Please enable JavaScript.

Coggle requires JavaScript to display documents.

LOCALIZED (Microscopic) (Intergranular Corrosion (parts IGC (2.Knife line…

- - - - Attack at and adjacent to grain boundaries
      - Can be caused by impurities at grain boundaries, enrichment of alloying elements, depletion of element in grains boundary areas
      - small amount of iron in aluminium, where solubility iron low make it to segregate in grain boundary and cause intergranular corrosion
      - Depletion of chromium in grain boundary regions
    - - Pure iron, unstable by itself and want to corrode
      - chromium help to procrastinate nature attempts
      - Chromium in stainless steel alloy generally prevent corrosion
  - - - stabilized carbon react with Nb/Ti to form stable carbide. That why, Cr carbide formation not occur when it heated at critical temperature range.
      - Material that heated above 1230 degree during welding followed by rapid cooling make carbon atom remain in solid solution. If it were heated at critical temperature, localized sensitization were take place. The failure were happen by conventional IGC in narrow sensitized region
      - Occur for only a few grain diameter immediately to weld bead in stabilized austenitic
      - Preventing
        
        KLA : Heating above 815 degree to dissolve chromium carbide and to form Nb/Ti carbide at same time.
        
        IGC : Alteration of environment, Solution annealing, Use stabilized stainless steel, Chromium carbide will form but material is not sensitive to IGC
    - - Above 925 degree:
        
        Solubility carbon and nitrogen become significant in ferrite.
        
        IGC of ferritic cannot prevent by solution anneal and water quench or by reducing carbon below 0.03%
        
        Must soaked at 800 degree or slow cooled at 700 to 900 degree to replenish chromium depleted grain boundaries by diffusion to surrounding grains.
      - Duplex ss are complexly resistant to IGC. Cr are diffuses faster in ferrite compare in austenite at normal sensitizing temperature and carbide form at ferrite - austenite boundaries.
    - - Temperature between 815 degree and 425 degree:
        Carbide precipitate along grain boundaries leading to formation of chromium depleted zone around precipitated carbide
      - Below 425 degree :
        
        Cr depleted zone less corrosion resistant around grain.
        
        unfavorable area consist of large cathode and small anode.
        
        Diffusion rate of carbon atom low
        
        Carbide precipitation along grain boundaries cannot occur
      - Heating of austenitic will make sensitive to IGC