CWS CWS Metallurgy & Material Properties 2 — Questions and Answers
Question 1: Which type of stainless steel is generally considered non-magnetic and cannot be hardened by heat treatment?
- Martensitic stainless steel
- Ferritic stainless steel
- Austenitic stainless steel (Correct answer)
- Duplex stainless steel
Correct answer: Austenitic stainless steel
Austenitic stainless steels (300 series) have a face-centered cubic (FCC) structure that makes them non-magnetic and not hardenable by heat treatment.
Question 2: What welding phenomenon is characterized by intergranular cracking in the HAZ of nickel-base alloys during welding?
- Hot cracking
- Liquation cracking (Correct answer)
- Lamellar tearing
- Stress corrosion cracking
Correct answer: Liquation cracking
Liquation cracking occurs in the partially-melted zone (PMZ) of the HAZ when low-melting-point constituents at grain boundaries liquefy during welding.
Question 3: A CWS supervisor is working with ASTM A36 and A514 steel in the same structure. What is the correct filler metal selection for a critical joint between these two steels?
- Match the stronger A514 steel
- Match the weaker A36 steel (Correct answer)
- Use an austenitic stainless filler
- Use the average strength between both steels
Correct answer: Match the weaker A36 steel
When joining dissimilar strength steels, the filler metal should match the lower-strength base metal (A36) to maintain joint ductility and avoid cracking.
Question 4: What is 'lamellar tearing' and in what base metal orientation does it most commonly occur?
- Surface cracking from excessive heat input; occurs longitudinally
- Subsurface cracking from through-thickness stress on plate with low short-transverse ductility; occurs in the Z-direction (Correct answer)
- Centerline cracking from solidification; occurs in the weld metal
- Cold cracking from hydrogen; occurs in the HAZ parallel to fusion line
Correct answer: Subsurface cracking from through-thickness stress on plate with low short-transverse ductility; occurs in the Z-direction
Lamellar tearing is subsurface cracking caused by through-thickness (Z-direction) tensile stress in rolled plate with non-metallic inclusions aligned parallel to the surface.
Question 5: What does a high carbon equivalent (CE > 0.45) indicate about a steel's weldability?
- Excellent weldability with no precautions needed
- Increased susceptibility to hydrogen-induced cold cracking, requiring preheat (Correct answer)
- Better resistance to hot cracking
- Higher resistance to sensitization
Correct answer: Increased susceptibility to hydrogen-induced cold cracking, requiring preheat
A carbon equivalent above 0.45 indicates the steel will harden significantly in the HAZ, making it susceptible to hydrogen-induced cold cracking and requiring preheat.
Question 6: Which welding process is most commonly associated with hydrogen-induced cracking due to inherent hydrogen sources in the consumables?
- GMAW with solid wire
- GTAW with bare wire
- SMAW with low-hydrogen electrodes
- SMAW with cellulosic (EXX10) electrodes (Correct answer)
Correct answer: SMAW with cellulosic (EXX10) electrodes
Cellulosic SMAW electrodes (EXX10) have high cellulose content that produces significant hydrogen, making HICC a major concern when used on hardenable steels.
CWS CWS Metallurgy & Material Properties 2
Which type of stainless steel is generally considered non-magnetic and cannot be hardened by heat treatment?