Heat Input Conditions Research Articles

Effects of Heat Input Conditions on the Local Thermophysical Properties of Super Duplex Stainless Steels

The thermal properties of the super duplex stainless steels are strongly affected by the thermal history when welding procedure are applied leading to substantial changes on the mechanical properties of the welding region. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this research a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure is developed. The model was verified by measured temperature profile and used to predict local properties such as grain size evolution, hardness and mechanical strength. An inverse method was implemented to obtain the parameters fitting for the grain growth evolution, hardness and yielding strength compatible with the final microstructure and grain size measured using SEM images and stereological techniques.

Comprehensive Analysis of TIG Welded Inconel–718 Alloy for Different Heat Input Conditions

In this research, the effects of heat input on tensile properties and microstructure were investigated for super alloy Inconel-718 sheets weld by Tungsten Inert Gas (TIG) welding process. The tensile properties and microstructure of weld joints were evaluated. The experiment was conducted with six different combinations of welding parameters like welding current, voltage and welding speed, which were give in six different welding heat input combinations of welding parameters. The experimental results shows that the welding joints weld with low welding heat input was yield higher tensile properties. From the experimentation it was understand that the tensile properties increases when the welding heat input decrease. Drastic grain coarsening was evidenced when the heat input was increases. For the weld joints experimented in this research it was also observed that amount of laves phase was increased with increase in the welding heat input which is the major fact for noticeable variation in the ultimate tensile strength of the weld joints welded by TIG welding process with different welding heat input.

A Comparative Study of the Heat Input During Laser Welding of Aeronautical Aluminum Alloy AA6013-T4

The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 μm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features.

Metal transfer in wire feeding-based electron beam 3D printing: Modes, dynamics, and transition criterion

In electron beam three-dimensional (3D) printing, the metal-transfer behaviors play significant roles in determining the quality of the end product; however, these mechanisms have not yet been well understood. In the present study, we performed plenty of experiments and novel modeling of the wire feeding based electron beam 3D printing to reveal the metal-transfer mechanisms in depth. The coupling behaviors of the heat transfer and the fluid flow in the molten pool as a function of the process parameters in the electron beam 3D printing of the Ti–6Al–4 V alloys were simulated. The simulation results reasonably agree with the experimental data. Three types of metal-transfer modes (liquid bridge transition, droplet transition, and intermediate transition) are reproduced by simulations and confirmed by the experiments. The results show that as the heat input increases, the transfer mode changes from the droplet transfer mode to the liquid bridge mode. Therein, the liquid bridge transfer is the best for ensuring good print quality because of the stable metal-transfer behavior. More accurately, the liquid bridge is a dynamic equilibrium process. In the process, the metal transfer is mainly driven by the recoil pressure, while the surface tension always tends to break the bridge. The interaction between the two factors leads to the oscillation of the liquid bridge geometry morphology in the forming process, where the oscillation frequency is approximately 200 Hz. The droplet transition is observed when the dynamic equilibrium is broken. In this process, the Marangoni flow plays an important role in the droplet formation. Further, based on the transfer mode transformation mechanisms and a simple theory, a verified formula is proposed, according to which the energy required for maintaining the liquid bridge should be moderate. Therefore, the heat input conditions for maintaining the liquid bridge can be calculated quantitatively. This research is of considerable significance for understanding the physical processes in electron beam 3D printing and provides a promising avenue for process optimizations in industrial applications.

Buoyancy Induced Convection From Biheaters in a Cavity: A Numerical Study

A computational study of natural convection from biheaters of finite thickness and finite conductivity placed on a finite thickness and a finite conductive bottom plate of a cavity is performed under constant heat input condition. Cavity is cooled by the sidewalls, while the top and backside of the bottom plate are insulated. Streamline, isotherms, and local heat flux distribution of the sidewalls are discussed. Base Grashof number is chosen as 2.5 × 106. Biheater maintains a nondimensional distance of 0.4 between them. The left heater is placed at a nondimensional distance of 0.2 from the left wall. Heater length ratio is varied from 0.4 to 1.7, while heater strength ratio is varied from 0.25 to 7.0. Optimum operating temperature condition is found from the analysis.

Effect of Dynamic Reheating Controlled by the Weaving Width on the Microstructure of GTA Bead-On-Pipe Weld Metal of 25% Cr Super Duplex Stainless Steel

Gas tungsten arc welding (GTAW) with three different heat inputs controlled by the weaving width was performed to understand their effects on the microstructural changes during bead-on-pipe welding of super duplex stainless steel. The microstructure of the weld metals was categorized into three different types of zones: non-reheated, reheated type, and reheating-free zone. Even though single-pass welding with different weaving widths was employed, a reheated microstructure was detected, which has been previously observed with multiple pass welding. This phenomenon was called “dynamic reheating”, because it was produced by the weaving operation during welding regardless of the weaving width. The categorized area fraction varied with the weaving width change. Electron backscatter diffraction (EBSD) results at the edge (the area near the fusion line) of the low-heat-input condition indicated a higher austenite volume fraction and a lower Cr2N fraction than that of the medium heat input condition. Thus, it described an inverse relationship, because higher heat input provided a lower austenite fraction. In addition, it was observed clearly that the austenite fraction at the medium heat input condition was dramatically increased by reheating, while the Cr2N fraction was reduced. Regardless of the weaving width, reheating contributed to the increase of the austenite fraction, further reducing the Cr2N quantity. The edge areas in the map showed an inverse relationship in the reheated area fraction between low heat input and medium heat input. For this reason, the austenite fraction on the weld metal was determined not only by the heat input, but also by the amount of reheating.

Natural convection heat transfer characteristics of molten salt with internal heat generation

Molten salt is a promising heat transfer fluid with its high heat capacity, high boiling point, and chemical stability. In liquid fueled molten salt reactors and spent fuel reprocessing unit, molten salt carries heat generating fuel itself in a liquid state. To investigate the natural convection heat transfer performance of molten salt, a vertical heater vertical cooler rectangular loop filled with chloride salt containing liquid fuel, NaCl-KCl-(Pu, 238U)Cl3, is simulated using an open source CFD package, OpenFOAM under various heat input conditions; external heat flux, internal heat generation (IHG), and a combined heat input type condition. Different aspects of natural convection heat transfer according to heat input condition are found for same amount of total heat. The external heat flux condition generates a high temperature gradient near the heater wall with very thin thermal boundary layer due to the low thermal conductivity of molten salt. On the other hand, the IHG condition has a relatively flat temperature profile from its uniform volumetric heating. Due to the different behaviors of temperature evolution, local upward flow is formed only at the wall region under the heat flux condition, but global natural circulation flow is promoted under IHG condition. The combined type condition is largely dependent on how much heat exists in heat flux type, which strongly influences local heat and fluid phenomena in natural convection heat transfer. Molten salt has a high dependence on the heat input condition from its thermo-physical properties. Therefore, the distinct characteristics of molten salt and heat input conditions should be considered, when designing and analyzing the molten salt systems with both external and internal heating conditions.

Microstructure and corrosion behavior of S32101 stainless steel underwater dry and wet welded joints

This work focused on the microstructures, secondary phase precipitation and susceptibility to localized corrosion of UNS S32101 duplex stainless-steel welded joints that were welded using underwater dry and wet flux-cored arc welding (FCAW-136). The size and proportion of the austenite phases of the underwater dry welded joints were larger than those of the underwater wet welded joints under the same heat input conditions. In addition, the weld metal exhibited a better resistance to localized corrosion than the heat-affected zone. The high-temperature heat affected zones of the welded joints prepared using underwater dry welding showed improved performance compared with those prepared using underwater wet welding under the same heat input because of the reduced precipitation of chromium-rich nitrides. The resistance to localized corrosion of the low-temperature heat affected zone increased with increasing heat input for the underwater wet welded joints, whereas a reverse trend was observed for the low-temperature heat affected zone of the underwater dry welded joints.

Effects of Local Heat Input Conditions on the Thermophysical Properties of Super Duplex Stainless Steels (SDSS)

The properties of the super duplex stainless steels (SDSS) are strongly affected by the thermal history imposed by welding procedures. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this paper, we newly proposed a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure that combine the effects of temperature and phase changes during welding. We applied inverse method to fit the thermophysical parameters based on measured data. The model was verified by comparing measured and predicted temperature profiles using thermocouples located within the heat affected zone. Thus, an inverse method was implemented to obtain the parameters fitting for the grain growth evolution compatible with the final microstructure and grain size measured using SEM images and stereological techniques. We demonstrated that very small amount of non-equilibrium deleterious phases and nanosized precipitated are expected during the welding procedures depending upon the local conditions of temperature, compositions and alloying dilution evolutions.

Investigation of temperature dependent microstructure evolution of pure iron during friction stir welding using liquid CO2 rapid cooling

The microstructure evolution of pure iron during friction stir welding was reconstructed by an ingenious experimental design, in which the rapid cooling friction stir welding combined with the tool “stop action” technique and the subsequent short-time annealing were adopted to “freeze” the transient microstructure during the stirring and reproduce the normal cooling during conventional friction stir welding, respectively. The microstructure evolution during the stirring and normal cooling was investigated along the material flow path and in the annealed “frozen” weld zone by high-resolution electron-backscatter-diffraction technique. The results show that the continuous and discontinuous dynamic recrystallizations occur simultaneously at the severe deformation stage in front of the tool both under low and high heat input conditions. However, during the material flow, the microstructure evolution involves the plastic deformation, recrystallization, high angle boundaries migration and dynamic recovery under the low heat input condition, while in a dynamic balance of deformation, recrystallization and grain growth under the high heat input conditions. At the cooling stage, normal grain growth occurs both for the low and high heat input welding conditions, while it is very limited for the low heat input condition.

Relation between heat input condition and melting volume in Selective Laser Melting

Relation between heat input condition and melting volume in Selective Laser Melting

Effect of submerged arc welding process with one-side one-pass welding technique on distortion behavior of shipbuilding steel plate ASTM A131 grade A

Distortion induced by welding process is one of the major problems found in shipbuilding industries. Significant loss in time and cost to correct and repair this welding defect occurs whenever the distortion value exceeds the shipbuilding standard limitation. In addition, there is also a challenge to replace the common two-side welding with gouging technique currently used in Thai shipyards by the one-side one-pass welding technique to save time and cost during welding, flipping, and gouging steps. In this research, distortion and peak temperature during the one-side one-pass submerged arc welding of ASTM A131 Grade A steel plates were investigated by varying the effects of heat input levels (27 kJ/cm and 32 kJ/cm), joint design configurations (square butt joint and single 30° V-groove), and constraints (with and without fixtures). To prevent molten burn-through during welding with higher heat input, a ceramic backing was attached at the weld root. Based on the results, distortion varies with different joint types, heat input, and constraint conditions. The maximum distortion of 2.99 mm was found in the specimen welded with 32 kJ/cm and 30° V-groove without constraint. The proposed one-side one-pass welding technique using ceramic backing passes the distortion limitation enforced by the international shipbuilding standard, while improving the productivity for hull fabrication.

Effects of oxygen content on microstructure and impact toughness of high heat input flux-cored wire weld metals

Three weld metals with different oxygen contents were developed. The influence of oxygen contents on the microstructure and impact toughness of weld metal was investigated through high heat input welding tests. The results showed that a large number of fine inclusions were formed and distributed randomly in the weld metal with oxygen content of 500 ppm under the heat input condition of 341 kJ/cm. Substantial cross interlocked acicular ferritic grains were induced to generate in the vicinity of the inclusions, primarily leading to the high impact toughness at low temperature for the weld metal. With the increase of oxygen content, the number of fine inclusions distributed in the weld metal increased and the grain size of intragranular acicular ferrites decreased, which enhanced the impact toughness of the weld metal. Nevertheless, a further increase of oxygen content would contribute to a great diminution of the austenitic grain size. Following that the fraction of grain boundary and the start temperature of transformation increased, which facilitated the abundant formation of pro-eutectoid ferrites and resulted in a deteriorative impact toughness of the weld metal.

Semi-analytic solution of three-dimensional temperature distribution in multilayered materials based on explicit frequency response functions

Multilayer coatings have been widely using in a wide range of applications, including industrial, biological and electrical areas, and the thermal distribution in a multilayered material is of great interest. In present paper, the frequency response functions (FRFs) of temperature field under unit point heat flux are derived through thermal conduction equation. The unknown coefficients in the FRFs are assembled in a linear system of matrix equations according to the heat input and continuity condition of heat flux and temperature at each interface; then the coefficients are solved and expressed recursively. Based on the closed-form solution of FRFs, a fast semi-analytical method (SAM) is developed to solve the three-dimensional steady state heat conduction in arbitrary multilayered materials, and there are no limits on the number or the thickness of layers. The temperature fields under different kinds of heat flux in multilayered coatings are studied. Moving heat flux and convection on the surface are also considered.

Effects of Porosity, Heat Input and Post-Weld Heat Treatment on the Microstructure and Mechanical Properties of TIG Welded Joints of AA6082-T6

Various heat input conditions and post-weld heat treatments were adopted to investigate the microstructure evolution and mechanical properties of tungsten inert gas (TIG) welded joints of AA6082-T6 with porosity defects. The results show that the fracture location is uncertain when an as-welded joint has porosities in the weld zone (WZ), and overaging in the heat-affected zone (HAZ) at the same time. When the fracture of the as-welded joint occurs in the HAZ, the total heat input has a linear relation with the tensile strength of the joint. An excess heat input induces the overgrowth of Mg2Si precipitates in HAZ and the coarsening of α-Al grains in WZ, resulting in a decrease in the microhardness of the corresponding areas. After artificial aging treatment, the tensile strength of the welded joint is increased by approximately 9–13% as compared to that of as-welded joint, and fracture also occurs in HAZ. In contrast, for solution treated and artificial aging treated joint, fracture occurs suddenly at the rising phase of the tensile curve due to porosity defects throughout the weld metal. Furthermore, the eutectic Si particles of WZ coarsen and spheroidize after solution treatment and artificial aging treatment, due to the diffusion of Si to the surface of the original Si phases when soaking at high temperature.

Microstructure and mechanical properties of friction stir processed cast Eglin steel (ES-1)

Eglin steel, an ultra-high-strength steel developed for various demanding applications, is a low-cost alternative to 4340 steel, in which nickel and cobalt additions are replaced by higher tungsten additions, thereby achieving comparable strength and ductility. Friction stir processing (FSP) was carried out on this steel under two heat input conditions, which fell above the A3 transformation line. Microhardness values along the horizontal and vertical directions of the processed region cross section were reported for the lower heat input condition, and correlated with corresponding microstructures. A 3D heat transfer and material flow model was used to predict the peak temperature and cooling rates in these zones. Site-specific tensile tests of specimens extracted from the top to the bottom of the stir zone (SZ) showed ultimate tensile strength (UTS) greater than 2GPa, with a total elongation close to 10% at ~ 4mm from the top surface of SZ. Transmission electron microscopy (TEM) analysis of the high strength location showed microstructure consisting of nano-twinned martensite and nano-bainite laths of size ranging from 200nm to 300nm, and confirmed the existence of retained austenite. This mixed microstructure was comprised of finer aggregates of martensite, bainite and retained austenite, which were postulated to be responsible for the high strength and ductility combinations.

Steady state investigations of a commercial diffusion-absorption refrigerator: Experimental study and numerical simulations

Experimental investigations and numerical simulations of a low capacity commercial diffusion-absorption refrigerator (DAR) in stationary mode are carried out. The tests are performed under different heat input conditions. Optimal operation of the DAR refrigerator is reached with a power supply of 46 W at a generator temperature of 167 °C, corresponding to a coefficient of performance (COP) of 0.159. Numerical simulations of the refrigerator using a model developed with the commercial flow-sheeting Aspen-Plus software are also perfomed. The computer model is validated by comparing its predictions with experimental data for three generator heat supply rates: 46 W, 56 W and 67 W. Deviations between model predictions and experimental measurements in terms of cooling capacity and coefficient of performance are less than 1%. The proposed model could be very useful to predict the functioning of the commercial diffusion-absorption refrigerator under steady state regime.

Microstructure and properties of titanium alloy electron beam weldments based on the different heat input conditions of the same line energy

Electron beam welding (EBW) was applied to 20 mm thick marine high-strength titanium alloy Ti6321 with different heat input conditions of the same line energy, and microstructure, microhardness and tensile properties of the defect-free welded joints were examined. The results show that for small heat input (SHI) weld metal, martensite α′ phase was wide and intertwined and the residual β was relatively high. For large heat input (LHI), martensite α′ was relative small. Microstructure of the HAZ is inhomogeneous. For SHI, β phase collected in fusion line, and the heat affected zone of SHI had more residual β phase than that of LHI. XRD results indicate that the weld metal of LHI nearly consists of α′ martensitic phase but small quantity of β phase. However, the weld metal of SHI exists α′martensitic phase, β phase and some α phase. Microhardness values in the centre of weld metal of SHI decreases greatly because of α phase. While hardness of LHI weld metal is consistent. The fracture locations of LHI EBW joint specimens are in base metal, and the UTS of the joints reach 935 MPa. The fracture locations of SHI EBW joint specimens are in weld metal, and the UTS of the joints reach about 905 MPa.

Fracture Resistance of Flash Welded and Laser Welded Butt Joints in a Microalloyed HSLA Steel

High-strength, low-alloy (HSLA) steels are widely used in the automotive and oil industries due to their good mechanical properties and weldability. The selection of the welding process depends on several factors, including the quality of the weld bead and the production capacity. The knowledge of the mechanical performance of the welded joint is essential to ensure structural reliability. In the present work, butt joints were produced from 5 mm thick plates of a microalloyed HSLA steel by flash welding and by laser welding processes, the latter using two different heat input conditions. The microsctructure and hardness of the weld beads were evaluated. The fracture toughness of the welded joints was assessed by means of CTOD tests. The higher heat input laser welded joint presented critical CTOD comparable to that of the flash welded joint, whereas the lower heat input martensitic-bainitic laser welded joint tended to a brittle behavior.

Thermodynamic potential of Rankine and flash cycles for waste heat recovery in a heavy duty Diesel engine

In heavy duty Diesel engines more than 50% of the fuel energy is not converted to brake power, but is lost as heat. One promising way to recapture a portion of this heat and convert it to power is by using thermodynamic power cycles. Using the heavy duty Diesel engine as the waste heat source, this paper evaluates and compares the thermodynamic potential of different working fluids in four power cycles: the Rankine cycle (RC), the transcritical Rankine cycle (TRC), the trilateral flash cycle (TFC) and the single flash cycle (SFC). To establish the heat input into the cycle, operating conditions from an actual heavy duty Diesel engine are used as boundary conditions for the cycle heat source. A GT-Power model of the engine was previously developed and experimentally validated for the stationary points in the European Stationary Cycle (ESC). An energy analysis of this engine revealed that it has four heat sources with the potential for waste heat recovery: the charge air cooler (CAC), the coolant flow, the exhaust gas recirculation cooler (EGRC), and the exhaust flow. Using fixed heat input conditions determined by the selected engine operating mode, the TFC performed best for the CAC with a net power increase of around 2 kW, while the RC performed best for the coolant flow, with a net power increase of 5 kW. For the EGRC, ethanol performed especially well with both the RC and TRC, leading to an 8 kW net power increase. When using the exhaust as heat source, all four cycles provided a power output of around 5 kW with some variation depending on the working fluid. This study shows that for most cases, considering the different heat sources, the choice of cycle has a larger impact on the cycle performance than the choice of working fluid.