Abstract
The present study aims at investigating bead geometry and the evolution of microstructure with thermal cycles in multipass shielded metal arc welding of a V-groove 13-mm type-2507 super-duplex stainless steel (SDSS) plate. The weld consisted of 4 beads produced with arc energies of 0.81–1.06 kJ/mm. The upper beads showed lower base metal (BM) dilution than the first bead. Thermal cycles were recorded with thermocouples, indicating that the cooling rate decreased in the as-deposited weld zone when adding a new bead. Ferrite fraction in the as-welded condition was lower for the upper beads. The austenite grain morphology in reheated passes varied depending on the local peak temperatures and the number of reheating passes. Sigma phase precipitated in a location reheated by the third and fourth passes that was subjected to a critical peak temperature for sigma precipitation. Ferrite content, measured using image analysis and Fisher FERITSCOPE technique, showed that the ferrite fraction moved toward 50/50% in the weld metal with an increasing number of reheating cycles. Finally, a schematic map showing an overview of the microstructure in the multipass SDSS weld was introduced.
Highlights
Duplex stainless steels (DSS), with a ferritic-austenitic microstructure, provide an excellent combination of high corrosion resistance and good mechanical properties [1]
The first bead was fabricated with slightly lower arc energy and 3.5-mm dimeter electrode aiming at having better control of the weld
The welding parameters, thermal cycles, weld pool geometry, dilution, microstructure and ferrite fraction evolution were studied for multipass shielded metal arc welding of a 13-mm V-grooved type 2507 plate
Summary
Duplex stainless steels (DSS), with a ferritic-austenitic microstructure, provide an excellent combination of high corrosion resistance and good mechanical properties [1]. Super-duplex stainless steels (SDSS), containing a higher content of alloying elements compared with lean and standard DSS, are used in harsher corrosive environments [2]. It has been claimed that an equal fraction of ferrite and austenite provides the best combination of properties in DSS [3], which is normally difficult to achieve during final fabrication such as welding. The precipitation of secondary phases is another challenge during the fabrication of DSS, in SDSS with a higher content of alloying elements [4, 5]. The situation is more complicated in multipass welds and wire-based additive manufacturing, as different locations in the material experience multiple thermal cycles with different peak temperatures [9]
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