In stainless steel welding, what is sensitization and why is it important to minimize carbon pickup?

• A. Sensitization is carbide precipitation at grain boundaries that reduces corrosion resistance; minimized by minimizing carbon pickup and proper cleaning.
• B. Sensitization increases weld ductility.
• C. Sensitization improves corrosion resistance.
• D. Sensitization relates to color change.

Answer: (A)

Sensitization is the formation of chromium carbides at grain boundaries in stainless steel when heated in the welding heat-affected zone. This carbide precipitation pulls chromium away from the grain boundaries, leaving those boundaries chromium-depleted and therefore more susceptible to intergranular corrosion. The way to minimize sensitization is to limit carbon pickup—carbon atoms are what form those chromium carbides—by using low-carbon grades (like 304L/316L) and by controlling welding heat input to avoid long exposures in the sensitizing temperature range. Post-weld heat treatment or solution annealing can also dissolve carbides if needed. Cleaning helps prevent surface contaminants that could exacerbate corrosion, but the key control is reducing carbon content and heat exposure. The other statements aren’t accurate: sensitization does not increase ductility, it does not improve corrosion resistance, and it isn’t about color change.