WCL Metallurgy & Material Science 4

Question 1

What is 'stress corrosion cracking' (SCC) and which condition promotes it?

Accepted Answer

Cracking resulting from simultaneous tensile stress and a corrosive environment

Answer

SCC requires the simultaneous presence of a susceptible material, tensile stress (residual or applied), and a specific corrosive environment to propagate.

Question 2

Why does welding austenitic stainless steel with high heat input increase risk of sensitization?

Accepted Answer

High heat input keeps the metal in the sensitization temperature range longer

Answer

Greater heat input extends time in the 800°F–1500°F sensitization range, giving more opportunity for chromium carbides to precipitate at grain boundaries.

Question 3

What is the primary advantage of using low-hydrogen (EXX18) electrodes when welding high-strength steel?

Accepted Answer

They minimize diffusible hydrogen in the weld, reducing cold cracking risk

Answer

Low-hydrogen electrodes have moisture-resistant coatings that limit diffusible hydrogen pickup in the weld metal, directly reducing hydrogen-induced cold cracking susceptibility.

Question 4

Which crystal structure do most common austenitic stainless steels (e.g., 304, 316) exhibit at room temperature?

Accepted Answer

Face-centered cubic (FCC)

Answer

Nickel stabilizes the austenite phase, which has an FCC crystal structure, in these stainless steels even at room temperature.

Question 5

What metallurgical problem can arise when welding aluminum alloys in the 6xxx series (e.g., 6061)?

Accepted Answer

Loss of precipitation hardening strength in the HAZ

Answer

Heat from welding dissolves the Mg2Si precipitates that provide 6xxx-series strength, overaging or annealing the HAZ and significantly reducing its mechanical properties.

(WCL) Welding Certification Los Angeles Practice Test

(WCL) Welding Certification Los Angeles Practice Test

WCL Metallurgy & Material Science 4