensite and therefore a higher risk of cold cracking, which drives preheat decisions.

Question 29Materials and their behaviour during welding

Which of the following is the characteristic effect of increasing the cooling rate on the heat-affected zone of a hardenable carbon-manganese steel?

  1. Formation of coarse ferrite with lower hardness
  2. Complete dissolution of all carbides with no hardness change
  3. Formation of martensite with increased hardness and cracking risk Correct answer.
  4. Transformation of the structure into stable austenite at room temperature

Explanation

Fast cooling suppresses diffusion-controlled transformation to ferrite and pearlite, so austenite transforms to martensite, which is hard and brittle. In the HAZ this raises hardness and, combined with hydrogen and restraint, increases susceptibility to cold cracking.

Question 30Materials and their behaviour during welding

Which statement correctly describes the difference between the terms 'weld metal' and 'heat-affected zone'?

  1. Weld metal and the HAZ are identical regions described by different standards
  2. Weld metal is always the parent plate, while the HAZ is the filler deposit
  3. Weld metal is unaffected by the thermal cycle, while the HAZ is fully melted
  4. Weld metal has been melted and solidified, while the HAZ was heated in the solid state without melting Correct answer.

Explanation

The weld metal is the portion that reached the liquid state and solidified from the melt, so it has a cast, often dendritic structure. The HAZ is parent metal that experienced a thermal cycle hot enough to change microstructure but never melted.

Question 31Materials and their behaviour during welding

Why does nitrogen pick-up from the atmosphere cause porosity and embrittlement in ferritic steel weld metal?

  1. Nitrogen lowers the melting point of the steel below the arc temperature
  2. Nitrogen reacts with the slag to produce hydrogen gas
  3. Nitrogen increases the carbon content of the weld metal
  4. Nitrogen forms brittle nitrides and has low solubility in ferrite at low temperature Correct answer.

Explanation

Nitrogen has much lower solubility in solid ferrite than in the liquid, so excess nitrogen is rejected during solidification and can form porosity. Nitrogen also forms hard nitrides and promotes strain ageing and loss of toughness.

Question 32Materials and their behaviour during welding

Which of the following best explains why hydrogen is particularly damaging in high-strength steel welds?

  1. Hydrogen increases the fluidity of the molten pool and improves penetration
  2. Hydrogen combines with carbon to form graphite flakes in the weld
  3. Hydrogen diffuses into the lattice and accumulates in stressed regions, causing delayed cracking Correct answer.
  4. Hydrogen raises the transformation temperature of austenite

Explanation

Hydrogen dissolved in the weld metal diffuses through the lattice and collects at stress concentrations such as the HAZ root, where it promotes delayed cold cracking. The risk increases with higher strength and hardness because these steels tolerate less hydrogen.

Question 33Materials and their behaviour during welding

Which alloying element is primarily responsible for the excellent corrosion resistance of austenitic stainless steel?

  1. Chromium Correct answer.
  2. Carbon
  3. Nickel
  4. Molybdenum

Explanation

Chromium forms a thin, adherent passive oxide film on the surface that protects the steel from corrosion. A chromium content of at least about 10.5 % is the basis of stainless behaviour, and nickel stabilises austenite rather than providing the passive film.

Question 34Materials and their behaviour during welding

What is sensitisation of an austenitic stainless steel and what is its consequence?

  1. Dissolution of the passive film by welding current, causing arc blow
  2. Formation of martensite at the surface, causing hardening and cracking
  3. Absorption of nitrogen into the austenite, causing porosity
  4. Chromium carbide precipitation at grain boundaries, leaving chromium-depleted zones prone to intergranular corrosion Correct answer.

Explanation

In the range of roughly 450 to 850 °C, chromium carbides precipitate at grain boundaries and consume chromium from the adjacent zones. Those depleted regions lose their passivity and become anodic, so intergranular corrosion can occur in service or during pickling.

Question 35Materials and their behaviour during welding

Which low-temperature transformation product is formed when austenite is cooled very rapidly in a hardenable steel?

  1. Coarse pearlite
  2. Spheroidite
  3. Primary ferrite
  4. Martensite Correct answer.

Explanation

Very rapid cooling prevents carbon diffusion, so the FCC austenite transforms by a shear mechanism into body-centred tetragonal martensite. The trapped carbon distorts the lattice and produces high hardness with limited ductility.

Question 36Materials and their behaviour during welding

A weld is made on a C-Mn steel with a carbon equivalent of 0.42. What is the most appropriate practical measure to reduce the risk of cold cracking?

  1. Apply a suitable preheat and control hydrogen input Correct answer.
  2. Reduce the interpass temperature to below ambient
  3. Use a higher-carbon filler to match the base metal
  4. Increase the cooling rate by quenching immediately after welding

Explanation

A CE of 0.42 indicates significant hardenability, so a preheat slows the cooling rate and gives hydrogen time to escape. Controlling hydrogen at source through dry consumables and clean surfaces complements the preheat.

Question 37Materials and their behaviour during welding

What is the principal reason for limiting heat input when welding quenched and tempered high-strength steels?

  1. To prevent excessive softening and loss of strength in the HAZ Correct answer.
  2. To reduce the arc voltage below the open-circuit voltage
  3. To increase the carbon content of the weld metal
  4. To prevent the formation of coarse ferrite in the weld metal

Explanation

Excessive heat input tempers the HAZ of quenched and tempered steels, reducing hardness and strength below the design values. Manufacturers therefore specify both a minimum heat input to avoid hard martensite and a maximum to avoid over-tempering.

Question 38Materials and their behaviour during welding

Which solidification mode in austenitic stainless steel weld metal is preferred to reduce solidification cracking?

  1. Fully austenitic solidification
  2. Eutectic solidification with continuous grain-boundary films
  3. Fully ferritic solidification with no austenite
  4. Primary ferrite with austenite, giving a ferrite content of a few percent Correct answer.

Explanation

A small amount of delta ferrite in the as-welded structure disrupts continuous solidification grain boundaries and dissolves harmful impurities such as sulphur and phosphorus. This is why filler metals such as 308L are designed to deposit a few percent ferrite.

Question 39Materials and their behaviour during welding

Which of the following is a typical consequence of excessive sulphur and phosphorus in steel weld metal?

  1. Increased susceptibility to solidification cracking Correct answer.
  2. Increased resistance to hydrogen cracking
  3. Improved toughness and ductility
  4. Complete suppression of porosity

Explanation

Sulphur and phosphorus are impurity elements that segregate to solidification grain boundaries and form low-melting films. These films cannot accommodate shrinkage strains, so hot cracking occurs during solidification.

Question 40Materials and their behaviour during welding

Why is the aluminium content of fully killed steel relevant to welding?

  1. Aluminium raises the sulphur content of the weld metal
  2. Aluminium increases the carbon equivalent and the risk of cold cracking
  3. Aluminium forms a low-melting film that causes hot cracking
  4. Aluminium refines grain size and combines with nitrogen, reducing strain ageing and porosity Correct answer.

Explanation

Aluminium is used for deoxidation and grain refinement, and it ties up nitrogen as aluminium nitride, which reduces strain ageing and nitrogen porosity. This is why fine-grained, fully killed structural steels behave more predictably in the HAZ.

Question 41Materials and their behaviour during welding

What is the effect of a coarse prior-austenite grain size in the HAZ on toughness?

  1. It increases toughness by promoting fine ferrite
  2. It reduces toughness because coarse grains provide fewer barriers to crack propagation Correct answer.
  3. It improves toughness by reducing the number of grain boundaries
  4. It has no effect on toughness in ferritic steels

Explanation

Grain boundaries act as barriers to cleavage crack propagation, so a coarser prior-austenite grain size means fewer barriers and a larger effective crack path. The result is a higher ductile-to-brittle transition temperature and reduced toughness.

Question 42Materials and their behaviour during welding

Which statement about the effect of nickel in steel is correct?

  1. Nickel forms a passive oxide film that gives corrosion resistance
  2. Nickel promotes the formation of ferrite and raises the ductile-to-brittle transition temperature
  3. Nickel increases the sulphur content and promotes hot cracking
  4. Nickel stabilises austenite and improves low-temperature toughness Correct answer.

Explanation

Nickel is an austenite stabiliser that lowers the transformation temperatures and improves toughness, which is why it is used in low-temperature steels and in austenitic stainless steels. It does not provide the passive film, which depends on chromium.

Question 43Materials and their behaviour during welding

During welding of a high-carbon (0.8 %) steel, why must a high preheat and careful procedure be used?

  1. The steel melts at a lower temperature and requires a shorter arc
  2. The HAZ is prone to forming hard martensite and cracking, so slow cooling and hydrogen control are needed Correct answer.
  3. The carbon will evaporate and change the composition of the joint
  4. The weld metal will be fully austenitic at room temperature and must be stabilised

Explanation

High-carbon steels have high hardenability, so the HAZ readily transforms to hard martensite even at moderate cooling rates. Preheat, controlled heat input and low-hydrogen consumables reduce the cracking risk and allow hydrogen to escape.

Question 44Materials and their behaviour during welding

Which of the following correctly describes the difference between the austenite-to-ferrite transformation and the austenite-to-martensite transformation?

  1. Ferrite forms by diffusion, while martensite forms by a diffusionless shear mechanism Correct answer.
  2. Neither transformation involves a change in crystal structure
  3. Both are diffusion-controlled and depend on time at temperature
  4. Ferrite forms by a shear mechanism, while martensite forms by long-range diffusion

Explanation

Ferrite formation requires carbon to diffuse away from the growing ferrite, so it is time and temperature dependent. Martensite forms without carbon diffusion, by a coordinated shear of the lattice, which is why it can form even during rapid quenching.

Question 45Materials and their behaviour during welding

In the context of the iron-carbon diagram, what is the significance of the eutectoid composition of 0.77 % carbon?

  1. It is the carbon content of cementite
  2. It is the maximum carbon solubility in ferrite
  3. It is the composition of the eutectic in cast iron
  4. It is the composition at which austenite transforms directly into pearlite at the lowest temperature of the eutectoid reaction Correct answer.

Explanation

At 0.77 % carbon, austenite transforms isothermally into the lamellar ferrite-cementite aggregate known as pearlite at the eutectoid temperature. Steels with less carbon contain proeutectoid ferrite, and those with more contain proeutectoid cementite.

Question 46Materials and their behaviour during welding

Which mechanism best explains why austenitic stainless steel weld metal can suffer from hot cracking when the ferrite content is too low?

  1. Low ferrite increases the hydrogen content of the weld metal
  2. Low ferrite causes the weld metal to transform to martensite on cooling
  3. Low ferrite allows continuous austenite grain boundaries with low-melting impurity films that cannot accommodate shrinkage strain Correct answer.
  4. Low ferrite raises the melting point of the grain boundaries above the bulk metal

Explanation

Without a few percent of delta ferrite, solidification produces continuous austenite boundaries where sulphur and phosphorus segregate as low-melting films. During the final stage of solidification, shrinkage strains tear these weakened boundaries and hot cracks form.

Question 47Materials and their behaviour during welding

Which of the following statements about the effect of manganese in steel welding is correct?

  1. Manganese forms a passive oxide film that protects against corrosion
  2. Manganese is added to increase the carbon content of the weld metal
  3. Manganese combines with sulphur to form manganese sulphide and improves toughness Correct answer.
  4. Manganese stabilises ferrite and lowers hardenability

Explanation

Manganese is a deoxidiser and sulphur scavenger, forming manganese sulphide instead of low-melting iron sulphide films. This reduces hot cracking susceptibility and improves toughness, and manganese also contributes to hardenability.

Question 48Materials and their behaviour during welding

A procedure qualification requires that the HAZ hardness of a C-Mn steel weld not exceed 350 HV10. Which combination of measures is most directly aimed at meeting this requirement?

  1. Applying sufficient preheat and controlling heat input to slow the cooling rate Correct answer.
  2. Welding with a higher hydrogen potential to promote tempering
  3. Using a higher-carbon filler metal to match the base metal
  4. Increasing the cooling rate by reducing preheat and heat input

Explanation

Hardness in the HAZ is governed by the cooling rate through the transformation range and by the steel's hardenability. Adequate preheat and controlled heat input slow the cooling, allowing softer transformation products and lowering the maximum hardness.

Question 49Construction and design

In a welded steel structure subject to fatigue loading, which detail category assignment is governed primarily by the geometric stress concentration at the weld toe rather than by the static tensile strength of the base metal?

  1. The Charpy impact energy of the base metal
  2. The yield strength specified for the base plate
  3. The through-thickness tensile property of the plate
  4. The fatigue detail category from the applicable design code Correct answer.

Explanation

Fatigue detail categories in structural codes are derived from the geometry of the joint, weld toe angle, and presence of defects, not from base metal static strength. Two steels of different yield strength but identical weld detail share essentially the same fatigue category. Impact energy and through-thickness properties govern other limit states entirely.

Question 50Construction and design

A designer must specify a full-penetration butt weld in a 25 mm thick plate that will be ultrasonically tested over its full length. Which weld quality level and inspection requirement is normally stated on the drawing to achieve this?

  1. Partial penetration with visual examination only
  2. Partial penetration with dye penetrant testing of the root
  3. Full penetration with 100 percent volumetric examination and an agreed acceptance level Correct answer.
  4. Full penetration with visual examination and no volumetric testing

Explanation

Full-penetration welds in thick plate carrying fatigue or severe service demand volumetric examination, usually ultrasonic or radiographic, over the full length. The drawing should state the extent of testing and the acceptance level referenced to the applicable standard. Partial penetration or visual-only inspection would not demonstrate internal soundness.