Corrosion cheat sheet

Corrosion problems with 300 series stainless steel 19-05 

Types of Corrosion with 300 series stainless steel

• Chloride Stress corrosion.
  • Four things necessary. The exact percentage of each is unknown
    • The presence of chlorides (There are more chlorides in this world than any other chemical)
    • 300 series stainless steel. (The most popular)
    • Corrosion slows down below 40В°F (5В°C) and above 285В°F (140В°C.)
    • Tensile stress.
  • What happens?
    • Forms Cr₂O₃ on metal surface. This is called pacification,
• Concentrated cell or crevice corrosion
  • Salt water is low in Ph (8.0 to 9.0) and high in chlorides
• Erosion/ corrosion
  • Fluid movement removes the protective oxide layer exposing the softer stainless steel.
• Fretting corrosion
  • Rubbing removes the protective oxide layer
• Galvanic corrosion
• General corrosion
  • Doubles each 10В°C (20В°F )rise in temperature
• Intergranular
  • At 1050В°F (565В°C) to 1600В° F(870В°C) Carbon in steel combines with the chrome to form chrome carbide.
  • This is a normal welding temperature.
  • Fix
    • Anneal the piece after welding to remove stress.
    • Use low carbon type stainless steel.
    • Add columbium to form columbium carbide. Metal is said to be stabilized.
• Micro organisms
  • Aerobic, the kind that need oxygen.
  • Anaerobic, the kind that do not need oxygen.
  • Facultative, the type that goes both ways. They operate with or without oxygen
• Pitting
• Selective leaching
• Zinc embrittlement