§2.3 · Making the weld
Heat control and metallurgy for the CWI
Welding metallurgy on the CWI follows one chain. How fast the weld and its heat-affected zone cool sets the microstructure. The microstructure sets hardness and toughness. Hardness, plus hydrogen and restraint, decides whether it cracks. The B5.1:2025 name for the area, Base Materials, Heat Treatments and Metallurgy (Ferrous), tells you the scope: steels only.
- Exam
- CWI
- Clause
- §2.3
- Tags here
- 15
- Part A minimum
- at least 6%
2.3.1From heat to cracks
2.3.2Cooling rate runs the show
Three things decide how fast a weld cools: the heat put in, the preheat, and the mass of steel around the joint soaking heat away. Heat input and preheat are the two the welder and the WPS control; the torch side is on welding application and control. Preheat is the one codes lean on, and it's set apart from interpass temperature on preheat vs interpass temperature. Heat input as a number is worked on welding calculations.
Chemistry decides how hard a steel gets at a given cooling rate. Carbon equivalent rolls the chemistry into one number so you can compare steels and set preheat. The higher it is, the more care the joint needs.
Across the heat-affected zone
Peak temperature falls with distance from the fusion line, so one weld leaves a band of different structures in the base metal. Some of the HAZ was heated above the transformation range and some only partly into it. Past that is tempered metal and then unaffected base metal. Hardness surveys and Charpy specimens notched in the HAZ exist because of this band; the tests themselves are on destructive testing.
Base metal and filler on paper
B5.1:2025 makes verifying base material and filler metal compliance, and filler storage and handling, part of the job at every inspector level. Checking that base metal and filler suit each other is part of the welding inspector level. In practice that means matching the heat number on the plate to its mill test report, the report to the specification on the drawing, and the filler to what the WPS lists.
The report lists the heat's chemistry and its mechanical test results, and that chemistry is where a carbon equivalent comes from when preheat is in question. The report also states the delivery condition, such as as-rolled, normalized, or quenched and tempered.
2.3.3Heat treatments and properties that get mixed up
- Preheat vs postweld heat treatment
- Preheat comes before the first pass and slows cooling. Postweld heat treatment (PWHT) comes after the weld is finished and changes stress or structure.
- Stress relief
- Heated below the lower critical temperature, held, and cooled slowly. You meet it as a PWHT entry on the WPS and PQR, with a time-and-temperature chart as the record.
- Normalizing
- Heated above the upper critical temperature and cooled in still air. You'll usually meet it as a plate's delivery condition on the mill test report.
- Tempering
- Reheating quench-hardened steel to a temperature below the lower critical. It's the second half of quenched-and-tempered plate, and the MTR says so.
- Hardness vs hardenability
- Hardness is how hard the steel is right now. Hardenability is how readily it hardens when cooled fast, the property that carbon equivalent tracks.
- Toughness vs ductility
- Toughness is energy absorbed in fracture, measured by Charpy impact tests. Ductility is how far the metal stretches before it breaks, shown by elongation and bend tests on destructive testing.
2.3.4Cooling, structure and heat treatment
Ferrous metallurgy at Part A depth. After this set, the CWI practice test mixes these tags in with every other area.
0 of 15 tagged · 0 accepted
Tag 01
What is the primary effect of increased carbon content on weldability?
Remarks on every option
- A Carbon doesn't improve fusion. It raises hardness and crack risk.
- B The opposite. More carbon makes steel harder to weld.
- C Carbon is the biggest single term in carbon equivalent, so it has a strong effect.
- D Correct: More carbon means a harder, more crack-prone HAZ, so weldability drops and preheat needs go up.
Pick an option. The remarks on all 4 open here.
Tag 02
How does section thickness affect cooling rate in welding?
Remarks on every option
- A Thickness changes how fast heat leaves the weld. Thicker sections cool faster.
- B Correct: A thicker section is a bigger heat sink, so the weld cools faster. That's why preheat needs rise with thickness.
- C Backwards. More metal pulls heat away faster.
- D Thickness affects distortion, but it also drives cooling rate, the bigger metallurgical issue.
Pick an option. The remarks on all 4 open here.
Tag 03
What effect does rapid cooling have on the ductility of low-alloy steel welds?
Remarks on every option
- A Rapid cooling doesn't add ductility, temporarily or otherwise.
- B Correct: Fast cooling can form hard, brittle structures like martensite in the HAZ, which cuts ductility.
- C Slower cooling helps ductility. Fast cooling hurts it.
- D Cooling rate is one of the main controls on HAZ properties.
Pick an option. The remarks on all 4 open here.
Tag 04
What temperature range is typically considered the critical range for carbon steel?
Remarks on every option
- A Correct: For carbon steel, the critical range runs from about 1333°F (lower critical) up to the upper critical, which depends on carbon content.
- B That's below the lower critical temperature. Carbon steel doesn't transform there.
- C That's well above the upper critical. The steel is fully austenitic there.
- D That's preheat territory, far below the critical range.
Pick an option. The remarks on all 4 open here.
Tag 05
What term describes the temperature below which a steel loses its ductility?
Remarks on every option
- A The lower critical is where austenite starts to form on heating. It has nothing to do with low-temperature brittleness.
- B Martensite start is where martensite begins to form on cooling. Different idea.
- C Stress relief is done hot to lower residual stress. It isn't where steel turns brittle.
- D Correct: Below the ductile-brittle transition temperature, steel breaks with little energy absorbed. Charpy impact testing finds it.
Pick an option. The remarks on all 4 open here.
Tag 06
Which property is most significantly affected by grain size in the weld metal?
Remarks on every option
- A Grain size has little effect on electrical conductivity.
- B Density barely changes with grain size.
- C Color isn't a mechanical property and doesn't track grain size.
- D Correct: Fine grains give better toughness. Coarse grains, often from high heat input, lower it.
Pick an option. The remarks on all 4 open here.
Tag 07
Which alloying element most significantly increases the hardenability of steel?
Remarks on every option
- A Copper adds strength and corrosion resistance but is a minor factor in hardenability.
- B Nickel helps hardenability and toughness, but far less than carbon.
- C Correct: Carbon has the biggest effect on how hard steel gets when it's cooled fast. That's why it dominates carbon equivalent.
- D Aluminum is a deoxidizer and grain refiner. It doesn't raise hardenability.
Pick an option. The remarks on all 4 open here.
Tag 08
What happens to the grain structure in the HAZ region closest to the fusion line?
Remarks on every option
- A Fine grains form farther out, where the HAZ just passed above the upper critical.
- B Correct: Right next to the fusion line the metal got hottest and the grains grew. That's the coarse-grained HAZ.
- C Grains don't disappear. They grow or refine with the heat.
- D This is the hottest part of the HAZ. It definitely changes.
Pick an option. The remarks on all 4 open here.
Tag 09
Which microstructure is typically considered the most brittle in steel welds?
Remarks on every option
- A Austenite is tough and ductile. Austenitic stainless steel is the everyday example.
- B Ferrite is soft and ductile.
- C Pearlite, a ferrite-carbide mix, is harder than ferrite but far tougher than untempered martensite.
- D Correct: Untempered martensite is the hardest, most brittle structure and the one behind hydrogen cracking in the HAZ.
Pick an option. The remarks on all 4 open here.
Tag 10
Which heat treatment process is most effective for grain refinement in carbon steel welds?
Remarks on every option
- A Tempering softens martensite and restores toughness but doesn't refine grains.
- B Age hardening is precipitation hardening for alloys like aluminum. It doesn't refine carbon steel grains.
- C Stress relief stays below the critical range, so the grains don't recrystallize.
- D Correct: Normalizing heats above the upper critical and air cools, which re-forms a finer, more uniform grain structure.
Pick an option. The remarks on all 4 open here.
Tag 11
What is the primary purpose of stress relief heat treatment after welding?
Remarks on every option
- A Stress relief stays below the transformation range, so grain structure doesn't change.
- B Stress relief doesn't harden. If anything, it softens slightly.
- C Correct: Postweld stress relief lowers the residual stresses left by weld shrinkage.
- D Some ductility may improve as a side effect, but the purpose is lower residual stress.
Pick an option. The remarks on all 4 open here.
Tag 12
What is the primary purpose of tempering after quench hardening?
Remarks on every option
- A Tempering is done below the critical range. It doesn't grow grains.
- B Correct: Tempering reheats quenched steel below the lower critical, trading a little hardness for much better toughness.
- C Tempering always gives up some hardness. That's the price of toughness.
- D Forming austenite takes heating above the critical range. Tempering stays below it.
Pick an option. The remarks on all 4 open here.
Tag 13
What is the primary effect of sigma phase formation in stainless steel welds?
Remarks on every option
- A Sigma phase ties up chromium, which hurts corrosion resistance.
- B Sigma is hard and brittle. It cuts ductility.
- C Any hardness gain comes with brittleness. Strength isn't the story here.
- D Correct: Sigma is a hard, brittle intermetallic that forms with long exposure at elevated temperature and embrittles the weld.
Pick an option. The remarks on all 4 open here.
Tag 14
At what temperature range does sensitization typically occur in austenitic stainless steels?
Remarks on every option
- A Correct: Around 800–1500°F, chromium carbides form at grain boundaries and leave chromium-depleted zones open to intergranular corrosion.
- B That's solution-annealing range. Carbides dissolve there.
- C Too low for carbide precipitation.
- D Too low. Sensitization needs much higher temperatures.
Pick an option. The remarks on all 4 open here.
Tag 15
Which of the following descriptions does NOT correctly apply to an electrode classified by AWS as E7018?
Remarks on every option
- A True of E7018. The 1 means all positions.
- B True. E7018 is a carbon steel electrode.
- C True. It runs a smooth, stable arc with little spatter.
- D Correct: This is the false statement. E7018 is a consumable SMAW electrode; GTAW uses a non-consumable tungsten electrode.
Pick an option. The remarks on all 4 open here.
2.3.5Straight answers on metallurgy
How deep does the metallurgy go on Part A?
Fundamentals level: carbon and low-alloy steel, what cooling does to them, and what each heat treatment is for. B5.1:2025 lists welding metallurgy fundamentals as a capability for the welding inspector and senior levels, not the associate level (AWS B5.1:2025, Table 5.1, checked October 2026). CAWI candidates still sit the same Part A, though.
Do I need to draw the iron-carbon diagram?
No. You need what it tells you: where the lower and upper critical temperatures sit, what happens to steel between them, and which heat treatments work above or below them.
Is stainless or aluminum metallurgy on Part A?
The Part A area is labeled ferrous in B5.1:2025. That covers stainless steels as well as carbon and low-alloy steel, so expect a little stainless. Aluminum isn't part of this area; D1.2, the aluminum structural code, is one of the Part C code choices instead.
Will Part C ask me for preheat temperatures?
If you chose D1.1, the minimum preheat and interpass requirements are in Clause 5 of either edition, but the 2025 edition renumbered the table. A table number from a prep book may send you to the wrong table. AWS lists both editions for Part C (AWS Exam References and Editions Guide, August 2025, checked October 2026), so confirm which one you're on in your confirmation letter.
Ten questions on a break
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