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Evaluation of microstructural and mechanical qualities in optimised TIG-welded SDSS 2507 joints

Kumar Sujeet, Srinivas Madugula Naveen, Kumar Naveen, Giri Jayant, Fatehmulla Amanullah

Materials Science Poland

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2024

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Vol. 42, No. 4

163--179

EN

Super duplex stainless steel (SDSS) is gaining attraction owing to its excellent mechanical strength and superior corrosion resistance. In this study, tungsten inert gas (TIG) was implemented for welding the SDSS thin sheet. The Taguchi method and analysis of variance (ANOVA) were carried out by selecting L25 orthogonal arrays. The optimum TIG parameters were a welding current of 75 A, an arc potential of 15 V, a welding rate of 120 mm/min, and an argon gas consumption rate of 12 L/min. An ANOVA study found that welding current (46.95%) was the largest contributor in producing the excellent welded joint. The microstructural research indicated increased grain size in the heat-affected zone (HAZ) and fusion zone (FZ), represented by distinct grain boundary layers, intragranulars, and Widmanstätten austenite. This was due to heat input and rapid cooling inclusion as well as re-crystallisation of the ferrite matrix. The elemental mapping analysis showed that chromium must be present to generate a shielding oxide layer, which decreased from 25.50% in the parent material to 23.40% in the TIG welded joint. The tensile test found that TIG welds had an ultimate tensile strength (UTS) of 789 MPa. This value was equivalent to the base metal UTS value of 800 MPa. The micro-hardness test of the TIG welded joint confirmed that the HAZ (350 HV) and FZ (325 HV) were higher than that of the base metal (305 HV). The hardness value near the FZ boundary experienced a significant increase due to the development of hard microscopic components and element migration during the TIG process.

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Tribological performance of gas tungsten arc welded dissimilar joint of sDSS 2507/IN‑625 for marine application

Maurya Anup Kumar, Khan Waris Nawaz, Patnaik Amar, Adin Mehmet Şükrü, Chhibber Rahul, Pandey Chandan

Archives of Civil and Mechanical Engineering

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2024

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Vol. 24, no. 1

art. no. e23, 2024

EN

The present study utilizes a slurry-pot wear tester to investigate the relationship between slurry concentration and slurry-erosion performance of sDSS 2507/IN625 dissimilar weld joint (DWJ). Varying slurry concentrations (10 and 30 wt.% silica sand) were utilized to investigate erosion, weight loss, and wear mechanisms in severe environments. The study aimed to provide an in-depth knowledge of erosion behaviors by analyzing surface characteristics, microstructure characteristics, and material removal mechanisms. The electron probe micro-analyzer studied weld zone element segregation and scanning electron microscopy (SEM) examined microstructure and erosion mechanism. ER2594 filler weld shows higher microhardness as compared to weld fabricated using ERNiCrMo-3 filler metal. Sand particle density, particle-to-surface contact, particle interactions, and fluid impacts increase cumulative weight loss and decrease erosion rate per unit solids weight. Slurry concentration increased weight loss by 23% for sDSS 2507 BM and 33% for IN-625 BM. ER2594-LHI lost 72% and ERNiCrMo-3-LHI 77% more weight with increasing slurry concentration. Filler ERNiCrMo-3 has less erosion wear than filler ER2594 as the concentration of slurry increases. SDSS 2507 BM and IN-625 BM erode 1.45 and 1.8 times faster with increasing slurry concentration, respectively. The erosion rate of ER2594-LHI and ERNiCrMo-3-LHI increases 0.85 and 1.2 times with slurry concentration. SEM analysis of the worn surface exhibits mixed cutting–ploughing modes coexisting with the formation of craters. The material removal has predominantly occurred from the cutting and ploughing mechanism, whereas the characteristic presence of craters and frontal and lateral lips is also found across the entire surface. The results from this study suggest the optimum heat input to be maintained during weld fabrication of sDSS 2507/IN-625 using ER 2594 and ERNiCrMo-3 filler metals for enhanced resistance against slurry erosion wear. Also, an insight into the wear mechanism helps in understanding the effect of microstructural features on the wear performance of welds in operational conditions.

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Structure–property relationship assessment of dissimilar gas tungsten arc welded joint of pipeline steel and super duplex stainless steel for marine applications

Maurya Anup Kumar, Kumar Naveen, Pandey Chandan, Chhibber Rahul

Archives of Civil and Mechanical Engineering

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2024

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Vol. 24, no. 3

art. no. e164, 2024

EN

This study investigates the structure–property relationship in a dissimilar joint between super duplex stainless steel (sDSS 2507) and pipeline steel (X-70) using gas tungsten arc welding and ER2594 filler. Tubing and risers used to transport hydrocarbons are regularly joined using these dissimilar metals. The microstructures of lower heat input (LHI-0.7 kJ/mm) and higher heat input (HHI-1.4 kJ/mm) weldments were examined to understand the influence of heat input on the structure–property relationship. The weldments' mechanical characteristics were tested via hardness, impact, and tensile tests. Base metal and weld zone/interface characterization were studied utilizing optical and scanning electron microscopes with energy-dispersive spectroscopy (EDS). Elemental variation was confirmed by EDS spectra, elemental line mapping, and electron probe microanalysis with wavelength-dispersive spectrometer along the weld interface and weld zone. Significant microstructure variation was observed in X-70 BM at the LHI and HHI weld interfaces. Type II boundary and macro-segregation forms like peninsulas and islands were present in both weldments. In LHI and HHI weldment, duplex microstructure dominates the weld zone cap and filler pass. In the backing pass, duplex microstructure replaces skeletal ferrite, which predominates in the root pass of the HHI weld zone. LHI weldment has an average microhardness of 275 ± 7 HV0.5, while HHI had 285 ± 5 HV0.5. Both weldment’s tensile tests revealed that the sample fractured on the weaker X70 BM side. LHI and HHI weldments had 600 MPa and 610 MPa ultimate tensile strengths and 22% and 18% elongation percentages, respectively. LHI weldments (200 ± 7 J, 210 ± 4 J) and HHI weldments (210 ± 5 J, 220 ± 8 J) have lower average impact toughness in cap and root pass than the sDSS 2507 BM (320 ± 3 J) and X-70 BM (300 ± 6 J), respectively. The increase in heat input led to a minimal 2% difference in tensile strength, a notable 10% increase in hardness, and a slight 5% variation in impact toughness between LHI and HHI weldments. Marine and offshore applications may benefit from investigating the sDSS 2507/X-70 DWJ's process parameter selection, thermodynamic analysis, and structure–property relationship.