AWS AWS Metallurgy & Materials 2 — Questions and Answers
Question 1: What is the purpose of Post-Weld Heat Treatment (PWHT)?
- To increase porosity in the weld
- To harden the weld deposit
- To relieve residual stresses and temper hard microstructures (Correct answer)
- To add carbon to the weld metal
Correct answer: To relieve residual stresses and temper hard microstructures
PWHT reduces residual stresses, improves toughness, and tempers hardened zones in the weld and HAZ.
Question 2: Which test is commonly used to evaluate the toughness (notch impact energy) of a weld metal at low temperatures?
- Brinell hardness test
- Charpy V-notch impact test (Correct answer)
- Vickers microhardness test
- Rockwell C test
Correct answer: Charpy V-notch impact test
The Charpy V-notch impact test measures absorbed energy to assess toughness, especially at low temperatures.
Question 3: In welding metallurgy, what is 'sensitization' associated with in austenitic stainless steel?
- Formation of ferrite stringers
- Chromium carbide precipitation at grain boundaries, depleting chromium from the grain boundary region (Correct answer)
- Excessive grain growth in the HAZ
- Formation of sigma phase at high temperatures
Correct answer: Chromium carbide precipitation at grain boundaries, depleting chromium from the grain boundary region
Sensitization occurs when chromium carbides precipitate at grain boundaries, creating chromium-depleted zones susceptible to intergranular corrosion.
Question 4: What does the carbon equivalent (CE) formula help predict?
- The weld travel speed needed
- The susceptibility of steel to hydrogen-induced cracking (Correct answer)
- The amount of filler metal needed
- The voltage required for GMAW
Correct answer: The susceptibility of steel to hydrogen-induced cracking
The carbon equivalent (CE) formula estimates a steel's hardenability and its susceptibility to hydrogen-induced cracking.
Question 5: Which microstructure in the HAZ of steel welds is most susceptible to hydrogen-assisted cracking?
- Pearlite
- Ferrite
- Martensite (Correct answer)
- Austenite
Correct answer: Martensite
Martensite's high hardness and brittleness make it the microstructure most susceptible to hydrogen-assisted cracking.
Question 6: Aluminum alloys are generally more difficult to weld than mild steel primarily because of:
- Their very high melting point
- The stable oxide layer (Al₂O₃) that reforms instantly (Correct answer)
- Their tendency to form martensite
- High carbon content
Correct answer: The stable oxide layer (Al₂O₃) that reforms instantly
Aluminum's tenacious oxide layer (Al₂O₃) has a much higher melting point than the base metal and must be removed during welding.
AWS AWS Metallurgy & Materials 2
What is the purpose of Post-Weld Heat Treatment (PWHT)?