Continuous Cooling Transformation (CCT) Diagrams for Advanced Navy Welding Consumables

摘要

We have characterized the transformation behavior and microstructural evolution of new ultra-low carbon (ULC) welding consumables being developed for Naval applications by the National Center for Excellence in Metalworking Technology (NCEMT). This is the first systematic study of these ULC alloys combining dilatometric analysis and transmission electron microscopy (TEM) with more conventional characterization techniques to identify in detail the microstructures produced at various cooling rates and develop continuous cooling transformation (CCT) diagrams for these new weld consumables. CCT diagrams of these NCEMT ULC alloys have been developed for (I) as-deposited weld metal from a weldinent of HSLA-lOO base plate welded with the 'CTC-OS' weld consumable and (11) weld rods representing the extreme rich and lean compositional variants expected for production quantities of the 'CTC-03' weld consumable. These results are compared to each other, to the results of our earlier examination of the HSLA- 100 base metal, and to the literature on some low carbon alloys. One of the important findings of this study is that the compositional variations expected from production heats cause extensive variations in the transformation behavior, microstructure, and microhardness of these ULC consumables. Since current fabrication practices would generate a similar compositional variation for any comparable ULC alloy, additional steps need to be taken to ensure the chemical homogeneity, and thus uniform weld properties, of the ULC weld consumables.