Abstract:The effects of input heat of different welding processes on the microstructure, corrosion, and mechanical characteristics of welded duplex stainless steel (DSS) are reviewed. Austenitic stainless steel (ASS) is welded using low-heat inputs. However, owing to differences in the physical metallurgy between ASS and DSS, low-heat inputs should be avoided for DSS. This review highlights the differences in solidification mode and transformation characteristics between ASS and DSS with regard to the heat input in welding processes. Specifically, many studies about the effects of heat energy input in welding process on the pitting corrosion, intergranular stress, stress-corrosion cracking, and mechanical properties of weldments of DSS are reviewed.

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This paper develops a single order mathematical model for correlating various electrical discharge machining (EDM) parameters and performance characteristics by utilizing relevant experimental data obtained through experimentation. In addition to the effect of peak ampere, the effect of pulse on time and pulse off time on surface roughness has also been investigated. Experiments have been conducted on titanium alloy Ti-6Al-4V with a copper electrode retaining negative polarity as per the Design of Experiments. Response surface methodology techniques are utilized to develop the mathematical model as well as to optimize the EDM parameters. An analysis of variance has been performed for the validity test of fit and adequacy of the proposed models. It can be seen that increasing pulse on time causes a fine surface until a certain value, beyond which the surface finish deteriorates. The excellent surface finish is investigated in this study for the case of pulse on time below 80 µs. This result acts as a guide for selecting the required process outputs and most economic industrial machining conditions for optimizing the input factors.

Aluminum-stainless steel dissimilar welding processes yield unwanted disadvantages in the weld joint due to the large difference between the aluminum-stainless steel sheets' melting points and the nearly zero solid solubility between these two metals. Aluminum AA6061 and stainless steel SUS304 were lap-welded by using Metal Inert Gas (MIG) welding with aluminum filler ER5356 (Group 1) and stainless steel filler ER308LSi (Group 2). The effects of the welding voltage and type of filler metals used on the weld joints were studied. The welding voltage had a significant effect on the welding process, as higher voltage resulted in poorer appearance of the weld joint and led to defects for both groups, such as porosity and incomplete fusion. The microstructure for Group 1 joints shows enrichment of Si particles, which benefited the joint properties as it increased the strength of the metal. The stainless steel substrates that spread into the aluminum side are much greater in volume for Group 1 than for Group 2 joints. Meanwhile, the microstructure of Group 2 joints (using ER308LSi filler) consists of chromium carbide precipitation which yields a high hardness value, but a brittle structure. The hardness values of the welded seams in Group 1 and Group 2 range from 60 to 100 HV and 160 to 230 HV, respectively. The fracture in the tensile test yielded the highest tensile strength of 104.4 MPa with aluminum fillers. The tensile strength of Group 1 joints ranging from 47.8 to 104.4 MPa was collectively higher than Group 2 joints, between 20.24 to 61.76 MPa. Based on the investigation throughout this study, it can be concluded that the welding voltage of 18 V and aluminum filler ER5356 is the optimum filler in joining the dissimilar metals aluminum AA6061 and stainless steel SUS 304.

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Abstract:In this study, an attempt on pulsed-fiber laser welding on an austenitic-duplex stainless steel butt joint configuration was investigated. The influence of various welding parameters, such as beam diameter, peak power, pulse repetition rate, and pulse width on the weld beads geometry was studied by checking the width and depth of the welds after each round of welding parameters combination. The weld bead dimensions and microstructural progression of the weld joints were observed microscopically. Finally, the full penetration specimens were subjected to tensile tests, which were coupled with the analysis of the fracture surfaces. From the results, combination of the selected weld parameters resulted in robust weldments with similar features to those of duplex and austenitic weld metals. The weld depth and width were found to increase proportionally to the laser power. Furthermore, the weld bead geometry was found to be positively affected by the pulse width. Microstructural studies revealed the presence of dendritic and fine grain structures within the weld zone at low peak power, while ferritic microstructures were found on the sides of the weld metal near the SS 304 and austenitic-ferritic microstructure beside the duplex 2205 boundary. Regarding the micro-hardness tests, there was an improvement when compared to the hardness of duplex and austenitic stainless steels base metals. Additionally, the tensile strength of the fiber laser welded joints was found to be higher when compared to the tensile strength of the base metals (duplex and austenitic) in all of the joints.

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This paper presents the numerical study on two-dimensional forced convection heat transfer across three in-line flat tubes confined in a channel under incompressible, steady-state conditions. This system is solved in body-fitted coordinates (BFC) using the finite volume method (FVM). The constant heat flux is imposed on the surface of the tubes as the thermal boundary conditions. The range of the longitudinal pitch-todiameter ratio (S L /D s ) of 2.0-4.0 is considered, the Reynolds number varies within the range 25-300, and the Prandtl number is taken as 0.7. The temperature contours, local Nusselt number distributions at the tube surface and mean Nusselt number were analyzed. The strength of the heat transfer between the surface of the tubes and the air flow increases with an increase in Reynolds number and pitch-to-diameter ratio.