This study presents results of experimental tests on quality of dissimilar welded joints between 316L austenitic and 2304 lean duplex stainless steels, welded without ceramic backing. Fiber laser welded butt joints at a thickness of 8 mm were subjected to non-destructive testing (visual and penetrant), destructive testing (static tensile test, bending test, and microhardness measurements) and structure observations (macro- and microscopic examinations, SEM, element distribution characteristics, and ferrite content measurements). Non-destructive tests and metallographic examinations showed that the welded joints meet the acceptance criteria for B level in accordance with EN ISO 13919–1 standard. Also the results of the destructive tests confirmed the high quality of the joints: specimens were fractured in base material with lower strength—316L austenitic stainless steel and a 180° bending angle was obtained confirming the high plasticity of the joints. Microscopic examination, SEM and EDS analysis showed the distribution of alloying elements in joints. The microhardness of the autogenous weld metal was higher by about 20 HV0.2 than that of the lean duplex steel. Ferrite content in the root was about 37% higher than in the face of the weld. The Schaeffler phase diagram was used to predict the phase composition of the welded joints and sufficient compliance with the magnetic method was found. The presented procedure can be used for welding of 316L–2304 stainless steels dissimilar welded joints of 8 mm thickness without ceramic backing.

In this article, the mechanical properties and microstructure of 304L austenitic stainless steel/Incoloy 800HT nickel alloy dissimilar welded joints are investigated. The joints were made of 21.3 mm × 7.47 mm tubes using the TIG process with the use of S Ni 6082 nickel filler metal. No welding imperfections were found and high strength properties of joints were obtained, meeting the assumed acceptance criteria of the product’s standards. The tensile strength of the welded joints was higher than for the joined materials (Incoloy 800HT). Macro- and microscopic metallographic tests revealed the correct morphology of the joints and the appropriate structures in their critical zones. However, differences were found in the morphologies of the zones between the weld and the base materials. In fusion boundary from the side of the Incoloy 800HT alloy, no clear outline of the fusion line was observed (type A fusion boundary), while increased grain size and an epitaxial structure were observed. In turn, in the zone: weld–304L steel, a distinct fusion line was observed with areas with an increased amount of high-temperature δ ferrite (type B fusion boundary). No precipitates were found that could reduce the resistance of the joints to intergranular corrosion. A hardness decrease (approximately 30 HV0.1) in the transition zone: austenitic steel–weld and an increase of hardness (approximately 10 HV0.1) on the opposite side of the welded joint were observed.

This article deals with the dissimilar joining of two different grade Cr-Mo steel (2.25Cr-1Mo: P22 and modified 9Cr-1Mo: P91) for power plant application. The dissimilar butt-welded joint was produced for conventional V groove design by using the gas tungsten arc welding (GTAW) process with the application of an ERNiCrMo-3 Ni-based super alloy filler. A microstructure characterization was performed to measure the inhomogeneity in the microstructure and element diffusion across the interface in a welded joint. The experiments were also performed to evaluate the mechanical properties of the dissimilar welded joint in as-welded (AW) and post-weld heat treatment (PWHT) conditions. An acceptable level of the mechanical properties was obtained for the AW joint. After PWHT, a significant level of the element diffusion across the interface of the weld metal and P22 steel was observed, resulting in heterogeneity in microstructure near the interface, which was also supported by the hardness variation. Inhomogeneity in mechanical properties (impact strength and hardness) was measured across the weldments for the AW joint and was reduced after the PWHT. The tensile test results indicate an acceptable level of tensile properties for the welded joint in both AW and PWHT conditions and failure was noticed in the weak region of the P22 steel instead of the weld metal.

A dissimilar welded joint of Inconel 718 and 304L austenitic stainless steel was prepared using a combined procedure with the gas tungsten arc welding and shielded metal arc welding processes by employing the Ni-based fillers: ERNiCr-3 and ENiCrFe-3. The welded joints were investigated for metallographic testing and mechanical properties, and a relationship was established between the microstructure and the resultant mechanical properties. Microstructural observation revealed the formation of the unmixed zone on the 304L SS side. The weld metal showed that the fully austenitic microstructure consisted of the Nb- and Ti-rich carbide phases along the inter-dendritic spaces. The tensile test results at room temperature showed the failure from the weld metal which might be due to alloying element segregation along the inter-dendritic spaces. However, a tensile test at 600 °C showed the failure from the 304L SS base metal with a tensile strength and % elongation value of 377 MPa and 24%, respectively. The hardness plot showed the average hardness value of the weld metal of 236 ± 5 HV, which was higher than the 304L SS BM (204 ± 4 HV) but lower than the IN718 BM (243 ± 5 HV). The impact toughness of the weld metal was 109 J, which was significantly lower than the base metals. The poor impact strength of the weld metal might be due to the evolution of the NbC phase along inter-dendritic spaces.

In this paper are characterized problems of high strength steel weldability in underwater wet welding conditions. Water as a welding environment intensifies action of unfavourable factors which influence susceptibility to cold cracking of welded steel joints. The susceptibility to cold cracking of S355J2G3 steel and S500M steel in wet conditions was experimentally estimated (by using Tekken test). It was concluded that the steels in question are characterized by a high susceptibility to formation of cracks in welds. Usefulness of the proposed Temper Bead Welding technique (TBW) was experimentally verified as a method for improving weldability of the steels in the analyzed conditions.