University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Microstructures in (High Strength) Steel Welds

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Aim To determine –A relationship between microstructure and crack path –The effect of chemical composition on propensity to crack

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Procedure Two parallel strands: –Experimental – Examination of Weld Microstructures –Simulation - Aachen.

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Microstructure – Literature Review HAZ cracking can be reasonably predicted by calculation of hardness using CE, P cm etc. values CE, P cm values are not a good guide for the calculation of weld metal susceptibility because hardenability appears to be an important parameter

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Microstructure - Literature Review High strength weld metals contain localised variations in hardness of 50– 80HV 5

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS 250x Experimental Result

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Experimental Result

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Experimental Result Local variation of microstructures controls location of cracks in multi-pass welds Most of the cracks are densely populated in the microstructural region of higher hardness.

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Experimental Result

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Microstructure - Literature Review In most cases cracking originates at a point between 0.1 and 0.3 of the plate thickness when measured from the top of the plate, regardless of the plate thickness. This is usually immediately below the second or third to last runs. Region of the highest H D levels Region of highest residual stress

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Experimental Result

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Microstructure – Literature Review The appearance of hydrogen cracked fracture surfaces may be either brittle (cleavage) or ductile (dimpled).

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Experimental Result Region close to the initiation point

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Experimental Result Region some distance from the initiation point

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Microstructure – Literature Review Cracking may have a relationship with grain boundary ferrite and former austenite grain boundaries but the correlation is uncertain. More detailed metallographic research required to relate microstructure and crack path

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Simulation - Aachen Use directional solidification of the alloy compositions of interest. Identify the compositions of the phases formed. Determine how the elements are partitioned. Determine the segregation ratios of the elements. Compare the outcomes with micro-hardness and x-ray analysis results from weld samples.

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Summary The appearance of the fracture surface close to the point of initiation has been found to be consistent for all cases studied i.e.: –Hydrogen charged weld sample form DSTO –Weld sample from ??? –FCAW and GTAWsamples from two MSc students –Multi-run sample from D. Nolan/M. Pitrun

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Modelling of Hydrogen Methodology Jointly, with the Foundry Institute of RWTH Aachen endeavor to integrate the software packages; MICRESS – simulation software which can predict crystal growth and phase transformations from thermodynamic data whilst taking into account micro-segregation with CASTS – simulation software for the weld morphology and macro-segregation

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Modeling of Hydrogen

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Modeling of Hydrogen – Literature Review Diffusible hydrogen is considered to be the cause of hydrogen-assisted cold cracking in welds and is associated with reversible traps. Residual hydrogen is term for permanently trapped hydrogen atoms in irreversible traps sites. Traps include the host lattice, vacancies, solute atoms, dislocations, grain boundaries, voids, and second phase particles (inclusions).

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Models of Hydrogen Cracking– Literature Review hydrogen enhanced decohesion (HEDE) which hereby describes the decrement in lattice interaction energy due to the accumulation of hydrogen with the aid of triaxial stress,

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Aim To model the distribution of hydrogen concentrations present in a double “v” butt weld. ANSYS will be used as the modelling package.

University of Adelaide -Cooperative Research Centre for Welded Structures CRC-WS Hydrogen Model Diffusible hydrogen H D is a maximum at 0.75 – 0.9 of plate thickness regardless of plate thickness Repetitive thermal cycling and weld bead overlapping determine the final local H D concentration Crack density increases in the same manner with cracks predominately located below the second or third weld beads from the surface. This point also coincides with maximum residual stress level