Architecting on AWS Certification Welding Metallurgy & Materials 2

Question 1

What is the primary cause of hydrogen-induced cracking (HIC) in high-strength steel welds?

Accepted Answer

Diffusible hydrogen trapped in the heat-affected zone under residual stress

Answer

Hydrogen-induced cracking occurs when diffusible hydrogen migrates to the HAZ and combines with residual tensile stress and a susceptible microstructure.

Question 2

Which welding process is most commonly used for joining austenitic stainless steel to minimize sensitization?

Accepted Answer

Gas Tungsten Arc Welding (GTAW) with low heat input

Answer

GTAW with low heat input minimizes the time spent in the sensitization temperature range (450–850°C), reducing chromium carbide precipitation at grain boundaries.

Question 3

The Schaeffler diagram is used to predict the weld metal microstructure of stainless steels based on which two parameters?

Accepted Answer

Chromium equivalent and nickel equivalent

Answer

The Schaeffler diagram maps weld metal microstructure (austenite, ferrite, martensite) as a function of chromium equivalent (ferrite stabilizers) versus nickel equivalent (austenite stabilizers).

Question 4

What microstructural feature in low-alloy steel HAZ is most detrimental to toughness?

Accepted Answer

Upper bainite

Answer

Upper bainite contains coarse carbide films along lath boundaries that act as cleavage crack initiators, severely reducing Charpy impact toughness.

Question 5

Which phenomenon describes the loss of corrosion resistance in austenitic stainless steel due to chromium depletion near grain boundaries?

Accepted Answer

Sensitization

Answer

Sensitization occurs when chromium carbides precipitate at grain boundaries during heating to 450–850°C, depleting the adjacent matrix of chromium below the passive threshold (~12%).

Architecting on AWS Certification Practice Test

Architecting on AWS Certification Practice Test

Architecting on AWS Certification Welding Metallurgy & Materials 2