| Abstract Scope |
Introduction: In gas metal arc welding (GMAW) of shipbuilding steels, small silicate islands appear on the weld deposit surface. These silicate islands must be removed prior to any multipass welding or painting operations. The time required to clean these islands negatively impacts both cost and schedule. New GMAW electrode technology must be developed and implemented to result in silicate-free weld deposits with acceptable visual and mechanical properties.
The silicon in GMAW filler metal improves both weld pool fluidity during fusion as well as weld pool deoxidization during solidification. Lean argon – carbon dioxide (CO2) gas mixtures are preferred for high quality weldments during shipbuilding. These shielding gas mixtures allow for improvement of weld pool wetting through the additions of oxygen from the CO2 as well as spatter-free metal transfer with the assistance of modern waveform power supplies. When welding shipbuilding steels, military specification grade GMAW electrodes are designed provide both preferred fusion welding performance as well as resultant weldment properties. A drawback of these electrodes is the presence of silicate islands on the top of the weldment that must be removed prior to subsequent welds or a paint process.
New GMAW electrodes have been developed for lean CO2 shielding gas mixtures and have shown to produce sound weld deposits in single-wire fillet welding applications outside of the shipbuilding industry. These electrodes need be evaluated for multipass tandem GMAW groove welding to improve shipbuilding productivity and affordability.
Experimental Approach: This project will test and evaluate the properties of V-groove butt joints using two thicknesses of HSLA-65 base material. Welding parameter development will use both the new silicate-free electrode as well as a legacy ER70S-6 electrode to provide a baseline for comparison purposes. Welding development will use both minimum and maximum heat inputs to provide a wide operating window for welding process implementation. For each wire, plate thickness, heat input, weld transfer characteristics, and resultant weld bead surface quality will be captured to allow for comparison. During parameter development, each parameter set will be nondestructively evaluated in accordance with MIL-STD-271F (Requirements for Nondestructive Testing Methods) and destructive testing in accordance with NAVSEA Technical Publication S9074-AQ-GIB-010/248 (Tech Pub 248). In addition to the requirements presented in Tech Pub 248, microhardness and microstructure evaluations will be conducted to better understand the impact of the absence of silicon.
Results and Discussion: Work for this project recently kicked off; results will be ready to be shared by the time of the AWS Professional Program.
Conclusions: Work on the current project is not complete and conclusions based on this work will be included in the final presentation.
Acknowledgements: This work is funded by the National Shipbuilding Research Program (NSRP) and Huntington Ingalls – Ingalls Shipbuilding and Naval Surface Warfare Center – Carderock Division provided guidance and assistance. |