AWS Certified Welding Inspector — FundamentalsWelding MetallurgyMedium
A welding inspector is observing the welding of a structural component made of 304 stainless steel. The welder is using a high heat input process without proper interpass temperature control. What type of metallurgical phenomenon is most likely to occur in the heat-affected zone (HAZ) of the stainless steel due to this practice?
- AMartensitic transformation
- BSpheroidization
- CSensitization
- DGraphitization
Show answer & explanationAnswer & explanation
Correct answer: C. Sensitization
High heat input and improper interpass temperature control can lead to prolonged exposure of the HAZ to temperatures in the sensitization range (425-870°C, or 800-1600°F), causing chromium carbides to precipitate at grain boundaries and deplete adjacent regions of chromium, making the steel susceptible to intergranular corrosion (sensitization).
Why the other options are wrong
- A. Martensitic transformation does not occur in 304 (austenitic) stainless steel; it's characteristic of hardenable steels.
- B. Spheroidization is a process to soften steel by forming spherical carbides, not a primary concern or adverse effect of welding 304 stainless steel.
- D. Graphitization is a concern in carbon and low-alloy steels at high temperatures over long periods, not typically in stainless steels.
Sensitization in Stainless Steel
A metallurgical phenomenon in austenitic stainless steels where chromium carbides precipitate at grain boundaries due to exposure to specific temperatures (425-870°C), depleting adjacent areas of chromium and rendering them susceptible to intergranular corrosion.
- Occurs in austenitic stainless steels (e.g., 304, 316).
- Triggered by heating in the 425-870°C (800-1600°F) range.
- Leads to chromium depletion near grain boundaries.
- Results in susceptibility to intergranular corrosion ('weld decay').
Memory trick: High heat makes stainless steel 'Sense' the corrosion.