Architecting on AWS Certification Welding Metallurgy & Materials 5

Question 1

What is the 'nil ductility transition temperature' (NDT) and why is it important in welded structural design?

Accepted Answer

The temperature below which fracture mode transitions from ductile to brittle, determining the minimum safe operating temperature for welded structures

Answer

The NDT is the temperature below which a material fractures without plastic deformation; structural components must not operate below this temperature to avoid catastrophic brittle fracture.

Question 2

Which alloying element in nickel-base superalloy filler metals is primarily responsible for their high-temperature strength and oxidation resistance?

Accepted Answer

Chromium

Answer

Chromium forms a protective Cr2O3 oxide scale that provides oxidation resistance and also solid-solution strengthens the nickel matrix at elevated temperatures.

Question 3

What is 'solidification cracking' and during which phase of the welding thermal cycle does it occur?

Accepted Answer

A crack that forms in the weld metal during the final stages of solidification when liquid films are present between dendrites

Answer

Solidification cracking (hot cracking) occurs when low-melting liquid films persist between dendrites near the solidus temperature and cannot withstand the tensile stresses from thermal contraction.

Question 4

In FCAW and SMAW, what is the primary function of the slag that forms on top of the weld bead?

Accepted Answer

To protect the hot weld metal from atmospheric contamination and control cooling rate

Answer

Slag shields the solidifying weld metal from oxygen and nitrogen, and its thermal insulation slows cooling, reducing susceptibility to martensite formation and improving mechanical properties.

Question 5

What is 'stress corrosion cracking' (SCC) in welded structures, and which combination of conditions is required for it to occur?

Accepted Answer

Simultaneous presence of a susceptible material, a corrosive environment, and tensile stress (residual or applied)

Answer

SCC requires the simultaneous combination of a susceptible material, a specific corrosive medium, and sufficient tensile stress; removing any one factor prevents cracking.

Architecting on AWS Certification Practice Test

Architecting on AWS Certification Practice Test

Architecting on AWS Certification Welding Metallurgy & Materials 5