Question:
Which one of the following fusion welding techniques results in least Heat-Affected Zone (HAZ)?
Which one of the following fusion welding techniques results in least Heat-Affected Zone (HAZ)?
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A narrower HAZ comes from a more concentrated, faster heat source with lower total heat input; compare the energy density of SAW, TIG, EBW, and OAW.
Updated On: Jul 28, 2026
- Submerged Arc Welding (SAW)
- Tungsten Inert Gas Welding (TIG)
- Electron Beam Welding (EBW)
- Oxy-Acetylene Welding (OAW)
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Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Understand what the Heat-Affected Zone means.
The Heat-Affected Zone (HAZ) is the region of base metal next to the weld that does not melt, but gets hot enough during welding for its microstructure and properties to change. A wide HAZ means more of the surrounding metal loses strength or gets brittle, so a narrow HAZ is desired.
Step 2: Identify what controls the width of the HAZ.
The HAZ width depends mainly on the heat input per unit length of weld, and on how fast that heat is delivered and how well it is focused. A process that puts a large amount of energy into a very small, tightly focused spot for a very short time heats the base metal quickly but does not give the surrounding material time to absorb much heat by conduction, so the HAZ stays narrow. A process that spreads heat over a wider area, or uses a slower and less concentrated heat source, lets more heat conduct sideways into the base metal, so the HAZ becomes wider.
Step 3: Rank the four processes by energy density.
(A) Submerged Arc Welding (SAW): Uses a continuous arc under a blanket of granular flux with high current, giving high heat input and a relatively wide HAZ.
(B) Tungsten Inert Gas Welding (TIG): Uses a focused arc under inert gas shielding, more concentrated than SAW, but the arc still spreads over a broader area than a beam process, giving a moderate HAZ.
(C) Electron Beam Welding (EBW): Uses a high velocity beam of electrons focused electromagnetically to an extremely small spot, giving the highest energy density of the four processes, very fast welding speed, and very low total heat input. This produces the narrowest HAZ.
(D) Oxy-Acetylene Welding (OAW): Uses a gas flame, which is the least concentrated heat source among the four, has a slow welding speed, and delivers heat over a wide area, giving the widest HAZ.
Step 4: Final conclusion.
Among SAW, TIG, EBW, and OAW, Electron Beam Welding has the most concentrated and fastest heat source, so it results in the
\[ \boxed{\text{least Heat-Affected Zone (Electron Beam Welding)}} \]
Hence, the correct option is (C).
The Heat-Affected Zone (HAZ) is the region of base metal next to the weld that does not melt, but gets hot enough during welding for its microstructure and properties to change. A wide HAZ means more of the surrounding metal loses strength or gets brittle, so a narrow HAZ is desired.
Step 2: Identify what controls the width of the HAZ.
The HAZ width depends mainly on the heat input per unit length of weld, and on how fast that heat is delivered and how well it is focused. A process that puts a large amount of energy into a very small, tightly focused spot for a very short time heats the base metal quickly but does not give the surrounding material time to absorb much heat by conduction, so the HAZ stays narrow. A process that spreads heat over a wider area, or uses a slower and less concentrated heat source, lets more heat conduct sideways into the base metal, so the HAZ becomes wider.
Step 3: Rank the four processes by energy density.
(A) Submerged Arc Welding (SAW): Uses a continuous arc under a blanket of granular flux with high current, giving high heat input and a relatively wide HAZ.
(B) Tungsten Inert Gas Welding (TIG): Uses a focused arc under inert gas shielding, more concentrated than SAW, but the arc still spreads over a broader area than a beam process, giving a moderate HAZ.
(C) Electron Beam Welding (EBW): Uses a high velocity beam of electrons focused electromagnetically to an extremely small spot, giving the highest energy density of the four processes, very fast welding speed, and very low total heat input. This produces the narrowest HAZ.
(D) Oxy-Acetylene Welding (OAW): Uses a gas flame, which is the least concentrated heat source among the four, has a slow welding speed, and delivers heat over a wide area, giving the widest HAZ.
Step 4: Final conclusion.
Among SAW, TIG, EBW, and OAW, Electron Beam Welding has the most concentrated and fastest heat source, so it results in the
\[ \boxed{\text{least Heat-Affected Zone (Electron Beam Welding)}} \]
Hence, the correct option is (C).
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