AWS AWS Weld Metallurgy & Heat Treatment 1 — Questions and Answers
Question 1: The heat-affected zone (HAZ) in welding is defined as:
- The area where filler metal has been deposited
- The base metal area that has been melted during welding
- The base metal area altered by welding heat without melting (Correct answer)
- The zone where weld spatter has been deposited
Correct answer: The base metal area altered by welding heat without melting
The HAZ is the portion of the base metal that was not melted but whose microstructure and mechanical properties were altered by the heat of welding.
Question 2: Martensite in steel welds is:
- A soft, ductile phase that improves weld toughness
- A hard, brittle phase formed by rapid cooling of austenite (Correct answer)
- A phase that forms during slow controlled cooling
- A protective oxide layer on the weld surface
Correct answer: A hard, brittle phase formed by rapid cooling of austenite
Martensite is a hard, brittle microstructure that forms when austenite is cooled too rapidly, and can lead to cracking in the HAZ.
Question 3: Carbon equivalent (CE) is used to predict:
- The carbon content of the filler metal
- The susceptibility of steel to hydrogen-induced cracking (Correct answer)
- The melting point of the base metal
- The tensile strength of the completed weld
Correct answer: The susceptibility of steel to hydrogen-induced cracking
Carbon equivalent is a formula combining carbon and other alloying elements to predict hardenability and susceptibility to hydrogen-induced cracking.
Question 4: Hydrogen-induced cracking (HIC) in welds is most likely to occur:
- During welding at elevated temperatures
- Immediately after solidification of the weld pool
- After the weld has cooled below 150°C (300°F) (Correct answer)
- Only in non-ferrous metals
Correct answer: After the weld has cooled below 150°C (300°F)
Hydrogen-induced cracking (cold cracking) typically occurs after the weld cools below 150°C because hydrogen diffuses to stress concentration areas as the metal becomes more brittle.
Question 5: Austenite in steel exists:
- At room temperature in all steels
- At elevated temperatures in a face-centered cubic structure (Correct answer)
- Only in stainless steels at all temperatures
- Below the martensite start temperature
Correct answer: At elevated temperatures in a face-centered cubic structure
Austenite is the high-temperature face-centered cubic (FCC) phase of steel that exists above the critical transformation temperature.
Question 6: Solidification cracking in welds is primarily caused by:
- Excessive preheat temperature
- Low-temperature hydrogen embrittlement
- Low-melting-point impurities segregating to grain boundaries during solidification (Correct answer)
- Excessive post-weld heat treatment
Correct answer: Low-melting-point impurities segregating to grain boundaries during solidification
Solidification (hot) cracking occurs when low-melting-point impurities like sulfur and phosphorus segregate to grain boundaries and remain liquid as the surrounding metal solidifies and contracts.
AWS AWS Weld Metallurgy & Heat Treatment 1
The heat-affected zone (HAZ) in welding is defined as: