Heat Input and Distortion Control Flashcards
7 cards from real Certified Welder practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Heat Input and Distortion Control flashcards as text
The heat affected zone (HAZ) in a weldment is best described as:
Answer: Base metal that was not melted but had its microstructure altered by welding heat
The HAZ is the portion of the base metal that was never melted but experienced temperatures high enough to alter its microstructure and mechanical properties.
In the HAZ region immediately adjacent to the fusion line, what typically happens to grain structure?
Answer: Grain coarsening occurs due to exposure to very high temperatures
The coarse-grain HAZ region closest to the fusion line reaches near-melting temperatures, promoting significant grain growth that can reduce impact toughness.
Residual stresses in weldments are primarily caused by:
Answer: Differential thermal expansion and contraction during welding and cooling
Residual stresses are locked in because different regions of the weld and HAZ heat and cool at different rates, causing non-uniform plastic deformation that remains after cooling.
What is the primary purpose of post-weld heat treatment (PWHT)?
Answer: To relieve residual stresses and improve toughness in the HAZ
PWHT reduces residual stresses and HAZ hardness while improving toughness, making it essential for pressure vessels, high-strength steels, and code-required applications.
Cold cracking (hydrogen-induced cracking) in steel weldments is characterized by:
Answer: Potentially occurring hours or days after welding as hydrogen migrates to stress points
Hydrogen-induced cracking is delayed because it requires time for diffusible hydrogen to migrate to stress concentration areas; cracking may not appear until hours or days after welding.
As carbon content and alloying elements increase in steel, the required preheat temperature generally:
Answer: Increases because the carbon equivalent rises, increasing hardenability and cracking risk
Higher carbon equivalent increases hardenability, meaning the steel cools to form hard martensite more easily; higher preheat slows cooling to reduce cracking risk.
What is the primary risk of allowing interpass temperature to rise excessively above the specified maximum?
Answer: Degraded mechanical properties due to grain growth and over-tempering
Excessive interpass temperature keeps the weld region at elevated temperatures too long, promoting grain growth and over-tempering that reduces yield strength and toughness.