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IIW IWE practice questions

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Question 1Welding processes and equipment

In submerged arc welding, what is the primary function of the granular flux blanket that covers the arc and molten weld pool?

  1. It shields the arc from the atmosphere and chemically refines the weld metal while stabilizing the arc Correct answer.
  2. It acts as a mechanical clamp that holds the two plates in alignment during welding
  3. It conducts the welding current from the contact tip to the workpiece
  4. It accelerates the cooling rate of the weld metal to refine the grain structure

Explanation

The flux in SAW melts to form a slag that excludes air, provides alloying and deoxidation reactions, and stabilizes the arc while allowing high currents. It is not a clamping device, not a current path, and it actually slows cooling by insulating the weld.

Question 2Welding processes and equipment

Which shielding gas is most commonly selected for gas metal arc welding of carbon steel in the short-circuiting transfer mode to promote stable, spatter-controlled operation?

  1. Pure argon
  2. Pure helium
  3. Carbon dioxide or a carbon dioxide-rich argon mixture Correct answer.
  4. An argon-helium 80/20 mixture

Explanation

Carbon dioxide and CO2-rich argon blends give the reactive, high-enthalpy arc needed for stable short-circuiting transfer on carbon steel and are economical. Pure argon is used for nonferrous metals, and helium-rich mixes are chosen for high heat input on thick sections.

Question 3Welding processes and equipment

What is the essential characteristic of the electrode in shielded metal arc welding that distinguishes it from a bare wire?

  1. It is made exclusively from austenitic stainless steel
  2. It carries a fusible mineral coating that generates shielding gas and slag Correct answer.
  3. It is water-cooled to prevent overheating during high-current operation
  4. It is always connected to the positive terminal regardless of polarity choice

Explanation

Covered electrodes carry a flux coating that decomposes to provide shielding gas, forms slag for protection and shape control, and adds alloying elements. The coating is the defining feature; polarity is selectable and the core wire may be many materials.

Question 4Welding processes and equipment

Which welding process operates with the workpiece connected as one electrode and a non-consumable tungsten electrode in an inert gas atmosphere, typically used for thin sheet and root passes?

  1. Flux-cored arc welding
  2. Friction stir welding
  3. Electroslag welding
  4. Gas tungsten arc welding Correct answer.

Explanation

GTAW uses a non-consumable tungsten electrode, an inert shielding gas and often a separately fed filler wire, giving precise control at low currents. FCAW and electroslag use consumable electrodes, and friction stir welding is a solid-state process without an arc.

Question 5Welding processes and equipment

In resistance spot welding, the heat required to form the nugget is generated primarily at which location?

  1. Uniformly throughout the full thickness of both sheets
  2. At the surface of the electrodes where they contact the sheet
  3. In the water cooling circuit of the electrode holders
  4. At the faying interface between the two overlapping sheets Correct answer.

Explanation

Because contact resistance is highest at the faying interface, Joule heating concentrates there and forms the nugget. Surface contact and bulk resistance also generate some heat, but the design intent is to localize melting at the interface.

Question 6Welding processes and equipment

Which power source characteristic is required for stable operation of the self-regulating gas metal arc welding process with a constant wire feed speed?

  1. A flat or slightly rising characteristic giving near-constant voltage Correct answer.
  2. A constant-current characteristic with high open-circuit voltage
  3. A pulsed output with a fixed frequency independent of wire feed
  4. A steeply drooping characteristic with near-constant current

Explanation

GMAW relies on a constant-voltage (flat) characteristic so that arc length changes produce large current changes that restore the burn-off balance. Drooping constant-current sources are used for SMAW and GTAW, not for self-regulating GMAW.

Question 7Welding processes and equipment

What is the main purpose of using a backing gas purge when welding the root of an austenitic stainless steel pipe by GTAW?

  1. To increase the arc voltage for deeper penetration
  2. To preheat the pipe to the interpass temperature
  3. To prevent oxidation and loss of corrosion resistance on the root surface Correct answer.
  4. To increase the deposition rate of the filler wire

Explanation

Trailing or backing inert gas excludes oxygen from the molten root, preventing chromium-depleted oxide scale that destroys corrosion resistance. It does not affect deposition rate, preheat or arc voltage directly.

Question 8Welding processes and equipment

Which process is classified as a solid-state welding process in which a rotating, non-consumable tool stirs the material along a seam without melting it?

  1. Plasma arc welding
  2. Submerged arc welding
  3. Electrogas welding
  4. Friction stir welding Correct answer.

Explanation

Friction stir welding joins material by severe plastic deformation and frictional heating below the melting point, using a rotating pin tool. Plasma, submerged arc and electrogas processes all involve melting.

Question 9Welding processes and equipment

A welder is depositing a multipass butt weld in 20 mm thick carbon steel with SAW and observes that the weld metal impact toughness is below specification. Which change is most likely to improve toughness without altering the joint design?

  1. Switching to a higher-current single-pass-per-layer technique
  2. Increasing the arc voltage while keeping current and travel speed constant
  3. Increasing heat input and using a larger weave to widen the bead
  4. Reducing heat input within qualified limits and controlling interpass temperature Correct answer.

Explanation

Excessive heat input coarsens the microstructure and lowers toughness, so reducing heat input and controlling interpass temperature refines grains and limits embrittling phases. Widening the weave or raising voltage further increases heat input and worsens the condition.

Question 10Welding processes and equipment

During GMAW spraying transfer on 6 mm carbon steel, the arc becomes unstable and stubbing occurs after the operator increases wire feed speed without changing the voltage setting. What is the most appropriate corrective action?

  1. Increase the voltage setting to restore arc length and burn-off balance Correct answer.
  2. Decrease the shielding gas flow rate
  3. Increase the contact-tip-to-work distance to more than 30 mm
  4. Switch the polarity to electrode negative

Explanation

Raising wire feed speed increases burn-off demand; if voltage is unchanged the arc shortens and stubbing results. Increasing voltage lengthens the arc and restores the balance between wire feed rate and burn-off rate.

Question 11Welding processes and equipment

Why is alternating current with a superimposed high-frequency unit often preferred for GTAW of aluminium?

  1. It removes the need to clean the oxide layer before welding
  2. It eliminates the need for any shielding gas
  3. It allows the tungsten electrode to be smaller than with direct current electrode negative
  4. The positive half-cycle breaks the oxide film while the negative half-cycle limits tungsten erosion Correct answer.

Explanation

Aluminium forms a tenacious oxide with a very high melting point; the electrode-positive half-cycle provides cathodic cleaning that breaks it down, while electrode-negative gives penetration and protects the tungsten. Shielding gas and pre-weld cleaning are still required.

Question 12Welding processes and equipment

In a mechanized FCAW operation, the weld shows excessive spatter, a rough bead and porosity while the parameter sheet is unchanged. Which inspection action best isolates the cause before adjusting electrical parameters?

  1. Change to a larger diameter contact tip
  2. Reduce the travel speed by 20 percent
  3. Verify wire feed rolls, liner condition and contact tip wear for smooth wire delivery Correct answer.
  4. Increase the shielding gas flow to the maximum regulator setting

Explanation

Erratic wire feed from worn rolls, a kinked liner or a worn tip creates arc instability, spatter and gas shielding loss that mimic parameter faults. Checking the wire delivery path first avoids chasing electrical settings that are actually correct.

Question 13Welding processes and equipment

Which statement correctly describes the role of electrode force in resistance spot welding?

  1. It ensures intimate contact between sheets and electrodes and forges the nugget during cooling Correct answer.
  2. It upsets the workpiece to increase the contact resistance for more heat
  3. It controls the cooling rate by conducting heat away from the weld
  4. It replaces the need for welding current in thin-gauge material

Explanation

Electrode force consolidates the interfaces so current density is uniform and, after current ceases, forges the solidifying nugget to prevent shrinkage porosity and cracking. It does not create heat and cannot replace current.

Question 14Welding processes and equipment

A fabricator must weld 25 mm thick structural steel with high deposition rate, deep penetration and no visible arc, in a shop with good fume extraction. Which process best matches these requirements?

  1. Manual metal arc welding with rutile electrodes
  2. Submerged arc welding with a multi-wire or tandem configuration Correct answer.
  3. Oxy-fuel gas welding with a multi-flame nozzle
  4. Gas tungsten arc welding with cold wire feed

Explanation

SAW gives high deposition rates, deep penetration and a covered arc suited to thick sections in a fixed shop position. Manual processes are too slow for this thickness and GTAW is limited in deposition rate.

Question 15Welding processes and equipment

What is the principal reason for using direct current electrode negative in GTAW of thin stainless steel sheet?

  1. It concentrates heat in the workpiece and minimises tungsten electrode erosion Correct answer.
  2. It provides cathodic cleaning of the surface oxide
  3. It increases the risk of tungsten spitting into the weld
  4. It removes the need for a trailing shield

Explanation

With the electrode negative, electrons bombard the workpiece, so most arc energy enters the plate while the tungsten stays relatively cool and erosion is low. Cathodic cleaning occurs in the electrode-positive half-cycle, which DCEN does not provide.

Question 16Welding processes and equipment

In electroslag welding of thick sections, what is the function of the molten slag bath?

  1. It shields the arc from the atmosphere during the arcing stage only
  2. It provides the electrical resistance that generates the heat to melt the electrode and joint faces Correct answer.
  3. It acts as a mechanical support that transmits the clamping force
  4. It cools the weld metal rapidly to refine the grain structure

Explanation

Once the process is established, current passes through the conductive slag, whose resistance generates the heat that melts the filler and the joint faces; there is no sustained arc. The slag also protects the pool but does not clamp or rapidly cool it.

Question 17Welding processes and equipment

Which technique is appropriate to reduce angular distortion when making a multipass butt weld in a thick plate?

  1. Balancing passes on each side of the joint and using backstep or skip sequencing Correct answer.
  2. Increasing the heat input for every pass to speed completion
  3. Welding continuously from one end to the other without interruption
  4. Using a single large weave pass instead of several stringer beads

Explanation

Balanced deposition and backstep or skip sequencing distribute shrinkage more evenly and limit accumulated angular distortion. High heat input, wide weaves and continuous one-direction welding all increase distortion.

Question 18Welding processes and equipment

A GTAW weld on aluminium shows a dark, smutty surface along the edges of the bead. Which cause should be investigated first?

  1. Too large a tungsten electrode diameter for the current
  2. Insufficient cleaning action from incorrect balance or polarity settings Correct answer.
  3. Excessive travel speed with too high a current
  4. Excessive argon flow through a trailing shield

Explanation

Smut on aluminium usually indicates inadequate cathodic cleaning, caused by a balance setting too far toward electrode-negative or by incorrect polarity. The other options affect bead shape or electrode life but do not produce that characteristic smut.

Question 19Welding processes and equipment

Which parameter change in SAW most directly increases penetration into the root of a square-edged butt joint?

  1. Increasing the arc voltage while keeping current and travel speed constant
  2. Increasing the travel speed while keeping current and voltage constant
  3. Increasing the welding current while keeping voltage and travel speed constant Correct answer.
  4. Increasing the flux layer depth while keeping all electrical parameters constant

Explanation

In SAW, current density controls penetration, so raising current deepens the weld while voltage mainly widens the bead. Higher voltage or travel speed reduces penetration, and flux depth affects shielding rather than penetration.

Question 20Welding processes and equipment

Why must the electrode in resistance seam welding be a rotating wheel rather than a fixed bar?

  1. To cool the workpiece by conducting heat away rapidly
  2. To eliminate the need for overlap between the sheets
  3. To increase the contact resistance by sliding over the surface
  4. To allow continuous progression of the weld along the seam while carrying current and force Correct answer.

Explanation

Roller electrodes let the workpiece advance continuously between successive current pulses, producing a series of overlapping nuggets that form a seam. Sliding would damage the surface, and overlap is still required.

Question 21Welding processes and equipment

In GMAW, what does the term 'inductance' control in the welding circuit?

  1. The frequency of the high-frequency arc starting circuit
  2. The rate of current rise and fall, which affects spatter level in short-circuiting transfer Correct answer.
  3. The shielding gas flow rate through the regulator
  4. The wire feed speed relative to the set voltage

Explanation

Inductance is the slope control that governs how quickly current rises during a short circuit and falls after it clears, which strongly influences spatter in dip transfer. It does not set gas flow, wire feed or arc-start frequency.

Question 22Welding processes and equipment

Which condition most strongly justifies preheating before welding a thick, highly restrained carbon-manganese steel joint?

  1. High carbon equivalent and thick section, which raise the risk of hydrogen-assisted cold cracking Correct answer.
  2. A requirement to increase the deposition rate
  3. Low ambient humidity in the workshop
  4. The use of a rutile electrode rather than a basic one

Explanation

Preheat slows cooling after welding, giving hydrogen time to escape and reducing the hard martensitic zones that cause cold cracking, particularly with high carbon equivalent and high restraint. Humidity and electrode type are secondary compared with the material factor.

Question 23Welding processes and equipment

In a synergic pulsed GMAW power source, what does the 'synergic' control link?

  1. Electrode polarity to the welding current
  2. Travel speed to the contact-tip-to-work distance
  3. Shielding gas composition to the arc voltage
  4. Pulse parameters to the wire feed speed so that one control adjusts the whole programme Correct answer.

Explanation

A synergic programme stores matched pulse peak current, background current and pulse frequency for each wire feed speed, so the operator sets one value and the machine maintains one-drop-per-pulse transfer. Gas composition, stick-out and polarity are separate settings.

Question 24Welding processes and equipment

A thick-section SAW joint shows solidification cracking along the centreline. Which combination of measures most directly addresses the metallurgical cause?

  1. Increasing current and voltage to widen the bead and dilute more base metal
  2. Reducing heat input, changing to a flux/filler with lower sulphur and phosphorus, and controlling bead shape Correct answer.
  3. Increasing the travel speed to reduce the number of passes
  4. Adding preheat to increase the depth-to-width ratio

Explanation

Centreline solidification cracking is driven by segregation of sulphur and phosphorus and by a deep, narrow bead shape that concentrates strain at the centre. Lower impurity levels, modified flux/filler chemistry and a wider, shallower bead reduce the risk.

Question 25Welding processes and equipment

In resistance spot welding of aluminium sheet, why is a special surface preparation and often a higher electrode force with a different electrode material required compared with steel?

  1. Aluminium has a tenacious oxide film and high thermal and electrical conductivity, so contact resistance must be controlled Correct answer.
  2. Aluminium has very high electrical resistance that causes overheating of the electrodes
  3. Aluminium is ferromagnetic, which distorts the current path
  4. Aluminium melts at a higher temperature than steel, demanding longer weld times

Explanation

The oxide film on aluminium is insulating and unstable, and the metal conducts heat and current very well, so surface conditioning and higher force with suitable electrode alloys are needed to establish a stable contact resistance and concentrate heat. Aluminium is not ferromagnetic and melts at a lower temperature than steel.

Question 26Welding processes and equipment

In the conventional oxy-fuel gas welding process, what is the primary function of the acetylene in the oxygen-acetylene flame?

  1. It supplies the combustible fuel that, when burned in oxygen, produces the flame heat and the shielding atmosphere around the molten pool. Correct answer.
  2. It controls the electrode melting rate by chemically reacting with the filler metal.
  3. It acts as a fluxing agent that dissolves oxides from the weld pool surface.
  4. It provides the shielding gas that prevents nitrogen pickup from the surrounding air.

Explanation

In oxy-acetylene welding the acetylene is the fuel gas; combustion with oxygen in the inner cone releases the heat used to melt the joint and produces the surrounding gas envelope that excludes air. It does not act as a flux or as an inert shielding gas, and it does not react chemically with the filler to set melting rate.

Question 27Welding processes and equipment

A manual metal arc (SMAW) electrode is classified with a cellulosic covering. Which combination of characteristics should the welder expect when using it on a root pass in carbon steel pipe?

  1. An arc that deposits mainly by a short-circuiting transfer mode with negligible gas evolution from the covering.
  2. A soft, low-penetration arc with a thick, easily detached slag and very low hydrogen content.
  3. A deep, forceful penetrating arc with a relatively thin, fast-freezing slag and a hydrogen-rich arc atmosphere. Correct answer.
  4. A stable arc that produces a glassy slag requiring chemical removal and a strongly oxidizing atmosphere.

Explanation

Cellulosic coverings decompose in the arc to give a high proportion of hydrogen and carbon monoxide, producing a forceful, deeply penetrating arc and a thin slag that freezes quickly, which suits vertical-down root passes. The covering is deliberately not low-hydrogen, so it requires hydrogen control measures on susceptible steels.

Question 28Welding processes and equipment

A fabricator is setting up a submerged arc welding station to weld 12 mm plate in the flat position with a single wire. Which arrangement of the process variables is consistent with good bead shape and slag release?

  1. Alternating current with the wire vertical and the lowest practicable arc voltage.
  2. Direct current electrode negative with the wire inclined strongly forwards (pushing) and maximum arc voltage.
  3. Direct current electrode positive with the wire vertical and arc voltage increased until the arc burns visibly above the flux.
  4. Direct current electrode positive with the wire inclined slightly backwards (dragging) and a moderate arc voltage. Correct answer.

Explanation

DCEP concentrates heat at the workpiece and gives good penetration, while a slight backward (drag) inclination widens the bead and helps slag detach. Arc voltage must stay low enough for the arc to remain buried under the flux; raising it until the arc is visible defeats the process.

Question 29Welding processes and equipment

In gas tungsten arc welding, a welder notices that the tungsten electrode has developed a balled, irregular tip after welding for some time on carbon steel with DCEN. Which explanation best accounts for this?

  1. The filler wire is being added too far ahead of the arc, which overheats the tungsten.
  2. The electrode is contaminated, for example by touching the pool or by using the wrong polarity, so the tip melts back irregularly. Correct answer.
  3. The shielding gas flow is too high, which cools the electrode tip unevenly.
  4. The current is too low for the electrode diameter, which causes the tip to melt.

Explanation

A properly sized thoriated or lanthanated tungsten on DCEN holds a pointed tip; a balled or irregular tip indicates contamination, accidental contact with the pool, or operation on the wrong polarity, which overheats the electrode. Current that is too low tends to cause arc instability rather than melting the tip.

Question 30Welding processes and equipment

A resistance spot welding cell is producing welds in 1.5 mm low-carbon steel sheet with a fixed electrode force and weld time. Production data show that increasing the welding current beyond a certain value causes the nugget diameter to stop growing and then to fall, with heavy electrode indentation and expulsion. Which mechanism best explains this behaviour?

  1. Excess current causes the nugget to grow until the surrounding sheet softens and the electrodes sink in, reducing the current density and allowing expulsion that ejects metal from the nugget. Correct answer.
  2. The contact resistance falls to zero at high current, so no heat can be generated in the interface.
  3. The welding transformer saturates at high current, so the secondary current actually decreases and the nugget shrinks.
  4. The electrode force rises automatically with current because of thermal expansion of the electrodes, which then suppresses nugget formation.

Explanation

Beyond the useful current range, the nugget grows and the softened sheet allows the electrodes to indent, so current density falls and molten metal is expelled, producing a smaller or defective nugget. The practical current range is therefore bounded above by expulsion and surface damage, not by transformer saturation.

Question 31Materials and their behaviour during welding

In the iron–carbon equilibrium diagram, what is the maximum solubility of carbon in ferrite (α-Fe) at room temperature?

  1. About 0.77 %
  2. About 0.008 % Correct answer.
  3. About 2.11 %
  4. About 0.02 %

Explanation

Ferrite has a body-centred cubic lattice with very limited interstitial space, so its carbon solubility falls to roughly 0.008 % at room temperature. The 0.02 % value applies at about 723 °C, the maximum solubility of carbon in ferrite.

Question 32Materials and their behaviour during welding

Which crystal lattice does austenite (γ-Fe) possess?

  1. Body-centred cubic
  2. Hexagonal close-packed
  3. Face-centred cubic Correct answer.
  4. Body-centred tetragonal

Explanation

Austenite is the face-centred cubic high-temperature modification of iron, which has a larger interstitial site and therefore dissolves far more carbon than ferrite. On cooling it transforms into ferrite, pearlite, bainite or martensite depending on the cooling rate.

Question 33Materials and their behaviour during welding

What is the typical carbon content of the eutectoid composition in plain carbon steel?

  1. 0.8 % Correct answer.
  2. 0.2 %
  3. 0.45 %
  4. 1.2 %

Explanation

The eutectoid point of the iron–carbon diagram lies at about 0.8 % C and roughly 723 °C, where austenite transforms directly into pearlite. Steels below this value are hypoeutectoid and contain proeutectoid ferrite, while those above contain proeutectoid cementite.

Question 34Materials and their behaviour during welding

Which of the following is the standard designation for a fully killed, fine-grain structural steel according to EN 10025-2?

  1. S355J2+N Correct answer.
  2. S235JRC
  3. S275AR
  4. S185

Explanation

In EN 10025-2 the symbol +N denotes normalising rolling, and the J2 quality class requires impact testing at −20 °C with a minimum of 27 J. The killed, fine-grain condition is achieved through aluminium or microalloy additions and normalising treatment.

Question 35Materials and their behaviour during welding

According to the carbon equivalent formula CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15, what CEV value generally marks the threshold above which preheat becomes advisable for arc welding of structural steels?

  1. 0.30
  2. 0.40 Correct answer.
  3. 0.20
  4. 0.60

Explanation

A carbon equivalent of about 0.40 is the widely accepted threshold above which hydrogen-assisted cold cracking risk increases and preheat should be considered. Below this value, normal structural steels can usually be welded without preheat if hydrogen and restraint are controlled.

Question 36Materials and their behaviour during welding

A steel has a carbon equivalent (CEV) of 0.48 and a plate thickness of 30 mm. What is the most appropriate measure to prevent hydrogen-assisted cold cracking?

  1. Weld with a higher current and no preheat
  2. Apply preheat and use low-hydrogen consumables Correct answer.
  3. Use cellulose-coated electrodes without preheating
  4. Increase the heat input to above 5 kJ/mm

Explanation

A CEV of 0.48 combined with 30 mm thickness places the steel in a high-hardenability regime where cold cracking is likely unless hydrogen is controlled. Preheat slows the cooling rate and allows hydrogen to diffuse out, while low-hydrogen consumables reduce the amount of hydrogen introduced.

Question 37Materials and their behaviour during welding

Which type of stainless steel is susceptible to sensitisation and intergranular corrosion after welding in the heat-affected zone?

  1. Ferritic stainless steel with very low carbon
  2. Austenitic stainless steel stabilised with titanium or niobium
  3. Duplex stainless steel with balanced ferrite and austenite
  4. Austenitic stainless steel with more than 0.03 % carbon Correct answer.

Explanation

In austenitic steels with carbon above about 0.03 %, chromium carbide precipitates on the grain boundaries in the 450–850 °C range and depletes the adjacent matrix of chromium. This chromium-depleted zone then corrodes preferentially in aggressive environments.

Question 38Materials and their behaviour during welding

Why must the ferrite content in duplex stainless steel welds be controlled within a specified range (typically 30–70 %)?

  1. To reduce the nickel content of the filler
  2. To balance corrosion resistance and toughness Correct answer.
  3. To prevent the formation of sigma phase during welding
  4. To increase the hardness of the weld metal

Explanation

Duplex stainless steels rely on a balanced two-phase microstructure to combine high strength and chloride resistance with good toughness. Too much ferrite reduces toughness and corrosion resistance, while too little ferrite promotes hot cracking and reduces strength.

Question 39Materials and their behaviour during welding

Which aluminium alloy series is generally considered non-heat-treatable and relies on solid-solution strengthening and strain hardening?

  1. 6xxx
  2. 7xxx
  3. 2xxx
  4. 5xxx Correct answer.

Explanation

The 5xxx series is based on magnesium as the main alloying element and is strengthened only by solid solution and work hardening, not by precipitation. The 2xxx, 6xxx and 7xxx series are all heat-treatable and rely on precipitation hardening.

Question 40Materials and their behaviour during welding

What is the main consequence of excessive porosity in the heat-affected zone of a 6xxx aluminium alloy weld?

  1. Reduced tensile strength and fatigue resistance Correct answer.
  2. Higher hardness in the heat-affected zone
  3. Increased thermal conductivity
  4. Improved corrosion resistance

Explanation

Porosity reduces the effective cross-section and acts as stress concentrators, lowering both tensile strength and fatigue life. In heat-treatable aluminium alloys this is compounded by softening in the heat-affected zone.

Question 41Materials and their behaviour during welding

Which of the following is the principal reason titanium and its alloys must be shielded with inert gas during welding?

  1. To avoid grain growth
  2. To increase heat input
  3. To prevent hydrogen absorption
  4. To prevent oxidation and nitrogen pick-up Correct answer.

Explanation

Titanium has a high affinity for oxygen and nitrogen at welding temperatures, and even small amounts of these elements cause severe embrittlement and discolouration. Effective inert gas shielding, often with trailing shields, is therefore essential.

Question 42Materials and their behaviour during welding

In welding of copper and copper alloys, what is the primary reason for the use of preheat?

  1. To avoid hydrogen embrittlement
  2. To compensate for high thermal conductivity Correct answer.
  3. To reduce the zinc content
  4. To prevent hot cracking

Explanation

Copper conducts heat away from the weld very rapidly, so preheat compensates for the high thermal conductivity and helps achieve adequate fusion and penetration. Without preheat, the heat is drawn into the base metal and fusion may be incomplete.

Question 43Materials and their behaviour during welding

Which of the following is a characteristic feature of cast iron that strongly influences its weldability?

  1. High ductility and low hardness
  2. Low thermal expansion coefficient
  3. Low carbon content
  4. High carbon content and low ductility Correct answer.

Explanation

Cast irons contain 2–4 % carbon, much of it as graphite or cementite, and are brittle with little ductility. Welding generates steep thermal gradients and high restraint stresses that readily produce cracking in the heat-affected zone.

Question 44Materials and their behaviour during welding

During welding of a nickel-base alloy such as Alloy 625, which mechanism is the most common cause of weld metal solidification cracking?

  1. Sigma phase formation
  2. Hydrogen-assisted cracking
  3. Formation of low-melting niobium-rich eutectics Correct answer.
  4. Chromium carbide precipitation

Explanation

In niobium-bearing nickel alloys, segregation during solidification can leave low-melting eutectics along the solidification grain boundaries. These films have little strength and rupture under thermal strain, producing solidification cracking.

Question 45Materials and their behaviour during welding

What is the effect of increasing heat input on the cooling rate and resulting microstructure in a carbon-manganese steel weld?

  1. Higher heat input increases cooling rate and forms martensite
  2. Higher heat input has no effect on cooling rate
  3. Higher heat input reduces cooling rate and produces coarser ferrite Correct answer.
  4. Higher heat input reduces grain size and increases hardness

Explanation

Higher heat input means more energy per unit length, so the weld cools more slowly. The slower cooling promotes coarser ferrite and pearlite and reduces the tendency to form hard martensite.

Question 46Materials and their behaviour during welding

Why is the heat-affected zone of a high-strength low-alloy steel often the weakest region in a welded joint?

  1. It has the lowest carbon content
  2. It is protected from oxidation
  3. It experiences thermal cycles that coarsen grains and dissolve precipitates Correct answer.
  4. It contains more ferrite than the base metal

Explanation

The heat-affected zone experiences thermal cycles that coarsen the prior austenite grains and dissolve strengthening precipitates, so it can lose strength and toughness. In some steels it also forms hard, brittle microstructures that require controlled cooling.

Question 47Materials and their behaviour during welding

What is the role of nitrogen in the shielding gas when welding austenitic stainless steel with the TIG process?

  1. It improves austenite formation and pitting resistance Correct answer.
  2. It increases the ferrite content
  3. It reduces the arc voltage
  4. It prevents chromium carbide precipitation

Explanation

Small additions of nitrogen to the shielding gas promote austenite formation and can improve pitting corrosion resistance in austenitic stainless steels. It is used in controlled amounts to balance the ferrite content, not to increase it.

Question 48Materials and their behaviour during welding

Which of the following alloying elements is a strong ferrite stabiliser and promotes the formation of sigma phase in stainless steels?

  1. Manganese
  2. Nitrogen
  3. Nickel
  4. Molybdenum Correct answer.

Explanation

Molybdenum is a strong ferrite former and, like chromium and silicon, promotes sigma phase formation during high-temperature exposure. Sigma phase is brittle and sharply reduces toughness and corrosion resistance.

Question 49Materials and their behaviour during welding

What is the effect of hydrogen in steel welds that leads to hydrogen-assisted cold cracking?

  1. It forms oxides that embrittle the grain boundaries
  2. It promotes the formation of ferrite at grain boundaries
  3. It increases the carbon equivalent of the weld metal
  4. It diffuses to regions of high stress and reduces cohesive strength Correct answer.

Explanation

Hydrogen diffuses through the lattice and collects in areas of high triaxial stress, where it lowers the cohesive strength of the metal and promotes delayed cracking. This is why hydrogen content, hardness and restraint are the three key factors in cold cracking.

Question 50Materials and their behaviour during welding

Which of the following is a typical consequence of using a very high heat input when welding a quenched and tempered high-strength steel?

  1. Softening of the heat-affected zone and loss of strength Correct answer.
  2. Increase in the yield strength of the weld metal
  3. Reduction in the width of the heat-affected zone
  4. Formation of untempered martensite in the heat-affected zone

Explanation

Excessive heat input tempers back the heat-affected zone of a quenched and tempered steel, softening it and reducing joint strength. The welding procedure must therefore limit heat input to a specified range.