WCL Metallurgy & Material Science 5

Question 1

What is the primary metallurgical difference between 'ferrite' and 'austenite' in steel?

Accepted Answer

Ferrite is BCC and magnetic; austenite is FCC and non-magnetic

Answer

Ferrite has a BCC crystal structure, is magnetic, and dissolves very little carbon; austenite is FCC, non-magnetic, and can dissolve significantly more carbon.

Question 2

Which titanium alloy type is considered most weldable?

Accepted Answer

Commercially pure (CP) alpha titanium

Answer

Commercially pure titanium (alpha phase) is the most weldable because it does not undergo the complex phase transformations that can embrittle alpha-beta and beta alloys during welding.

Question 3

When welding dissimilar metals with widely different coefficients of thermal expansion, which weld defect is most likely?

Accepted Answer

Cracking or delamination due to differential thermal stresses

Answer

Mismatched thermal expansion causes differential contraction on cooling, generating residual stresses that can crack the joint or delaminate the bond at the fusion interface.

Question 4

What is 'weld dilution' and why does it matter when selecting filler metal?

Accepted Answer

The mixing of base metal into the weld pool, changing the deposit's composition

Answer

Dilution is the percentage of base metal that melts into the weld pool; high dilution can alter the chemical composition of the deposit away from the filler metal's nominal analysis, affecting corrosion resistance or strength.

Question 5

Which heat treatment process is used to remove brittleness from hardened steel by heating below the lower critical temperature?

Accepted Answer

Tempering

Answer

Tempering heats hardened steel to a sub-critical temperature (typically 300°F–1300°F), relieving internal stresses and reducing brittleness while retaining useful hardness.

(WCL) Welding Certification Los Angeles Practice Test

(WCL) Welding Certification Los Angeles Practice Test

WCL Metallurgy & Material Science 5