AWS AWS Metallurgy & Materials 5

Question 1

What microstructural feature is responsible for the high hardness of martensite in steel?

Accepted Answer

Supersaturated solid solution of carbon in a BCT iron lattice

Answer

Martensite's extreme hardness results from carbon atoms being trapped in a distorted body-centered tetragonal lattice, creating high internal strain.

Question 2

In a copper-zinc (brass) alloy weld, which problem is most likely to occur due to the low boiling point of zinc?

Accepted Answer

Porosity from zinc vaporization

Answer

Zinc has a boiling point below typical welding temperatures, causing it to vaporize and create porosity and toxic fume hazards.

Question 3

What does a high carbon equivalent (CE) value indicate about a steel's weldability?

Accepted Answer

Poor weldability with increased risk of hydrogen cracking and HAZ hardening

Answer

A high CE indicates the steel will harden significantly in the HAZ and is susceptible to hydrogen-induced cracking, requiring preheat and low-hydrogen procedures.

Question 4

Which phenomenon occurs when two dissimilar metals with different electrochemical potentials are joined by welding and exposed to an electrolyte?

Accepted Answer

Galvanic corrosion

Answer

Galvanic corrosion occurs when dissimilar metals in electrical contact are exposed to an electrolyte, causing the more active (anodic) metal to corrode preferentially.

Question 5

What is the function of titanium or niobium additions in stabilized austenitic stainless steels used for welding?

Accepted Answer

To preferentially combine with carbon and prevent chromium carbide sensitization

Answer

Ti and Nb have stronger affinity for carbon than chromium does, forming their own carbides and preventing the chromium depletion that causes sensitization.

AWS Practice Test

AWS Practice Test

AWS AWS Metallurgy & Materials 5