AWS Weld Metallurgy & Heat Treatment Flashcards

Which weld zone is defined as the region that reached temperatures above the liquidus but below the solidus during welding?

Answer: Partially melted zone (PMZ)

The partially melted zone (PMZ) experienced temperatures between the solidus and liquidus, resulting in partial melting at grain boundaries.

What type of transformation occurs in plain carbon steel when rapidly cooled from the austenite region?

Answer: Martensitic transformation

Rapid cooling (quenching) of austenite in plain carbon steel produces martensite, a hard and brittle body-centered tetragonal (BCT) structure.

What is the role of interpass temperature control in multi-pass welding of low-alloy steels?

Answer: Maintains heat input within acceptable limits to control microstructure and avoid excessive softening or cracking

Controlling interpass temperature prevents excessive cumulative heat input, which could cause grain coarsening, loss of toughness, or reheat cracking in certain steels.

Sigma phase formation in stainless steel welds is most problematic because it:

Answer: Reduces toughness and corrosion resistance, especially at elevated temperatures

Sigma phase is a hard, brittle intermetallic compound that forms in duplex and ferritic stainless steels, severely reducing impact toughness and corrosion resistance.

In welding carbon steel, what is the purpose of a stress relief heat treatment performed below the lower critical temperature (Ac1)?

Answer: To reduce residual welding stresses without significantly altering the existing microstructure

Stress relief at sub-critical temperatures reduces residual stresses through plastic flow without causing phase transformation, preserving the existing microstructure.

What is the primary cause of lamellar tearing in welded joints?

Answer: Low through-thickness ductility in rolled plate due to planar inclusions, loaded in the Z-direction by weld shrinkage

Lamellar tearing occurs when weld shrinkage strains load rolled steel through its thickness, causing separation along planar sulfide or oxide inclusions with low Z-direction ductility.

How does ferrite content in austenitic stainless steel weld metal help prevent solidification cracking?

Answer: Ferrite dissolves harmful impurities like sulfur and phosphorus, reducing their segregation to grain boundaries

Ferrite in austenitic stainless steel weld metal dissolves and ties up sulfur and phosphorus, preventing the formation of low-melting-point films that cause solidification cracking.