Architecting on AWS Certification Welding Metallurgy & Materials 3 — Questions and Answers
Question 1: What is the significance of the carbon equivalent (CE) formula in welding?
- It predicts the ultimate tensile strength of the weld metal
- It estimates hardenability and susceptibility to cold cracking in the HAZ (Correct answer)
- It determines the required shielding gas mixture for GMAW
- It calculates the minimum preheat temperature for stainless steels
Correct answer: It estimates hardenability and susceptibility to cold cracking in the HAZ
The carbon equivalent combines carbon and alloying element content into a single value that predicts HAZ hardenability; higher CE means greater susceptibility to cold cracking and the need for preheat.
Question 2: Which solidification mode in austenitic stainless steel weld metal is most resistant to solidification cracking?
- Fully austenitic (A mode)
- Primary austenitic with secondary ferrite (AF mode)
- Primary ferritic with secondary austenite (FA mode) (Correct answer)
- Fully ferritic (F mode)
Correct answer: Primary ferritic with secondary austenite (FA mode)
FA solidification mode produces delta ferrite that rejects tramp elements (S, P) into the liquid last, preventing low-melting liquid films at grain boundaries that cause solidification cracking.
Question 3: What is the role of manganese in low-alloy steel filler metals?
- Acts as a carbide stabilizer to prevent sensitization
- Deoxidizes the weld pool and combines with sulfur to form MnS, preventing hot cracking (Correct answer)
- Increases the austenite-to-ferrite transformation temperature
- Promotes columnar grain growth in the weld metal
Correct answer: Deoxidizes the weld pool and combines with sulfur to form MnS, preventing hot cracking
Manganese is a deoxidizer in weld pools and preferentially combines with sulfur to form globular MnS inclusions, preventing the formation of low-melting iron sulfide films that cause hot cracking.
Question 4: The heat-affected zone (HAZ) of a steel weld is divided into sub-zones. Which sub-zone experiences the highest peak temperature and coarsest grain structure?
- Subcritical HAZ
- Intercritical HAZ
- Coarse-grained HAZ (CGHAZ) (Correct answer)
- Fine-grained HAZ (FGHAZ)
Correct answer: Coarse-grained HAZ (CGHAZ)
The coarse-grained HAZ, immediately adjacent to the fusion line, reaches temperatures above 1100°C, causing rapid austenite grain growth that can lead to martensite with poor toughness upon cooling.
Question 5: What welding defect is characterized by a groove melted into the base metal adjacent to the weld toe that is not filled by weld metal?
- Porosity
- Incomplete fusion
- Undercut (Correct answer)
- Cold lap
Correct answer: Undercut
Undercut is a groove or channel melted into the base metal at the weld toe caused by excessive amperage, improper electrode angle, or travel speed, creating a stress concentration.
Question 6: In submerged arc welding (SAW), what is the primary function of the flux?
- To provide the arc shielding gas
- To shield the arc and molten pool, deoxidize the weld metal, and add alloying elements (Correct answer)
- To preheat the base metal ahead of the arc
- To control the travel speed of the welding head
Correct answer: To shield the arc and molten pool, deoxidize the weld metal, and add alloying elements
SAW flux shields the arc and weld pool from the atmosphere, deoxidizes and denitrogenizes the weld metal, and can add beneficial alloying elements through metallurgical reactions.
Question 7: What is lamellar tearing, and which base metal orientation makes it most likely to occur?
- A ductile fracture in the through-thickness direction, most likely in plate with high sulfur content under through-thickness tensile stress (Correct answer)
- A brittle fracture along columnar grain boundaries in the weld metal
- A fatigue crack initiating at the weld toe under cyclic loading
- A stress corrosion crack in the HAZ of high-strength alloys
Correct answer: A ductile fracture in the through-thickness direction, most likely in plate with high sulfur content under through-thickness tensile stress
Lamellar tearing is a step-like fracture below the HAZ caused by MnS inclusions aligned in the rolling direction, triggered by through-thickness tensile stress in joints like T-joints and corner joints.
Architecting on AWS Certification Welding Metallurgy & Materials 3
What is the significance of the carbon equivalent (CE) formula in welding?