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HACC

HACC. For cracking to occur requires the simultaneous presence of: Hydrogen Applied stress A susceptible microstructure. Susceptible Microstructure. Weld metal microstructure is not uniform: Microscopic segregation Macroscopic segregation

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HACC

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  1. HACC • For cracking to occur requires the simultaneous presence of: • Hydrogen • Applied stress • A susceptible microstructure

  2. Susceptible Microstructure • Weld metal microstructure is not uniform: • Microscopic segregation • Macroscopic segregation lead to local variations in chemistry and potentially microstructure

  3. Crack in SMAW HSLA steel

  4. Crack in FCAW in HSLA steel, etched in Nital

  5. Crack in FCAW in HSLA steel, etched in Le Pera’s reagent

  6. X-ray map of Mn distribution in FCAW. White areas indicate highest concentrations.

  7. Crack in SAW in Q&T steel

  8. Summary • Micro-segregation appears to occur on the cellular dendritic boundaries • Micro-segregation of all elements appears to be in the same ratio of 1.4:1 • The micro-segregated region is harder than the matrix by the order of 100Hv • The crack path is through the intercellular dendritic micro-segregated harder regions

  9. Proposed UoA Work • Quantify the role of segregation on weld metal susceptibility to HACC • Expand hydrogen diffusion model to consider hydrogen segregation • Investigate the parameters that determine whether a HACC microcrack propagates to be significant • Contribute segregation and hydrogen diffusion strands to the overall model of weld metal HACC

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