🔹 Chromium (Cr)
Primary Role: Corrosion resistance (passive film formation at >10.5%), hardenability improvement
Key Point: Forms chromium carbides which can cause intergranular corrosion if precipitated at grain boundaries
🔹 Nickel (Ni)
Primary Role: Toughness at low temperatures, austenite stabilization
Key Point: Lowers ductile-to-brittle transition temperature without loss of ductility
🔹 Molybdenum (Mo)
Primary Role: Hardenability, pitting corrosion resistance, high-temperature strength
Key Point: Forms stable carbides at high temperatures, prevents temper embrittlement
🔹 Ni-Cr-Mo Combination
Primary Role: Balanced strength, toughness, and corrosion resistance
Key Point: Ideal for pressure vessels and offshore structures
⚠️ Common Traps
• Chromium carbides vs corrosion resistance
• Nickel improves ALL corrosion (FALSE!)
• High Cr always good (can cause delta ferrite brittleness)
• Confusing hardenability mechanisms
💡 Interview Keywords
• "Passive film" (Cr)
• "FCC stabilization" (Ni)
• "Delays transformation" (Mo)
• "Creep-resistant carbides" (Mo)
• "Intergranular corrosion" (Cr carbides)