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IIW IWP practice questions

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Question 1Welding processes and equipment

In shielded metal arc welding (SMAW), what is the primary function of the electrode coating (flux covering)?

  1. It generates shielding gas and slag to protect the molten weld metal Correct answer.
  2. It acts as a permanent backing to support the weld root
  3. It cools the weld pool rapidly to refine the grain structure
  4. It conducts the welding current more efficiently than the core wire

Explanation

The covering decomposes under the arc to produce shielding gas and forms a slag layer that protects the molten metal from atmospheric contamination. It also stabilises the arc and can add alloying elements. Current is carried by the core wire, not the coating.

Question 2Welding processes and equipment

Which shielding gas is most commonly used for gas metal arc welding (GMAW) of carbon steel in the short-circuiting transfer mode?

  1. Pure helium
  2. Pure oxygen
  3. Argon with 20% hydrogen
  4. Carbon dioxide or an argon-CO2 mixture Correct answer.

Explanation

CO2 or argon-CO2 mixtures provide good arc stability and penetration for short-circuiting transfer on carbon steel at economical cost. Pure helium is used mainly for high-heat-input applications such as aluminium or copper. Hydrogen-bearing mixtures are avoided on carbon steel because of porosity and cracking risk.

Question 3Welding processes and equipment

In gas tungsten arc welding (GTAW), what is the role of the tungsten electrode?

  1. It melts and becomes part of the weld deposit
  2. It provides the shielding gas through its porous structure
  3. It supplies the filler metal to the joint
  4. It carries the current and sustains the arc without being consumed Correct answer.

Explanation

The tungsten electrode is a non-consumable electrode that maintains the arc; filler, when required, is added separately. Tungsten's very high melting point allows it to survive the arc heat. Shielding gas is supplied externally through the torch nozzle.

Question 4Welding processes and equipment

What distinguishes the spray transfer mode in GMAW from short-circuiting transfer?

  1. The electrode touches the pool and extinguishes the arc each cycle
  2. The arc is pulsed off for most of each cycle to reduce heat
  3. Metal is transferred as fine droplets across an open arc at high current density Correct answer.
  4. Transfer occurs only when the electrode is dipped in flux

Explanation

Spray transfer uses high current density above a transition value so that fine droplets detach and cross an open arc without short circuits. It gives high deposition and deep penetration but is normally limited to flat or horizontal positions. Short-circuiting transfer, by contrast, relies on repeated contact with the pool.

Question 5Welding processes and equipment

Which power source characteristic is required for manual metal arc welding with rutile electrodes to maintain a stable arc as arc length varies?

  1. A rising characteristic with increasing current
  2. A steeply drooping (constant current) characteristic Correct answer.
  3. A perfectly flat (constant voltage) characteristic
  4. A characteristic independent of arc voltage

Explanation

A drooping characteristic gives approximately constant current over a range of arc voltages, so the welder can vary arc length without large current swings. This stabilises the manual process. Constant-voltage sources are used for continuous wire processes with self-regulating arcs.

Question 6Welding processes and equipment

What is the main purpose of adding a small percentage of oxygen to argon shielding gas in GMAW of austenitic stainless steel?

  1. To prevent any oxidation of the weld surface
  2. To increase the ferrite content beyond 50%
  3. To eliminate all spatter
  4. To improve arc stability and weld bead wetting Correct answer.

Explanation

Small oxygen or CO2 additions to argon improve arc stability, droplet transfer, and bead shape (wetting) on stainless steel. The addition must stay low to avoid excessive oxidation and loss of corrosion resistance. It does not eliminate spatter entirely.

Question 7Welding processes and equipment

In submerged arc welding (SAW), the granular flux performs which combined function?

  1. It cools the workpiece by conduction through the copper backing
  2. It replaces the need for any welding current return path
  3. It shields the arc and melt, and the fused flux forms a slag that protects and shapes the bead Correct answer.
  4. It acts as a consumable electrode carrying the current

Explanation

In SAW the arc is buried under a layer of granular flux that excludes air and melts into slag covering the bead. The slag protects the solidifying metal and influences bead shape. The electrode is a separate bare wire, and current return still requires a work connection.

Question 8Welding processes and equipment

Which welding process is best suited to joining thick aluminium plate with high deposition and no flux residue, using an inert gas shield?

  1. Oxy-fuel welding with a carburising flame
  2. SMAW with rutile electrodes
  3. GMAW with argon shielding Correct answer.
  4. Manual metal arc with cellulosic electrodes

Explanation

GMAW with argon (often argon-helium) gives good cleaning action, high deposition, and no flux residue on aluminium. Aluminium's oxide layer and high conductivity make flux-based manual processes unsuitable. Argon provides stable transfer for aluminium.

Question 9Welding processes and equipment

What is the effect of increasing the electrode extension (stick-out) in GMAW with constant voltage?

  1. Arc voltage rises sharply and the arc extinguishes
  2. Welding current decreases because of resistive heating in the extended wire Correct answer.
  3. Shielding gas flow increases automatically
  4. Welding current increases and penetration deepens

Explanation

Longer stick-out increases the resistive (I2R) heating of the wire, which raises the burn-off rate and, with a constant-voltage source, reduces the current. This reduces penetration and can cause lack of fusion. The welder must therefore keep stick-out consistent.

Question 10Welding processes and equipment

In oxy-acetylene welding, which flame type is used for welding steels to avoid carbon pickup and excess oxidation?

  1. A pure acetylene flame with no oxygen
  2. A strongly oxidising flame with excess oxygen
  3. A strongly carburising flame with an excess acetylene feather
  4. A neutral flame with equal oxygen and acetylene Correct answer.

Explanation

A neutral flame has approximately equal oxygen and acetylene and is the standard choice for steel, giving neither carbon pickup nor excess oxidation. Carburising flames add carbon, while oxidising flames cause scaling and decarburisation. Pure acetylene cannot sustain the required combustion.

Question 11Welding processes and equipment

Which feature distinguishes plasma arc welding (PAW) from GTAW when keyhole technique is used on thicker plate?

  1. The process uses a consumable flux-cored wire
  2. Shielding gas is replaced by a vacuum
  3. The electrode touches the workpiece to start each pass
  4. The constricted arc produces high energy density that can penetrate fully and form a keyhole Correct answer.

Explanation

A constricting nozzle raises the energy density of the plasma arc, allowing a keyhole to form through the plate that closes behind the weld. GTAW is normally limited to shallower penetration in a single pass. The process still uses a non-consumable electrode and inert shielding.

Question 12Welding processes and equipment

What is the primary reason for using alternating current (AC) when GTAW welding aluminium?

  1. It eliminates the need for any shielding gas
  2. It produces a purely spray transfer of filler metal
  3. It allows the use of a consumable tungsten electrode
  4. The electrode-positive half-cycle breaks up the oxide film while the electrode-negative half-cycle limits heat to the tungsten Correct answer.

Explanation

On AC, the electrode-positive portion provides cathodic cleaning that breaks the refractory aluminium oxide, while the electrode-negative portion carries most of the heat into the work and protects the tungsten. This balance makes AC standard for aluminium GTAW. DC electrode-negative alone gives poor oxide removal.

Question 13Welding processes and equipment

Which defect is most directly associated with insufficient shielding gas flow during GMAW?

  1. Wagon tracks along the bead edges
  2. Porosity from atmospheric contamination Correct answer.
  3. Transverse cracking from hydrogen
  4. Excessive root penetration

Explanation

Too little shielding allows nitrogen and oxygen from the air into the arc, producing porosity in the weld. The correct flow depends on nozzle size, current, and draughts. Excess flow can also cause turbulence and porosity, so the setting must be balanced.

Question 14Welding processes and equipment

In friction stir welding (FSW), how is heat generated to soften the material?

  1. A laser beam focused ahead of the tool
  2. An electric arc between the tool and the workpiece
  3. Friction and plastic deformation between a rotating tool and the workpiece Correct answer.
  4. Combustion of a shielding gas mixture

Explanation

FSW uses a rotating, non-consumable tool whose shoulder and pin generate frictional and deformational heating, softening the material without melting it. The tool then traverses the joint to consolidate it in the solid state. This avoids solidification defects typical of fusion welding.

Question 15Welding processes and equipment

What is the purpose of a copper backing bar in root-pass welding of a butt joint?

  1. To preheat the joint to the required interpass temperature
  2. To provide the shielding gas for the root
  3. To add alloying elements to the root
  4. To support the molten root and control penetration while conducting heat away Correct answer.

Explanation

A copper backing bar supports the molten pool at the root, prevents burn-through, and its high conductivity draws heat away to shape the root bead. It does not add alloy or supply gas. Preheating is a separate operation.

Question 16Welding processes and equipment

Which statement correctly describes the self-regulating arc of a constant-voltage GMAW power source?

  1. Arc length is maintained because a change in arc length changes the burn-off rate to restore equilibrium Correct answer.
  2. Arc length is controlled only by the welder's hand movement
  3. Arc length is independent of wire feed speed
  4. Arc length is fixed by the electrode coating thickness

Explanation

With a constant-voltage characteristic, a shorter arc draws more current, which increases wire burn-off and lengthens the arc back toward equilibrium; a longer arc reduces current and burn-off. This self-regulation keeps the arc length stable. Wire feed speed sets the current.

Question 17Welding processes and equipment

What causes undercut at the edges of a fillet weld during GMAW?

  1. Too small a nozzle diameter
  2. Insufficient shielding gas flow
  3. Excessive travel speed or current melting the base metal without sufficient fill Correct answer.
  4. Using a neutral flame

Explanation

Undercut occurs when the arc melts the base metal at the toe faster than filler is deposited to fill it, typically from excessive current, too fast travel, or poor electrode angle. Reducing current or travel speed and adjusting angle corrects it. Gas flow and nozzle size do not directly create undercut.

Question 18Welding processes and equipment

Which of these is a characteristic advantage of laser beam welding over conventional arc welding?

  1. Ability to weld without any joint preparation at all
  2. Very high energy density giving narrow heat-affected zones and low distortion Correct answer.
  3. Complete freedom from porosity in aluminium alloys
  4. Elimination of the need for shielding gas in all cases

Explanation

Laser welding focuses energy into a small spot, producing a narrow weld and heat-affected zone with low distortion and high speed. Joint fit-up still matters, and shielding gas is often used to protect the hot metal. Porosity can still occur, especially in aluminium.

Question 19Welding processes and equipment

In electroslag welding (ESW), what generates the heat that melts the filler and fuses the joint faces?

  1. A gas flame directed into the joint gap
  2. Electrical resistance of a molten slag bath through which current passes Correct answer.
  3. Mechanical friction between the wire and the plate
  4. An electric arc maintained continuously under the flux

Explanation

ESW uses the resistance heating of a conductive molten slag pool to melt the electrode and joint faces; after initiation, the process runs without an arc. It is a high-productivity process for thick vertical sections. The weld is a casting-like structure with a coarse grain size.

Question 20Welding processes and equipment

Which process uses a continuously fed flux-cored wire with no external shielding gas because the flux provides the shielding?

  1. Plasma arc welding
  2. Self-shielded flux-cored arc welding (FCAW-S) Correct answer.
  3. Gas tungsten arc welding
  4. Submerged arc welding

Explanation

Self-shielded FCAW relies on the flux core to generate shielding gas and slag, so no external gas is supplied. It is useful in windy field conditions. Gas-shielded FCAW, by contrast, uses an external gas supply.

Question 21Welding processes and equipment

Which parameter combination most directly reduces the risk of lack of fusion in multi-pass GMAW of thick steel?

  1. Increased stick-out with a reduced gas flow
  2. A steeper torch angle with no weaving
  3. Lower current and faster travel speed
  4. Adequate current, correct travel speed and interpass cleaning to remove oxides and slag Correct answer.

Explanation

Lack of fusion is prevented by sufficient heat input, appropriate travel speed, and clean joint faces and interpass surfaces. Oxides and slag left between passes inhibit fusion. Reducing current or increasing travel speed lowers heat input and worsens the risk.

Question 22Welding processes and equipment

In resistance spot welding, what determines the size of the weld nugget?

  1. The type of flux coating on the electrode
  2. The welding current, time, and electrode force acting at the interface Correct answer.
  3. The shielding gas composition only
  4. The travel speed of the electrode along the joint

Explanation

Nugget size depends on the heat generated at the sheet interface (I²Rt) and on the electrode force, which controls contact resistance and forging of the nugget. Current and time are the main adjustable parameters. Flux and travel speed are not relevant to spot welding.

Question 23Welding processes and equipment

Which feature of the pulsed GMAW waveform gives controlled, low-average heat input while maintaining spray-type transfer?

  1. An alternating current that reverses polarity each cycle
  2. A constant current below the short-circuit transition
  3. A high background current with a short peak
  4. A peak current pulse above the spray transition followed by a low background current Correct answer.

Explanation

Pulsed GMAW uses a peak current high enough to detach a droplet in spray mode, followed by a low background current that maintains the arc with low average heat input. This allows thinner sections and out-of-position work. A constant low current would give short-circuiting transfer.

Question 24Welding processes and equipment

Which hazard is specific to GTAW and plasma welding and requires the use of adequate local exhaust or respiratory protection when welding stainless steel?

  1. Ozone and nitrogen oxide generation from the intense UV radiation in the arc Correct answer.
  2. Iron oxide dust from the electrode coating
  3. Carbon monoxide from the acetylene cylinder
  4. Lead fume from the copper backing bar

Explanation

The intense ultraviolet radiation of inert-gas arcs produces ozone and nitrogen oxides, which are respiratory irritants. Welding stainless steel also releases hexavalent chromium and nickel fume, so ventilation is essential. These hazards are not linked to the other listed sources.

Question 25Welding processes and equipment

Why is preheating often specified before welding thick, high-carbon or low-alloy steel sections?

  1. To reduce the cooling rate and lower the risk of hydrogen-assisted cold cracking Correct answer.
  2. To increase the oxygen content of the weld pool
  3. To allow the use of a larger electrode without changing current
  4. To eliminate the need for post-weld heat treatment

Explanation

Preheating slows the cooling rate, allowing hydrogen to escape and reducing the formation of hard martensite in the heat-affected zone. This lowers the risk of cold cracking in susceptible steels. It does not replace post-weld heat treatment when that is required.

Question 26Welding processes and equipment

In constant-current (drooping) power sources used for manual metal arc welding, what happens to the welding current when the arc length increases?

  1. The current decreases significantly because the arc voltage rises to match the steeper arc characteristic.
  2. The current increases sharply because the arc voltage falls with increasing length.
  3. The current remains essentially constant because the source has a steeply drooping volt-ampere characteristic. Correct answer.
  4. The current becomes zero immediately because the open-circuit voltage is below the arc voltage.

Explanation

A constant-current (drooping) characteristic means the output current changes very little over the normal arc-voltage range. When the arc lengthens, the arc voltage rises, and the operating point moves along the steep droop, so current stays nearly constant. This self-regulation of current protects against electrode sticking and gives a stable manual arc.

Question 27Welding processes and equipment

Which gas is commonly used as the shielding gas for gas tungsten arc welding (GTAW) of carbon steel when good arc stability and penetration are required?

  1. Argon Correct answer.
  2. Pure helium
  3. Carbon dioxide
  4. Oxygen

Explanation

Argon is the standard shielding gas for GTAW of carbon steel because it provides a stable arc, good cleaning action and adequate penetration at reasonable cost. Helium can be used for higher heat input but is not the common general-purpose choice. Carbon dioxide and oxygen are active gases that would oxidise the tungsten electrode and the weld pool.

Question 28Welding processes and equipment

In gas metal arc welding (GMAW) with a constant-voltage power source, what is the main effect of increasing the wire feed speed while all other settings remain unchanged?

  1. The arc length increases and the current decreases.
  2. The welding current increases and the arc length tends to shorten. Correct answer.
  3. The arc voltage increases proportionally with the wire feed speed.
  4. The welding current decreases and the penetration depth increases.

Explanation

With a constant-voltage characteristic, the power source adjusts current to maintain the set voltage. Increasing wire feed speed pushes more wire into the arc, which temporarily shortens the arc and increases the current until a new equilibrium is reached. The result is a higher burn-off rate and a shorter arc, not a longer one.

Question 29Welding processes and equipment

Which of the following is the primary function of the flux coating on a covered electrode used in manual metal arc welding?

  1. To increase the electrical conductivity of the electrode core wire.
  2. To provide shielding gas and slag, and to stabilise the arc. Correct answer.
  3. To cool the weld pool rapidly and refine the grain structure.
  4. To supply additional filler metal to the joint.

Explanation

The flux coating decomposes in the heat of the arc to generate shielding gas, forms a slag that protects the solidifying weld from oxidation, and contains compounds that stabilise the arc and control its characteristics. It also influences metal transfer and can add alloying elements, but its primary functions are shielding, slag formation and arc stabilisation.

Question 30Welding processes and equipment

A welder is using the keyhole technique in plasma arc welding (PAW) on 8 mm stainless steel. Which combination of parameters is most critical to maintain a stable keyhole and a sound weld?

  1. Maximum plasma gas flow with minimum current and maximum travel speed.
  2. Balanced plasma gas flow, welding current and travel speed, with a suitable orifice and stand-off. Correct answer.
  3. Low welding current with high shielding gas flow and small stand-off distance.
  4. High travel speed with low plasma gas flow and large orifice diameter.

Explanation

Keyhole PAW depends on a precise balance between plasma gas flow, welding current and travel speed. The plasma gas flow and orifice diameter control the force of the constricted arc that penetrates the plate, while current and travel speed control heat input and the stability of the keyhole. Too much gas flow or current can cause the keyhole to collapse or produce cutting, while too little prevents penetration.

Question 31Materials and their behaviour during welding

In the iron-carbon equilibrium diagram, what is the maximum carbon solubility in ferrite (alpha iron) at about 723 °C?

  1. 6.67 %
  2. 0.022 % Correct answer.
  3. 0.8 %
  4. 2.11 %

Explanation

Ferrite is a body-centred cubic solid solution of carbon in alpha iron and can dissolve only a very small amount of carbon; its solubility peaks at roughly 0.022 % at the eutectoid temperature and falls almost to zero at room temperature. The higher figures correspond to other phases or compositions in the diagram.

Question 32Materials and their behaviour during welding

Which transformation product forms when austenite is cooled slowly enough that carbon can diffuse and produce the lamellar structure of alternating ferrite and cementite?

  1. Delta ferrite
  2. Bainite
  3. Pearlite Correct answer.
  4. Martensite

Explanation

Pearlite nucleates and grows by cooperative diffusion of carbon during relatively slow cooling, giving alternating lamellae of ferrite and cementite. Its lamellar spacing depends on the transformation temperature, becoming finer as the temperature falls.

Question 33Materials and their behaviour during welding

A carbon-manganese steel weld metal is described as having an acicular ferrite microstructure. Which property improvement is most directly associated with this microstructure?

  1. Improved toughness through fine interlocking plates Correct answer.
  2. Reduced susceptibility to solidification cracking
  3. Higher resistance to hydrogen-assisted cracking
  4. Increased hardenability of the base plate

Explanation

Acicular ferrite nucleates intragranularly on non-metallic inclusions and produces fine, interlocking plates that deflect cracks, giving a good balance of strength and toughness. It is a microstructural feature of the weld metal rather than a mechanism for hydrogen control or base-plate hardenability.

Question 34Materials and their behaviour during welding

Why does the heat-affected zone of a quenched and tempered steel often show a softened band some distance from the fusion line?

  1. The region undergoes rapid solidification from the melt.
  2. The region is heated above Ac3 and fully re-austenitised.
  3. The region is tempered back to a lower hardness by the welding thermal cycle. Correct answer.
  4. The region absorbs carbon from the weld metal by upgassing.

Explanation

Below the lower critical temperature the original tempered microstructure is over-tempered by the welding heat, so tempering of the pre-existing martensite reduces hardness in a band adjacent to the hardened zone. This softening is a major reason for strength mismatch in welds on quenched and tempered steels.

Question 35Materials and their behaviour during welding

Which alloying element is added to steel primarily to increase hardenability and is controlled carefully in weld metal to avoid excessive hardness?

  1. Phosphorus
  2. Sulphur
  3. Silicon
  4. Manganese Correct answer.

Explanation

Manganese lowers the critical cooling rate and thus raises hardenability, but excessive manganese together with high carbon can produce hard, crack-sensitive microstructures in the heat-affected zone. Sulphur and phosphorus are generally treated as impurities that harm toughness and promote cracking.

Question 36Materials and their behaviour during welding

In the Schaeffler diagram, which quantity is plotted on the vertical axis?

  1. Ferrite number
  2. Chromium equivalent
  3. Nickel equivalent Correct answer.
  4. Carbon equivalent

Explanation

The Schaeffler diagram plots chromium equivalent on the horizontal axis against nickel equivalent on the vertical axis to predict the constitution of stainless steel weld metal. The nickel equivalent combines austenite-stabilising elements such as nickel, carbon and manganese.

Question 37Materials and their behaviour during welding

A 12 % chromium martensitic stainless steel is welded with a matching filler and cools rapidly. What is the principal cracking risk and the usual preventive measure?

  1. Sigma phase embrittlement, prevented by solution annealing after welding
  2. Solidification cracking, prevented by increasing sulphur
  3. Hot cracking, prevented by adding phosphorus
  4. Hydrogen-assisted cold cracking, prevented by preheat and controlled hydrogen Correct answer.

Explanation

Martensitic stainless steels transform to hard martensite on cooling and are sensitive to hydrogen-assisted cold cracking, so preheat, interpass temperature control and low-hydrogen consumables are required. Post-weld heat treatment is often applied after the material has cooled below the martensite finish temperature.

Question 38Materials and their behaviour during welding

Which of the following best explains why aluminium and its alloys require a dedicated welding procedure with careful oxide removal?

  1. Aluminium has a body-centred cubic crystal structure at room temperature.
  2. Aluminium forms a tenacious refractory oxide with a very high melting point. Correct answer.
  3. Aluminium has a very low thermal conductivity.
  4. Aluminium has a high density compared with steel.

Explanation

Aluminium rapidly forms an adherent aluminium oxide film whose melting point is far above that of the metal, so it must be removed mechanically or by cathodic cleaning to allow fusion. The oxide also traps moisture and inclusions that degrade weld quality.

Question 39Materials and their behaviour during welding

Which characteristic of the copper-zinc system makes brasses prone to porosity and zinc fume during fusion welding?

  1. Copper has a very low melting point.
  2. Brass contains more than 2 % carbon.
  3. Zinc has a low boiling point and vaporises readily in the arc. Correct answer.
  4. Zinc forms a protective passive film that excludes shielding gas.

Explanation

Zinc boils at a temperature close to the melting range of many brasses, so it vaporises in the arc, causing fume, porosity and loss of alloying element. This is why welding procedures for brass use low heat input, appropriate fillers and good ventilation.

Question 40Materials and their behaviour during welding

What is the primary reason that nickel alloys are welded with low heat input and controlled interpass temperature?

  1. They have very low thermal expansion.
  2. They cannot be melted by an electric arc.
  3. They are sensitive to hot cracking and to precipitation of embrittling phases. Correct answer.
  4. They contain no alloying elements.

Explanation

Nickel alloys have high hot-cracking susceptibility linked to segregation and low-melting phases, and prolonged exposure at high temperature can precipitate phases that reduce ductility and corrosion resistance. Restricting heat input and interpass temperature limits both effects.

Question 41Materials and their behaviour during welding

Which titanium feature requires that welding be carried out with very effective shielding of the hot metal, including the trailing side and the root?

  1. Titanium has a low melting point.
  2. Titanium contains large amounts of carbon.
  3. Titanium absorbs oxygen, nitrogen and hydrogen at high temperature, causing embrittlement. Correct answer.
  4. Titanium has a face-centred cubic lattice.

Explanation

Above roughly 400–600 °C, titanium reacts readily with oxygen, nitrogen and hydrogen, forming hard, brittle phases and discoloured welds. Shielding must extend beyond the arc to cover the trailing weld and the root side until the metal has cooled below the contamination threshold.

Question 42Materials and their behaviour during welding

A steel has a carbon equivalent (CE) of 0.48 according to the IIW formula. What does this value most directly indicate?

  1. The steel cannot be welded by any arc process.
  2. The steel has an increased risk of cold cracking and needs preheat or controlled hydrogen. Correct answer.
  3. The steel has excellent weldability without any precaution.
  4. The steel must be welded with austenitic stainless filler.

Explanation

The carbon equivalent combines carbon and other alloying elements into a single index of hardenability, and higher values indicate a greater tendency to form hard martensite and crack in the presence of hydrogen and restraint. A CE of 0.48 typically calls for preheat and low-hydrogen practice.

Question 43Materials and their behaviour during welding

Which mechanism is responsible for reheat cracking in the coarse-grained heat-affected zone of low-alloy steels during post-weld heat treatment?

  1. Rapid solidification of the weld metal during the heat treatment
  2. Diffusion of hydrogen out of the weld during heating
  3. Absorption of nitrogen from the furnace atmosphere
  4. Relaxation of residual stress by creep that exceeds the local ductility of the embrittled grain interiors Correct answer.

Explanation

The coarse-grained region is embrittled by precipitation and by impurity segregation to prior austenite grain boundaries, so when residual stresses relax by creep during post-weld heat treatment, the grain interiors cannot accommodate the strain and intergranular cracking occurs. It is a stress-relaxation phenomenon rather than a hydrogen effect.

Question 44Materials and their behaviour during welding

Which statement correctly describes the difference between hot cracking and cold cracking in welded joints?

  1. Hot cracking is caused by hydrogen, while cold cracking is caused by sulphur.
  2. Both occur only in austenitic stainless steels.
  3. Hot cracking occurs only after post-weld heat treatment, while cold cracking occurs in the arc.
  4. Hot cracking occurs at high temperature during solidification, while cold cracking occurs after cooling and is associated with hydrogen and hard microstructure. Correct answer.

Explanation

Hot cracking, also called solidification or liquation cracking, forms at elevated temperature when low-melting films cannot accommodate shrinkage strain. Cold cracking develops below about 200 °C and requires hydrogen, a susceptible microstructure and tensile stress.

Question 45Materials and their behaviour during welding

A fully austenitic stainless steel weld metal (for example type 310) is more prone to solidification cracking than a duplex weld metal. What is the standard explanation?

  1. Austenitic weld metal contains more sulphur than duplex weld metal.
  2. Duplex weld metal has a much higher carbon content.
  3. The absence of ferrite means low-melting segregates form continuous films along solidification boundaries. Correct answer.
  4. Austenitic weld metal solidifies at a lower temperature than duplex weld metal.

Explanation

A small amount of delta ferrite in the weld metal disrupts continuous grain-boundary films and dissolves some sulphur and phosphorus, reducing hot cracking susceptibility. Fully austenitic solidification leaves continuous low-melting films that cannot accommodate shrinkage strain.

Question 46Materials and their behaviour during welding

Which term describes the formation of a hard, brittle layer in the weld metal or heat-affected zone when nitrogen from the atmosphere is absorbed by the molten steel?

  1. Nitride embrittlement Correct answer.
  2. Decarburisation
  3. Spheroidisation
  4. Graphitisation

Explanation

Nitrogen absorbed by molten steel forms brittle nitrides, particularly in steels containing aluminium or titanium, and can also cause porosity and age hardening. Adequate gas shielding and correct consumable handling are the usual controls.

Question 47Materials and their behaviour during welding

Why is the heat-affected zone of a duplex stainless steel at risk of losing corrosion resistance and toughness after welding?

  1. Imbalanced ferrite-austenite ratio and precipitation of nitrides or sigma phase can occur in the zone. Correct answer.
  2. The zone absorbs carbon from the shielding gas.
  3. The zone melts and resolidifies with a coarse grain structure.
  4. The zone becomes fully ferritic and the austenite cannot reform on cooling.

Explanation

Duplex stainless steels rely on a roughly balanced ferrite-austenite structure, and the welding thermal cycle can shift that balance, precipitate chromium nitrides or sigma phase and reduce both toughness and corrosion resistance. Heat input and cooling rate are therefore controlled within a qualified range.

Question 48Materials and their behaviour during welding

Which of the following is the main reason that the weld metal of a high-strength low-alloy steel often has a lower carbon content than the base metal?

  1. To make the weld metal magnetic
  2. To prevent the formation of ferrite
  3. To reduce the risk of solidification cracking and improve toughness Correct answer.
  4. To increase the melting point of the weld metal

Explanation

Matching fillers are usually formulated with lower carbon than the base metal to limit hardenability and cracking while maintaining strength through other alloying elements. Lower carbon also improves weld metal toughness.

Question 49Materials and their behaviour during welding

Which statement about the effect of cooling rate on the hardness of a heat-affected zone in a hardenable steel is correct?

  1. Faster cooling gives higher hardness because more martensite forms. Correct answer.
  2. Faster cooling gives higher hardness only in austenitic stainless steel.
  3. Faster cooling gives lower hardness because less martensite forms.
  4. Cooling rate has no effect on hardness in the heat-affected zone.

Explanation

Rapid cooling suppresses diffusion-controlled transformation, so more austenite transforms to martensite and the hardness rises. This is why thick sections and low heat input increase the cold cracking risk in hardenable steels.

Question 50Materials and their behaviour during welding

Which of the following best describes the effect of sulphur in steel weld metal?

  1. It forms low-melting sulphide films that promote solidification cracking. Correct answer.
  2. It acts as a strong deoxidiser.
  3. It improves toughness by refining the grain structure.
  4. It increases hardenability strongly.

Explanation

Sulphur segregates to solidification boundaries and forms low-melting sulphide films, widening the solidification temperature range and increasing hot cracking susceptibility. It also reduces toughness through inclusion formation, so its content is kept low.