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CWI Heat Control and Metallurgy practice questions

Carbon and low-alloy steel metallurgy: heat-affected zone, hydrogen cracking, preheat and interpass temperature, heat treatment and mechanical properties. This domain is about 7% of the exam. Try each question, then open the answer.

Read the Heat Control and Metallurgy study guide

Question 1

All else being equal, which joint normally needs the higher preheat?
  1. A joint in 1/4 in. thick plate
  2. A joint in 1/8 in. thick sheet
  3. A joint in 2 in. thick plate
  4. Thickness has no effect on preheat
Show answer

Answer: C. A joint in 2 in. thick plate

Thicker material is a bigger heat sink, so welds cool faster and form harder structures. Codes such as AWS D1.1 raise minimum preheat as thickness increases.

Source: AWS Welding Handbook, 9th ed., Vol. 1 (Welding Science and Technology) (cooling rate); AWS D1.1:2020 Clause 5 (prequalified preheat table)

Question 2

A higher carbon equivalent (CE) for a steel generally means:
  1. Lower hardenability and less need for preheat
  2. Better corrosion resistance
  3. Greater hardenability and a greater need for preheat
  4. Lower tensile strength
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Answer: C. Greater hardenability and a greater need for preheat

Carbon equivalent combines carbon with weighted amounts of other alloying elements to estimate hardenability. As CE rises, the HAZ more easily forms martensite, so more preheat and hydrogen control are needed.

Source: AWS Welding Handbook, 9th ed., Vol. 1 (Welding Science and Technology) (carbon equivalent); AWS D1.1:2020, informative annex on alternative methods for determining preheat (Annex H in D1.1:2015; annex lettering may differ by edition)

Question 3

Which heat treatment heats steel above the upper critical temperature and cools it in still air to refine the grain structure?
  1. Normalizing
  2. Full annealing
  3. Stress relieving
  4. Quenching
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Answer: A. Normalizing

Normalizing heats steel into the austenite range and cools it in air. This gives a finer, more uniform grain structure than the as-rolled or as-welded condition.

Source: AWS Welding Handbook, 9th ed., Vol. 1 (Welding Science and Technology), chapter on physical metallurgy (heat treatment)

Question 4

Which element in steel is most associated with hot (solidification) cracking when present in excess?
  1. Manganese
  2. Nickel
  3. Silicon
  4. Sulfur
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Answer: D. Sulfur

Sulfur forms low-melting iron sulfide films at grain boundaries, which can tear apart as the weld solidifies. Manganese ties sulfur up as manganese sulfide, so a good Mn-to-S ratio reduces hot cracking.

Source: AWS Welding Handbook, 9th ed., Vol. 1 (Welding Science and Technology), chapter on welding metallurgy (hot cracking)

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