Department of Mechanical Engineering

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This research focuses on the effect of heat input of super duplex stainless steel (sDSS 2507) and nitronic steel (N50) dissimilar welded joints. Two heat input combinations selected as lower heat input (LHI) (0.62 kJ/mm) and higher heat input (HHI) (1.01 kJ/mm) were preferred during the operation of the gas tungsten arc welding process (GTAW) process using ER2594 filler. The macrosegregation like an island, peninsulas are observed in both weldments' HAZ and weld zone. The presence of secondary austenites (γ2) precipitation is observed in HAZ and root region of weldments. As heat input increases, the ferrite content of the weld zone in HHI decreases. Nevertheless, HHI had an advantageous effect on austenite nucleation in the HAZ. To ascertain the mechanical characteristics of the dissimilar metal welds (DMWs), tests such as the Vickers micro-hardness test, Charpy impact test, and tensile test were conducted. The mechanical evaluation reveals that the average hardness of LHI shows more hardness of 280 ± 4 Hv0.5 than HHI weldment of 270 ± 3 Hv0.5. Hence, weld zone, HAZ, and interface hardness do not indicate any significant change with the increment in heat input, which can be credited to the phase balance of ferrite/austenite. The tensile strength of LHI and HHI weldment is 895 ± 4 MPa and 900 ± 5 MPa, respectively, but LHI weldment displays better ductility. The Charpy impact test reveals that the impact toughness value decreases with increased heat input (i.e., 165 ± 5 J and 145 ± 3 J for LHI and HHI weldment, respectively) because of the secondary phase formation and increased grain size. However, the weld metal's Charpy impact toughness was more than the ASME standard value (&gt; 41 J) and the EN 1599:1997 standard value (&gt; 47 J). The microstructural observation and mechanical characterization suggest that lower heat input could be beneficial for weld’s structural integrity. © 2022, ASM International.

World University root node

Journal of Materials Engineering and Performance

Heat Input Effect on Dissimilar Super Duplex Stainless Steel (UNS S32750) and Nitronic Steel (N 50) Gas Tungsten Arc Weld: Mechanism, Microstructure, and Mechanical Properties

Application of phase-change material (PCM)-based compact heat exchanger for periodic cooling of electronic devices is widely employed due to its ability to store high thermal energy with isothermal operating characteristics and insignificant change in the volume while changing phase. The effect of change in refrigerant tube diameter on solidification phenomena in an ice freezing–type PCM-based heat exchanger was evaluated. A transient study for the effect of varying tube diameter on heat transfer characteristics was conducted using Ansys Fluent. The variation in tube diameter was considered for two cases, the first case where the total surface area has been kept constant and the second case in which the number of tubes remained constant. A parametric study to analyze the variation of heat flux and heat transfer coefficient was performed. Increasing the tube diameter reduced the time required for solidifying the ice. However, it would decrease the storage capacity of PCM in the heat exchanger with a significant increment in the refrigerant volume, which ultimately made the system bulkier and unfit for portable electronic equipment and also demanded more inventory. An optimum configuration that balances the solidification time along with the required capacity of PCM inside the system was obtained through the present numerical study.

Journal of Enhanced Heat Transfer

NUMERICAL STUDY OF TUBE DIAMETER EFFECTS ON SOLIDIFICATION OF PCM IN A COMPACT HEAT EXCHANGER

The present study focuses on dissimilar metal weld (DMW) of P91 ferritic-martensitic steel and Incoloy 800HT. The DMW was made nickel-based filler ERNiCrCoMo-1 filler using Tungsten Inert Gas (TIG) welding. Exhaustive microstructure analysis was done for the DMW. A stable austenitic microstructure was observed in the DMW solidified weld fusion zone (WFZ). Based on the peak welding temperature exposure in the different regions, the corresponding microstructure was observed to investigate the grain size transformations, phase transformations, diffusion, and segregation of constituent solute elements. Advance microstructure analysis was performed using Electron Probe Micro Analyzer (EPMA). Further, the effect of the observed microstructure feature on the mechanical property of the DMW was studied. The developed residual stresses were relaxed by post-weld heat treatment (PWHT). The tensile strength of the DMW was recorded less than the tensile strength of base metals. Also, impact toughness in as-welded (AW) WFZ was 117 J and reduced to 102 J after PWHT. Microhardness analysis showed maximum value in P91 heat-affected zone (HAZ) due to the dissolution of precipitates. It was reduced through tempering. The DMW of P91 and Incoloy 800HT was successfully produced without any major defect and with sufficient mechanical strength to put it in consideration for use in advanced ultra-supercritical (AUSC-Generation IV) boiler pipes and tubes as per the ASTM standards. © 2022

Journal of Manufacturing Processes

Investigation on joining P91 steel and Incoloy 800HT through gas tungsten arc welding for Advanced Ultra Super Critical (AUSC) power plants

Natural convection is a suitable method for thermal control because of its low cost, longevity, and convenience over a wide range of applications. It is suitable for the stances of low heat dissipation. The phenomenon of natural convection from horizontal heated surfaces is associated with various industries and equipment. The present study focuses on explaining the heat transfer by natural convection to a pool of water from an upward-facing heater surface. Stainless steel (SS 304) plates of different aspect ratios maintained under uniform heat flux conditions are considered for this study. An infrared (IR) camera is used to measure the surface temperature of the heater plates. The temperature distribution along the plate during the heat transfer process is analysed. Convection currents emerging during the process are visualized using the shadowgraph technique. This research puts light on the effects of aspect ratio, length, and width of the heater on heat transfer during the natural convection process. It is observed that the Nusselt number is independent of the aspect ratio. However, the length and width of the heater individually govern the heat transfer process. Independently increasing the length and width of the heater results in an increase in the Nusselt number. The experimental data of the present study are compared statistically with the existing correlations. An empirical correlation is suggested for analysing the natural convection heat transfer process. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

Heat and Mass Transfer/Waerme- und Stoffuebertragung

Heat transfer and fluid flow during natural convection on upward facing heater

In this article, a V-groove weld joint of P92 steel, typically used in ultra-supercritical power plants, has been numerically analyzed to estimate transient temperature distributions and residual stresses. A weld simulation model using Prescribed Temperature approach was developed. This approach was used to reduce the computational expenditure and speed up the time-intensive analysis setup. The finite element method was employed to compute the residual stresses generated in the weld region and the heat-affected zone along the thickness of the plate. In the experimental investigation, the through-thickness residual stresses were measured using the deep-hole drilling (DHD) method. Good agreement was observed between numerically and experimentally obtained residual stresses. The maximum temperature was observed at the weld pool area which decreased in the parabolic trend toward the base metal. © 2022, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Numerical Simulation of Temperature Fields and Residual Stresses in Multi-Pass Weld Using the Novel Prescribed Temperature Approach with Experimental Validation

In recent years pool boiling heat transfer has been a focus of study due to high heat dissipation capability corresponding to small temperature differences. The utilization of the aforementioned technique is widely implemented for thermal management in nuclear industries. This research primarily emphasises analysing the effect of length and diameter of tubes on bubble behaviour and CHF during pool boiling in saturated water under atmospheric pressure. The tubes are made of SS 304 and kept in a horizontal orientation. The tube diameters varied from 1.2 mm to 9 mm. The length of the tubes is varied from 50 mm to 1000 mm. It is observed that for the same length, lower diameter tubes exhibit a higher magnitude of CHF. For the same diameter, the smaller the length higher the CHF. The study shows that irrespective of diameter, beyond the length of 500 mm, CHF variation is insignificant. The study shows the nucleation and bubble behaviour for different dimensions of tubes under different heat fluxes. It is inferred from the experiment that for smaller curved surface areas, active nucleation sites are less. So, the bubble formation and coalescence are less. An empirical correlation, including the effect of tube length and diameter, is suggested for the pool boiling CHF. The experimental data are tabulated to contribute towards pool boiling CHF databank. © 2022 Elsevier B.V.

Nuclear Engineering and Design

Bubble behaviour and Critical heat flux on circular tubes during pool boiling process

The experimental study has been done to investigate the through thickness residual stress variation in P91/SS304H welds joint. The gas tungsten arc welding (GTAW) has been performed for joining of the dissimilar metal using the Ni-based ERNiCrMo-3 filler. The residual stress measurement was performed in the weld metal, SS304H HAZ and P92 HAZ. The results showed a considerable deviation in residual stresses along the thickness and in the transverse direction of the weldments. The PWHT showed a significant effect on magnitude and nature of the transverse and longitudinal residual stress for both weld metal and HAZ. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

A Study on Residual Stress Distribution in Welded Joint of P91 and SS304H Steel Plate

The present paper experimentally investigates the effect of filler metal on the mechanical behavior, solidification, and microstructure of the super duplex stainless steel (sDSS2507) and nitronic steel (N50) dissimilar welded joint. This dissimilar joint is primarily applicable in the subsea control unit for high-pressure tubing and coupler assembly. For this investigation, the gas tungsten arc welding process (GTAW) employed the super duplex filler ER2594 and carbon steel grade ER70S-2 filler. The weld's structural integrity has been assessed to compare both the fillers through multiple investigations on the joint. The microstructure characterization of the base metal and as-welded specimen was carried out using an optical microscope (OM) and scanning electron microscope (SEM). Super duplex filler ER2594 weld solidified in primary ferritic mode with precipitation of several reformed austenite in the ferrite matrix, whereas ER70S-2 filler weld had long martensite laths embedded in ferrite matrix. The microstructural study reported the presence of microsegregation and Type II boundary formation. The type-II boundary is detected close to the fusion boundary at the N50 and the sDSS 2507 side of the ER70S-2 weldment. The Vickers microhardness test, Charpy impact test, and the tensile test were performed to obtain the mechanical properties of this joint. The microhardness investigation of the weld zone of ER2594 and ER70S-2 shows the average hardness of 287.34 ± 10 Hv0.5 and 372.36 ± 10 Hv0.5, respectively. The peak hardness of 410 Hv0.5 was observed in the weld zone of ER70S-2. The formation of large martensite laths in the ferrite matrix in the weld zone leads to higher hardness in ER70S-2 filler compared to the precipitation of softer reformed austenite in the ER2594 filler. The average impact toughness result of ER2594 and ER70S-2 is 165 ± 5 J and 110 ± 8 J, respectively. The Charpy impact trials showed the ductile fracture mode by employing ER2594 filler, while ER70S-2 showed the mixed fracture mode (ductile–brittle). The weldment tensile strength of filler ER2594 and ER70S-2 is 897 MPa and 873 MPa, respectively. The tensile test results indicate the ductile fracture mode for both fillers, and the failures were detected in sDSS2507. © 2022, Wroclaw University of Science and Technology.

Archives of Civil and Mechanical Engineering

Effect of filler metal composition on microstructural and mechanical characterization of dissimilar welded joint of nitronic steel and super duplex stainless steel

The Friction Stir Welding procedure (FSW) is a promising approach for a variety of joined aluminum composites. However, using FSW in the welding of aluminum materials is a challenge. In recent years, there has been significant progress. Underwater friction stir welding (UWFSW) is a skilled procedure. It is a completely new and futuristic technology. The non-consumable tool runs over the substrate inside water without emitting any fumes in this method. There are several key advantages, including minimal distortion, a lack of liquefaction caused by imperfections, and excellent joining power. The quality of FSW joints in underwater is determined by factors such as tool rotational speed (TRS), tool transverse speed (TTS), tool tilt angle (TTA), and pin profiles. Each working parameter has a significant impact on joint strength. The purpose of this study is to examine the effect of UWFSW on the mechanical properties and microstructure characteristics of AA5083 armor-grade aluminum. In this work, one of the working characteristics is changed from the lowest to the highest level while the others remain constant. The joint formed from a straight hexagonal tool pin with a TRS of 1500 rpm, TTS of 40 mm/min, and TTA of 1° provided higher tensile strength and hardness than its counterparts due to the induction of stabilized material flow and the configuration of imperfection-free and perfect weld joints. © 2022, ASM International.

Mechanical and Microstructural Characteristics of Underwater Friction Stir Welded AA5083 Armor-Grade Aluminum Alloy Joints

The aim of the present work was to examine the microstructure and mechanical aspects of the Gas Tungsten Arc Welded dissimilar joint of P22 and P91 steel in as-welded (AW) and post-weld heat-treatment (PWHT) conditions. The weldments' optical and scanning electron microscopy characterization showed the heterogeneous microstructure formation along the weldments, which led to the variation in mechanical properties. After the PWHT, a carbon depleted soft and carbon enriched hard zone was observed near the interface of P22 steel and weld metal (WM) due to the diffusion of the carbon elements across the interface. A variation in hardness was observed along the weldments, and maximum was measured in WM (430 HV) and CGHAZ (408 HV) and reduced as move from the WM to base metal. A significant reduction in hardness of WM (333 HV) and CGHAZ (308 HV) was measured after the PWHT. Tensile strength of AW and PWHT conditions was measured 611 ± 9 MPa and 650 ± 13 MPa, respectively, which was higher than the tensile strength of P22 steel. The tensile test of the welded joint showed the failure in P22 steel base metal in AW and in P22 HAZ after PWHT, which indicates that welded joint is stronger than the base material. The impact toughness results also showed that the variation along the weldments and minimum impact toughness was measured 41 J in WM, which was lower than the impact toughness of the P22 and P91 base metal. The poor impact toughness of the WM was attributed to the untempered martensitic microstructure present in WM. In AW condition, maximum impact toughness of 184 J was measured in P22 HAZ; however, it was lower than the P22 base metal. The PWHT showed a significant increase in impact toughness of the WM and HAZ of P22 and P91 steel. © 2021, ASM International.