AWS Certified Welding Inspector — FundamentalsWelding ProcessesHard
A CWI is evaluating a Weld Procedure Specification (WPS) for the repair of a thick-section carbon steel casting using Submerged Arc Welding (SAW). The WPS specifies a high heat input with a single electrode and DC+ polarity. What is the MOST significant metallurgical concern associated with this approach for thick-section carbon steel?
- AIncreased risk of hydrogen-induced cracking
- BFormation of hot cracks in the weld metal
- CReduced impact toughness in the HAZ
- DExcessive manganese burn-off
Show answer & explanationAnswer & explanation
Correct answer: C. Reduced impact toughness in the HAZ
High heat input, especially in thick-section carbon steel, leads to a slower cooling rate. This slower cooling rate results in coarser grain structures in the Heat-Affected Zone (HAZ) and weld metal, which significantly reduces the impact toughness, making the material more brittle, particularly at lower temperatures.
Why the other options are wrong
- A. Hydrogen-induced cracking is more associated with hydrogen presence and rapid cooling, not typically high heat input.
- B. Hot cracks are typically associated with weld metal chemistry and solidification patterns, rather than high heat input causing reduced toughness.
- D. Manganese burn-off is more related to arc stability and flux composition, not primarily high heat input.
SAW High Heat Input Effects
In Submerged Arc Welding, high heat input leads to slower cooling rates, which can coarsen grain structures and reduce mechanical properties, particularly impact toughness.
- Slower cooling rates in HAZ and weld metal.
- Coarsens grain structure (e.g., bainite, ferrite).
- Reduces impact toughness (Charpy V-notch energy).
- Increases residual stress and distortion.
- Can affect tensile strength and hardness.
Memory trick: Hot and slow makes it tough to take a blow.