1. Cooperative Research Centre for Welded Structures CRC-WS HACC For cracking to occur requires the simultaneous presence of: –Hydrogen –Applied stress –A susceptible microstructure

2. Cooperative Research Centre for Welded Structures CRC-WS Susceptible Microstructure Weld metal microstructure is not uniform: –Microscopic segregation –Macroscopic segregation lead to local variations in chemistry and potentially microstructure

3. Cooperative Research Centre for Welded Structures CRC-WS Crack in SMAW HSLA steel

4. Cooperative Research Centre for Welded Structures CRC-WS Crack in FCAW in HSLA steel, etched in Nital

5. Cooperative Research Centre for Welded Structures CRC-WS Crack in FCAW in HSLA steel, etched in Le Pera’s reagent

6. Cooperative Research Centre for Welded Structures CRC-WS X-ray map of Mn distribution in FCAW. White areas indicate highest concentrations.

7. Cooperative Research Centre for Welded Structures CRC-WS

8. Cooperative Research Centre for Welded Structures CRC-WS

9. Cooperative Research Centre for Welded Structures CRC-WS Crack in SAW in Q&T steel

10. Cooperative Research Centre for Welded Structures CRC-WS

11. Cooperative Research Centre for Welded Structures CRC-WS

12. Cooperative Research Centre for Welded Structures CRC-WS 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

13. Cooperative Research Centre for Welded Structures CRC-WS 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