Architecting on AWS Certification Welding Metallurgy & Materials 4

Question 1

Which shielding gas mixture is preferred for GMAW of austenitic stainless steel to minimize carbon pickup and carbide precipitation?

Accepted Answer

Ar + 5% O2 or Ar + 2% CO2

Answer

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.

Question 2

What is the primary metallurgical reason for preheating high-carbon or alloy steels before welding?

Accepted Answer

To slow the cooling rate of the HAZ, reducing martensite formation and hydrogen diffusion

Answer

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.

Question 3

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?

Accepted Answer

Lack of inter-run fusion (cold lap)

Answer

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.

Question 4

The toughness of ferritic stainless steel welds is generally poor because of which microstructural characteristic?

Accepted Answer

Coarse ferritic grain structure that cannot be refined by heat treatment since there is no allotropic transformation

Answer

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.

Question 5

What is the Ferrite Number (FN) used to measure in weld metal, and which instrument is used to measure it?

Accepted Answer

Delta ferrite content, measured by a calibrated magnetic instrument (ferritscope)

Answer

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.

Architecting on AWS Certification Practice Test

Architecting on AWS Certification Practice Test

Architecting on AWS Certification Welding Metallurgy & Materials 4