1. Every endeavor is a game, is it not? – Iblis Ginjo 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 Example - welds 304 stainless steel plate arc- welded to other plates Note corrosion in HAZ 304 stainless steel plate arc- welded to other plates Note corrosion in HAZ corrosion Why?

5. Corrosion Remember…. What makes stainless steel stainless? tight, tenacious film of Cr 2 O 3 on the surface film occludes electrolytes, oxygen Remember…. What makes stainless steel stainless? tight, tenacious film of Cr 2 O 3 on the surface film occludes electrolytes, oxygen

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

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

8. Ol' Harold's story 1913 We find Ol' Harold Brearley in England industriously testing alloy steels for gun barrels 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 Stolen from: Tales from Sheffield by Stan Lessteal Cutter Also see Brearley: Steel-makers; and Knotted String (EMS Library) Also see Brearley: Steel-makers; and Knotted String (EMS Library)

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

11. Suppressing corrosion Occlude electrolyte - coatings asphalt greases, oils paints polymers ceramic coatings "noble" metals 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 "noble" metals: unless scratch heals, a galvanic cell is set up

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

14. Suppressing corrosion Cathodic protection galvanizing: presence of scratch does not promote corrosion of protected metal 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 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 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 Assignment: Review today's classnotes a. weldments b. sensitization c. suppressing corrosion by coatings cathodic protection Read: pp 569-585