Welding Metallurgy & Materials Flashcards
7 cards from real Architecting on AWS Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Welding Metallurgy & Materials flashcards as text
Which shielding gas mixture is preferred for GMAW of austenitic stainless steel to minimize carbon pickup and carbide precipitation?
Answer: Ar + 5% O2 or Ar + 2% CO2
Argon with a small addition of O2 or CO2 stabilizes the arc and improves wetting without introducing significant carbon that could cause sensitization in the weld metal.
What is the primary metallurgical reason for preheating high-carbon or alloy steels before welding?
Answer: To slow the cooling rate of the HAZ, reducing martensite formation and hydrogen diffusion
Preheat slows HAZ cooling, reducing martensite formation and keeping the steel above the temperature at which hydrogen diffusion stalls, allowing hydrogen to escape before cracking can initiate.
What type of weld discontinuity is described as a planar defect running parallel to the fusion line, caused by poor inter-run fusion during multi-pass welding?
Answer: Lack of inter-run fusion (cold lap)
Cold lap (lack of inter-run fusion) occurs when the previous weld bead is not fully remelted, creating a planar, unbonded interface that acts as a severe stress concentrator.
The toughness of ferritic stainless steel welds is generally poor because of which microstructural characteristic?
Answer: Coarse ferritic grain structure that cannot be refined by heat treatment since there is no allotropic transformation
Ferritic stainless steels do not undergo the austenite-to-ferrite transformation on cooling, so grain growth in the HAZ and weld metal is irreversible and leads to inherently poor toughness.
What is the Ferrite Number (FN) used to measure in weld metal, and which instrument is used to measure it?
Answer: Delta ferrite content, measured by a calibrated magnetic instrument (ferritscope)
The Ferrite Number quantifies delta ferrite in austenitic and duplex stainless steel weld metal; a ferritscope measures the magnetic response of the ferrite phase to determine FN.
In welding aluminum alloys, what is the main cause of porosity in the weld metal?
Answer: Hydrogen dissolved in the molten pool that becomes insoluble upon solidification
Hydrogen is highly soluble in molten aluminum but nearly insoluble in solid aluminum; upon solidification, the excess hydrogen forms pores that are trapped in the weld metal.
What is the purpose of using an E309 filler metal when welding carbon steel to austenitic stainless steel (dissimilar metal weld)?
Answer: E309's higher Cr and Ni content dilutes the carbon steel contribution while maintaining an austenitic weld metal
E309 contains more Cr and Ni than E308 so that even after significant dilution from the carbon steel base metal, the final weld deposit remains austenitic without martensite formation.