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2 2024

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Probing the Thermal Stability and Microstructural-Mechanical Behaviour of Laser-Welded 17-4 PH Stainless Steel

Kumar Bikash, Sahu Ajit Kumar, Das Debtanay, Bag Swarup

Archives of Metallurgy and Materials

2024

Vol. 69, iss. 2

775--782

Dissimilar-weld-fabrications are created to capture privilege of certain attributes of each component to enhance the potential of overall structure. Induced residual stress owing to non-uniform thermal cycle, strain developed by virtue of metallurgical-transformation, and dramatic difference in thermo-physical and thermo-mechanical property, proved to be a major drawback and limits application certainly. Present study includes amalgamation of material-characterization and numerical-modelling to overcome aforementioned issue. The 17-4 precipitation-hardened steel was joined with SS316 steel by CO2 laser-welding technique using different-heat-input. It is noticed that the distribution and amount of δ-ferrite controls the on-site behavior relating to thermal stability, microstructural characteristics and residual stress generation. This work is attempted to understand thermal behavior as well as its correlation with δ-ferrite formation and residual stress distribution. Sequential-coupled-thermo-mechanical model proposed to developed for dissimilar weld joints at different process conditions. Finally, the interrelation between microstructure and the typical pattern of residual stress believed to be investigated systematically.

Phase transformation effect on residual stress development in fusion welding of dissimilar stainless steels with different thickness

Dwibedi Swagat, Kumar Bikash, Bag Swarup

Archives of Civil and Mechanical Engineering

2024

Vol. 24, no. 3

art. no. e148, 2024

The residual stress creates deleterious effects on joint properties of dissimilar welding due to differential thermophysical properties and mechanical constraints of dissimilar thickness. Accounting of solid-state phase transformation (SSPT) through the understanding of solidification behavior enhances the prediction accuracy of residual stress. The characterization of microstructural features improves the fundamental understanding of the residual stress evaluation. An attempt is made to comprehend the dependence of heat input on phase transformation and its effect on the generation of compressive residual stress in dissimilar welding. Three distinct heat inputs of 52, 63, and 77 J/mm are considered in micro-plasma arc welding (µ-PAW) of SS316L and SS310 with thicknesses of 800 µm and 600 µm, respectively. The measurement of residual stress is performed using the X-ray diffraction (XRD) method. The variation of δferrite from 11.2 to 7.9% is analogous to the variation of average δferrite lath size from 412 to 1040 nm, where inter-dendritic spacing varies from ~ 10 µm to ~ 20 µm. The solidification mode is identified as ferritic-austenitic (FA), which results in the formation of skeletal and lathy δferrite structures. Electron Backscatter Diffraction (EBSD) results show an increase in heat input leads to an increase in low-angle grain boundaries that results in a rise in the residual stress value. The phase fraction and residual stresses are computed employing a finite element (FE) based thermal-metallurgical-mechanical (TMM) model including the effect of SSPT. The reasonable agreement between the computed and experimental measurements with a maximum error of ~ 8.5% in weld size, ~ 7.5% in peak temperature, ~ 16% in retained δferrite, ~ 17% in residual stress, and ~ 5% in distortion demonstrates the reliability of the developed model. A lower level of heat input (52 J/mm) allows the formation of a high amount of δferrite, which generates comparatively more compressive stress as a disparity in thermal expansion coefficient aids in the reduction of residual stress.