Carbide precipitation in stainless steels causes chromium depletion that affects the formation of what protective layer?

Carbide precipitation in stainless steels causes chromium depletion that affects the formation of what protective layer?

• A. The surface oxide layer
• B. The inner oxide layer
• C. The color oxide layer
• D. The etched oxide layer

Answer: (A)

Carbide precipitation at grain boundaries pulls chromium out of the nearby zones, leaving those areas chromium-depleted. Chromium is what forms the thin, protective chromium oxide film on stainless steel surfaces (the passive layer) that gives the metal its corrosion resistance. When chromium is withdrawn to form carbides, the surface can’t sustain that oxide film everywhere, especially near grain boundaries, so the protective layer is compromised. Therefore, the protective layer affected is the surface oxide layer (the passive chromium oxide film). The other terms don’t refer to this essential protective film.

Carbide precipitation at grain boundaries pulls chromium out of the nearby zones, leaving those areas chromium-depleted. Chromium is what forms the thin, protective chromium oxide film on stainless steel surfaces (the passive layer) that gives the metal its corrosion resistance. When chromium is withdrawn to form carbides, the surface can’t sustain that oxide film everywhere, especially near grain boundaries, so the protective layer is compromised. Therefore, the protective layer affected is the surface oxide layer (the passive chromium oxide film). The other terms don’t refer to this essential protective film.