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Every endeavor is a game, is it not? – Iblis Ginjo

Every endeavor is a game, is it not? – Iblis Ginjo. Corrosion. Another type or micro cell - 2nd phase. 2nd phase will tend to react differently than matrix phase - sets up anode/cathode pair. Corrosion. Example - welds. Corrosion. corrosion. Example - welds.

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Every endeavor is a game, is it not? – Iblis Ginjo

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  1. Every endeavor is a game, is it not? –Iblis Ginjo

  2. Corrosion Another type or micro cell - 2nd phase 2nd phase will tend to react differently than matrix phase - sets up anode/cathode pair

  3. Corrosion Example - welds

  4. Corrosion corrosion Example - welds 304 stainless steel plate arc- welded to other plates Note corrosion in HAZ Why?

  5. Corrosion Remember…. What makes stainless steel stainless? tight, tenacious film of Cr2O3 on the surface film occludes electrolytes, oxygen

  6. Corrosion Corrosion in stainless steel HAZ due to "sensitization"

  7. Corrosion Decrease C content - no Cr carbide formation Tie up C as Ti carbide (321) or Nb carbide (347) - no Cr carbide formation How to avoid sensitization – get rid of C

  8. Ol' Harold's story 1913 We find Ol' Harold Brearley in England industriously testing alloy steels for gun barrels

  9. Ol' Harold's story Ol' Harold's records showed that the unrusted steel sample contained 14% Cr! The birth of stainless steels! Moral: behind every successful person, there may be a junk pile Stolen from: Tales from Sheffield by Stan Lessteal Cutter Also see Brearley: Steel-makers; and Knotted String (EMS Library)

  10. Suppressing corrosion Components of a cell: anode cathode electrolyte connection

  11. Suppressing corrosion Occlude electrolyte - coatings asphalt greases, oils paints polymers ceramic coatings "noble" metals

  12. Suppressing corrosion Occlude electrolyte - coatings "noble" metals: unless scratch heals, a galvanic cell is set up

  13. Suppressing corrosion Cathodic protection galvanizing: Zn coating applied by hot-dipping electroplating

  14. Suppressing corrosion Cathodic protection galvanizing: presence of scratch does not promote corrosion of protected metal but steel helps Zn corrode

  15. Suppressing corrosion Cathodic protection set up cell by adding metal which is more anodic than metal or alloy to be protected

  16. Suppressing corrosion Cathodic protection example: protecting ship plate

  17. Assignment: Review today's classnotes a. weldments b. sensitization c. suppressing corrosion by coatings cathodic protection Read: pp 569-585

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