Optimum Heat Input Research Articles

Microstructure and Shape Memory Properties of Gas Tungsten Arc Welded Fe-17Mn-5Si-10Cr-4Ni-(V, C) Shape Memory Alloy.

In this study, microstructure, mechanical, and shape memory properties of the welded Fe-based shape memory alloy (Fe-SMA) plates with a nominal composition of Fe-17Mn-5Si-10Cr-4Ni-(V, C) (wt.%) by gas tungsten arc welding were investigated. The optimal heat input to ensure full penetration of the Fe-SMA plate with a thickness of 2 mm was found to be 0.12 kJ. The solidified grain morphology adjacent to the partially melted zone was columnar, whereas the equiaxed morphology emerged as solidification proceeded. The ultimate tensile decreased after welding owing to the much larger grain size of the fusion zone (FZ) and heat-affected zone (HAZ) than that of the base material (BM). Weldment showed lower pseudoelastic (PE) recovery strain and higher shape memory effect (SME) than those of the plate, which could be ascribed to the large grain size of the FZ and HAZ. Recovery stress (RS) slightly decreased after welding owing to lower mechanical properties of weldment. On the other hand, aging treatment significantly improved all PE recovery, SME, and RS via carbide precipitation. Digital image correlation analysis revealed that HAZ showed the lowest SME after heating and cooling, implying that the improved SME of FZ compensated for the low SME of the HAZ.

An Optimal Heat Input Control by Multi Heat Source in Laser Welding

An Optimal Heat Input Control by Multi Heat Source in Laser Welding

Crystallographic study on microstructure evolution and mechanical properties of coarse grained heat affected zone of a 500 MPa grade wind power steel

The effect of different welding heat inputs on the microstructure and mechanical properties of the simulated coarse grained heat affected zone (CGHAZ) of high-strength wind power steel with yield strength of 500 MPa has been investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Charpy impact tests have demonstrated that there exists an optimum heat input of ∼20 kJ/cm that allows optimum impact toughness to be obtained for the CGHAZ. It was shown that this is related to the refined bainitic structure and the highest density of high-angle grain boundaries (HAGBs) with misorientation angle of more than 45°. In crystallographic visualization studies, it was shown that the weakest variant selection occurs for the bainite transformation in the optimal heat input, leading to the highest density of HAGBs with each Closed-packet group containing two or three Bain groups and showing a staggered arrangement structure. The contribution that can effectively deflect and prevent crack propagation during impact experiments has to come from the block boundary. However, it was also found that the center segregation induced by C and Mn reduces the low-temperature impact toughness of the core sample before and after simulated welding, and affects the fluctuations of impact toughness and fatigue performance of simulated CGHAZ. Mn segregation can have a genetic effect on the welding heat affected zone, inducing a lower temperature martensitic transformation, which in turn leads to a decrease in low-temperature toughness and fatigue crack arrest performance.

Effect of Segregation Band on the Microstructure and Properties of a Wind Power Steel before and after Simulated Welding

This article uses scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD) to study the effect of C and Mn segregation on the microstructure and mechanical properties of high-strength steel with 20 mm thickness used for wind power before and after simulated welding. A Gleeble-3500 (GTC, Dynamic Systems Inc., Poestenkill, NY, USA) was used to study the microstructure evolution of the simulated coarse-grained heat-affected zone (CGHAZ) of experimental steel under different welding heat inputs (10, 14, 20, 30 and 50 kJ/cm) and its relationship with low-temperature impact toughness (−60 °C). The results indicate that alloy element segregation, especially Mn segregation, significantly affects the impact toughness scatter of the steel matrix, as it induces the formation of low-temperature martensite or hard phase, such as M/A (martensite/austenite) constituent. In addition, segregation also reduces the low-temperature impact toughness of the simulated welding samples and increases the fluctuation range. For high-strength steel with yield strength higher than 460 MPa used for wind power generation, there is an optimal welding heat input (~20 kJ/cm), which enables the simulated coarse-grained heat-affected zone (CGHAZ) to obtain the highest impact toughness due to the formation of lath bainite (LB) and the finest crystallographic block units. Excessive or insufficient heat input can induce the formation of coarse granular bainite (GB) or lath martensite (LM), leading to a larger size of crystallographic block units, reducing the hindering effect of brittle crack propagation and deteriorating low-temperature impact toughness.

Development of an experimental-analytical method for obtaining optimal two-layer welding window of a Ni–Cr–Mo–V alloy steel

This study investigates the feasibility of using two-layer tungsten inert gas (TIG) welding to repair damaged parts made of 3.5NiCrMoV low-alloy steel, which is widely used in various industries for complex and thick components. Experimental and analytical methods are used to determine the optimal heat input for the second layer of welding, which can eliminate the need for post weld heat treatment (PWHT). The first layer is welded with a heat input of 0.42 kJ/mm and the second layer is welded with heat inputs ranging from 0.59 to 0.92 kJ/mm. The effects of the second layer heat input on the microstructure, peak temperature profile, cooling rate, hardness, and impact energy of the welded alloy are evaluated. The optimal heat input for the second layer is found to be 0.76 kJ/mm, which is 1.8 times the heat input of the first layer. This heat input tempers the coarse-grained region in the heat affected zone (HAZ) caused by the first layer, maintains the hardness of the weld metal, and improves the impact energy of the welded alloy. This method is novel and useful because it can save time, money, and energy for repairing the damaged parts made of high strength low alloy steel. This method can also provide useful information for controlling the microstructure and mechanical properties of high strength low alloy steels during welding. Rosenthal's analytical models are used to simulate the temperature and cooling rate profiles of the welded metal and the HAZ, and the results are compared with the experimental data.

Advantages of Friction Welding of Fittings with Small Diameter Conical Contact Form

Introduction. As numerous production tests show, the use of manual arc welding (MAW) of thick-walled fittings of small diameter (up to 80 mm) does not provide a high-quality weld joint that meets the requirements of regulatory and technical documents of nuclear power plants (NPP). The solution to this problem is possible on the basis of research and development of welding technology with optimal heat input instead of MAW. Existing fusion welding technologies do not allow for optimal regulated heat input. However, this can be realized during the development and further use of the friction welding (FW) method. Therefore, this work aimed at developing a technology based on an automated technique of friction welding, which could provide the enhancing of the quality of weld joints of small diameter fittings of power equipment to the level of regulatory requirements.Materials and Methods. Small diameter fittings with a conical contact surface made of low-alloy steel 10GN2MFA were used. The experimental study was performed on a friction welding machine MST–41. Methods of non-destructive and destructive quality control were used in accordance with the regulatory and technical documentation of nuclear power engineering.Results. A methodology was developed, and the optimal dimensions of the conical contacting surface under welding were determined. It was shown that optimal heat input during friction welding was achieved by preparing a conical contacting surface in the angle range α = 30º–40º. The methodology and parameters of the friction welding mode for models of small diameter fittings were experimentally tested. In the course of the research, a cyclogram of the friction welding process was obtained and described, which confirmed the stage-by-stage formation of the weld joint due to the sequential inclusion of annular sections of the conical surface of the connected parts in the heating stage. The results of non-destructive and destructive testing were obtained, confirming the presence of a high-quality weld joint at the level of the requirements of the regulatory and technical documents of the NPP.Discussion and Conclusion. The obtained research results can be used to develop the technology of friction welding of pipes, as well as products made of carbon and low-alloy steels.

Predicting the thermal performance of screen mesh wick heat pipe with alumina nanofluids using response surface methodology

This study aims to investigate the effect of heat load, tilt angle, and volume concentration of alumina nanofluid on the thermal performance enhancement of cylindrical screen mesh wick heat pipe in terms of thermal resistance(R) and thermal conductivity(k). Response surface methodology based on the Box–Behnken design was implemented to investigate the influence of heat input (100–200 W), tilt angle (0–90°), and volume concentration (0.05–0.25 vol%) of nanofluid as the independent variables. Second-order polynomial equations were established to predict the responses, ‘R’, and ‘k’. The significance of the models was tested by means of analysis of variance (ANOVA). In addition, a correlation between the independent variables was derived in this study. The results revealed that the optimum heat input, inclination angle, and concentration of nanofluid were determined as 200 W, 52.72°, and 0.1773 vol. % respectively for both ‘R’ and ‘k’. SEM analysis was performed to observe the thermal performance phenomena of the heat pipe before and after experimentation.

Tensile and microstructural behavior of gas-tungsten-arc-welded electrolytic tough pitch copper joints

Electrolytic tough pitch (ETP) copper is extensively used in the manufacturing of electrical machines and automobiles. Compared with other pure coppers, ETP copper has lower weldability. Therefore, this study analyzes the weldability of ETP copper using the gas tungsten arc welding (GTAW) process. GTAW can be performed using constant-current (CC) and pulsed-current (PC) modes. Consequently, the properties of the joints fabricated using both modes are compared and analyzed in this study. The results show that the joint efficiencies of GTAW-CC and GTAW-PC joints are 81 and 89%, respectively. The optimal heat input and pulsating action in PC mode produce refined grains in the weld zone and heat-affected zone, resulting in a higher joint efficiency.

Influence of Heat Input on the Weldability of ASTM A131 DH36 Fillet Joints Welded by SMAW Underwater Wet Welding

Naval vessels face multiple risks that can damage their hulls during navigation, leading to on-site repairs through the shield metal arc welding (SMAW) process and underwater wet welding (UWW). This paper presents a weldability study to identify the optimal heat input parameters to improve ASTM A131 DH36 welded joints quality, development, and sustainability. This study analyzes the influence of heat input on the microstructure and mechanical properties of underwater wet welding fillet joints welded with shield metal arc welding at 4 m water depth in a real-life environment located at the bay of Cartagena (Colombia). The methodology involves nondestructive and destructive tests, including visual inspection, fillet weld break, scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers hardness, and shear strength tests. The welds microstructure is composed of ferrite, pearlite, retained austenite, bainite, and martensite; the hardness values range from 170 HV1 to 443 HV1, and the shear strength values range from 339 MPa to 504 MPa. This indicates that high thermal inputs improve the weld quality produced by the underwater wet welding technique and can comply with the technical acceptance criteria of AWS D3.6, making them more sustainable, with less welding resources wastage and less impact on marine ecosystems.

Comparative study of micro-sized Al particles enhancing the thermal joining of aluminum alloy-PA66 without or with reinforcement

The huge thermal difference between the aluminum alloy and polymer led to a low interface bonding strength, hindering the application of hybrid joints in the industries. Micro-sized aluminum (Al) particles were introduced into the polyamide 66 (PA66) resin substrates to improve the laser thermal joining of aluminum alloy to PA66 considering the heat conduction of metal particles. Results indicated the resin was physically reinforced after adding Al particles, enhancing the melting point and decomposition temperature due to the constraint on the polymer chain movement. The surface energy of PA66 resin was also increased because of the increase of polar functional groups, resulting in an enhancement of adhesion force between the aluminum alloy and resin. Furthermore, 3D thermally-conductive network formed between particles and resin substrates owing to the thermal vibration caused by Al electrons during the heat conduction, thereby strengthening the thermal conductivity of resin. This improved the thermal microscopic conductance at the interface, and the joining area at the interface dependent on the molten resin was thus enlarged. Finally, the tensile-shear force and strength of joints after adding Al particles were both significantly improved, reaching 1.35 times and 1.44 times of those without Al particles under the optimal heat input, respectively. This was achieved by a synergetic strengthening effect of enhanced adhesion force and joining area, providing a new method to obtain the high-quality joints.

Optimization of gas tungsten arc welding parameters for welding of super duplex stainless steel using factorial design

This study investigates the relationship between four welding input parameters (voltage, current, heat input, and welding speed) and the ultimate tensile strength (UTS) and yield strength (YS) of a welded joint. The work joined two super-duplex stainless-steel pipes of outside diameter 0.630 inches (16.002 mm) and a thickness of 0.065 (1.651 mm), using Gas Tungsten Arc Welding. Factorial design was used to ascertain the main and interaction effects of the welding input parameters on the UTS and YS of the welded joint. Results revealed a significant interaction between voltage, current, welding speed and heat input for UTS, and a significant interaction between the welding speed and heat input for YS. Results further revealed that as voltage increases from 9.3 V to 11.6 V, the UTS decreases by 2.69 MPa, while YS increases significantly by 24.25 MPa. When the current increases from 30 A to 38 A, the UTS increases by 10.81 MPa, while the YS increases by 4.25 MPa. In the case of the welding speed, an increase from 0.46 to 0.71 mm/s results in a decrease of the UTS by 7.94 MPa and a significant increase of the YS by 33.25 MPa. When the heat input increases from 0.54 to 0.70 kJ/mm, the UTS decreases by 15.06 MPa, whereas the YS decreases significantly by 35.25 MPa. Also, the optimum voltage, current, welding speed and heat input for UTS are 11.60 V, 30.0 A, 0.71 mm/s, and 0.70 kJ/mm, respectively, and those of YS are 9.30 V, 30.0 A, 0.46 mm/s, and 0.70 kJ/mm, respectively.

Microstructure, mechanical and electrochemical studies of dissimilar friction stir welded aluminium alloys

In the present investigation, the influence of tool rotational speed (900, 1100, 1300, and 1500 rpm) on microstructure, mechanical characteristics, and corrosion behavior of friction stir welding (FSW) of dissimilar Al5083–6061 alloys was studied. Optical and scanning electron microscopes were used to study the microstructural features. The grain size measured at the stir zone (SZ) decreased considerably in contrast with the base materials (BM) but increased with tool rotational speed. The mixing degrees of two materials at the SZ are enhanced by increasing rotational speeds. The mechanical properties, such as hardness and tensile properties, were studied using Vicker’s hardness tester and universal testing machine. The hardness of the weld joints is inferior to that of the base metal, and uniform hardness distribution and the highest average hardness in SZ were obtained at 1100 rpm. The higher strength and elongation of 202 MPa and 5.2%, respectively, were achieved at 1100 rpm, with joint efficiency of 65%, due to optimum heat input, and the lowest tensile strength and elongation of 156 MPa and 3.2%, respectively, were obtained at 1300 rpm with a joint efficiency of 50% due to excess heat input. It is curious to note that an increase in tensile elongation accompanies the enhancement of weld strength. The fracture occurred at the retreating side of the heat-affected zone as it is the weakest zone in the FSWed joint. Different corrosion tests, such as immersion, open circuit potential, and Tafel polarization tests, were carried out using an electrochemical workstation. The corrosion findings showed that the corrosion resistance of the samples increased after the welding, and the highest corrosion resistance was obtained at 1100 rpm.

Role of Carbon Content on Microstructure Evolution and Impact Toughness in Coarse-Grained Heat-Affected Zone of High-Strength Steel

The effect of carbon content in the base metals of high-strength steel on the microstructure and impact toughness of simulated welding focusing on a coarse-grained heat-affected zone (CGHAZ) at different heat inputs was systematically investigated by using scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD). The Charpy impact test confirmed that there was an optimal heat input, which caused the CGHAZ to obtain the highest impact toughness. The optimal heat input is ~20 kJ/cm and remains unchanged with an increase in carbon content from 0.04 to 0.12 wt.%. However, the impact toughness of the CGHAZ decreases with the increase in carbon content at each heat input. Microstructure characterization showed that a CGHAZ with 0.04 wt.% carbon gradually changed from lath bainite (LB) to granular bainite (GB) with an increase in heat input, while it changed from lath martensite (LM) to LB and then to GB for a CGHAZ with 0.12 wt.% carbon. Although the density of high-angle grain boundaries (HAGBs) obtained at 20 kJ/cm in the high-carbon sample is higher than that of the low-carbon sample, its impact toughness is lower, which is related to the parallel structure of the lath bundles and the morphology the austenite penetration.

Enhancement of tribological and mechanical properties of TiB2 - Co cladded layer developed by tungsten inert gas cladding on AISI 1020 Steel

In the present study, various compositions of TiB2-Co coating were deposited on AISI 1020 mild steel by tungsten inert gas cladding method. In this work, various heat energy of TIG with a fixed travelling speed of 1.5 mm s−1 was used to deposit the coating layer. The aim of this study was to investigate the optimal heat input of TIG to develop a thick layer in terms of coating microstructure and bonding quality. The influence of cobalt addition and current variation on microhardness and wear properties of the cladded layer was also investigated. The metallographic examination and microstructural analysis were investigated by x-ray diffraction, scanning electron microscope (SEM) and energy dispersive spectroscopy. The microhardness and wear rate have been analyzed by Vickers microhardness and dry sliding wear test, respectively. The investigations reveal that the influence of heat input on the wear resistance and hardness of the coated layer was significant. The microhardness value increases with increase in wt.% of TiB2 coating powder when TIG parameter is constant. The microhardness value also increases with decrease in heat input of the TIG when composition of the coating is kept constant. The maximum microhardness value was achieved up to 2563 HV0.1 which was 15 times higher than the substrate hardness value of 170 HV0.1. From the wear test result, it was noticed that the minimum wear rate found was 8.24 × 10–8 g Nm−1 for the coating composed by lower heat input (720 J mm−1) and higher wt.% of TiB2 (90 wt.%).

Optimization and prediction of heat input of mild steel weldment, using genetic algorithm

In welding materials, the purpose is to resist the variation of the microstructure of the material and retain the mechanical properties and the chemical properties. Most welded joint fail due to the utilization of poor welding process. This poor welding process produces a minimum heat input that could cause insufficient melting of the electrode, insufficient melting of the electrode is responsible for inadequate penetration of liquid metal into the welded joint. Literature has shown that produced welded joints by insufficient penetration of the liquid metal have low bearing capacity. This indicates that such welded joints would not be able to sustain the design load. In order to achieve deep liquid metal penetration, optimizing and prediction of heat input of mild steel weldment, utilizing genetic algorithm is studied. The purpose of this study therefore is to develop models that would minimize the heat input. Genetic Algorithm which imitates the evolution progression and functions on the principle of the natural theory choice with evolution was utilized for the result analysis. It was shown as a result that combination of welding time 79.15 sec current of 239.03 A welding speed of 56.59 mm/s voltage of 29.87 v feed rate of 130 mm/s will produce optimal heat input of 117.30 KJ

Effect of Dwell Time on Fracture Load of Friction Stir Spot Welded Dissimilar Metal Joints

The dissimilar materials joining in heavy structural fabrication industries is tedious work for welding and design engineers, since the weld region’s criticality is encountered by hot cracking and its associated problems. Moreover, dissimilar materials are joined by mechanical locking such as rivets, bolt and nuts, and screws. Nowadays, the fasteners are eliminated by friction stir welding (FSW). The friction stir spot welding (FSSW) is a variant of FSW; it can be avoided by seam welding. Hence, in this investigation, FSSW is used for joining AA6061 aluminum alloy with mild steel using tool rotation speed, plunge depth and rate, and shoulder to pin diameter ratio. The experimental method observed that the joint fabricated with a rotational speed of 1000 rpm, plunge rate of 5 mm/min, plunge depth of 6 mm/min, and shoulder diameter to pin diameter ration of 3.0 yielded highest fracture load The optimum heat input could obtain the improvement in FSSW joint strength. Recrystallized grains and favorable intermetallic compound formation are the primary factors for sound welding.

Welding heat input for synergistic improvement in toughness and stress corrosion resistance of X65 pipeline steel with pre-strain

The microstructure, hydrogen embrittlement sensitivity, fracture toughness, and influence of pre-strain on the sulfide stress corrosion cracking (SSCC) sensitivity of the coarse-grained heat-affected zone of X65 pipeline steel with large deformation were studied to determine the optimal welding heat input in an acidic H2S environment. After pre-straining, the microstructures of the specimens changed insignificantly, but their ductility decreased. The acicular ferrite microstructure obtained under a low heat input demonstrated the synergistic improvement in the SSCC resistance and fracture toughness under pre-strain, especially at t8/5 = 20 s. The M/A constituents interface potentially causes microcrack initiation and interconnection under pre-strain.

Microstructural and mechanical analysis of double pass dissimilar welds of twinning induced plasticity steel to austenitic/duplex stainless steels

Double pass dissimilar welds between the twinning induced plasticity (TWIP) steel and austenitic stainless steel (ASS) AISI 304 L and duplex stainless steel (DSS) 2205 were studied theoretically and experimentally. A finite element (FE) thermal model linked to the liquid fraction calculation was used to estimate the optimal heat input level. The metallographic characterization of dissimilar weldments TWIP-SS 304 L and TWIP-DSS 2205 disclosed a priori the lack of hot cracking in the fusion zone (FZ) and liquation cracks in the heat-affected zone (HAZ). Later, the root bend test results corroborated a lack of fusion in the FZ-HAZ interface of the TWIP-DSS 2205 weld (TWIP steel side). The FE model predicted the heat accumulation in the SS 304 L and DSS 2205, which produced variation in the thermal gradient. The thermal gradient changes induced the ferritic-austenitic (FA) solidification mode in TWIP steel and SS 304 L and the massive austenite formation by epitaxial growth in the FZ-HAZ interface of the DSS 2205 side. Microhardness profiles corroborated the formation of homogenous FZs in both dissimilar welded joints. The microhardness increase/decrease was related to the solidification mode change in the FZ-HAZ interface. The mechanical strength and ductility of the TWIP-SS 304 L weld decreased 26% and 40%, respectively, compared to the reference autogenous similar weldment SS 304 L. The planar solidification growth detected in the FZ-HAZ interface was responsible for mechanical properties loss.

Investigating the effect of GTAW parameters on the porosity formation of C70600 copper-nickel alloy

ABSTRACT In this study, the optimisation of welding parameters was investigated in a cupronickel alloy. The welding process was gas tungsten arc welding (GTAW) which is a prevalent method for welding pipes. The filler material type, shielding gas, and welding conditions were considered constant parameters, while heat input, shielding gas flow rate, wind flow speed and arc length were the variable parameters. In order to control variables precisely, the test coupons were assembled on a hand-made rotating machine with a controlled rotational speed. The microstructure and mechanical properties of the welded specimens were examined through the metallography and tensile test, respectively. The results showed that the optimum heat input and flow rate, which resulted in the lowest amount of porosity, were 10.2–11.3 kJ/cm and 6 L/min, respectively. It was also shown that by increasing the wind flow speed from 3 to 10 km/h, the porosity increased from 1.4% to 14.8%. In addition, reducing the arc length from 2 to 1 mm led to better weld protection and arc stability and consequently resulted in decreasing the amount of porosity from 1.1% to 0.23%. The tensile test results showed that the ultimate tensile strength of the welded specimen using appropriate parameters will be significantly reduced if improper welding parameters are used. The main reason for this decrease was the increase of porosity.

An investigation on laser/DP-MIG hybrid weldability of aluminum to Al-Si coated boron steel

Laser/double pulse-MIG (laser/DP-MIG) hybrid welding-brazing of 5052 aluminum alloy to Al-Si coated boron steel was successfully conducted in a lap configuration with an Al-5Si filler. The heat input plays a significant role in determining the welding performance. The satisfactory appearance and excellent brazed interface with a maximum thickness of 4.1 μm was achieved at the optimum heat input of 161.8 J/mm, and the maximum joint strength reached to 168.8 MPa in excess of 75% aluminum resistance. Three kinds of intermetallic compounds (IMC) phases were nicely identified: τ5-Fe2Al8Si, θ-Fe(Al,Si)3 and η-Fe2(Al,Si)5. Microstructure evolution of brazed joint showed that microstructure of upper-critical HAZ (UCHAZ) consisted of martensite whereas that of inter-critical HAZ (ICHAZ) consisted of ferrite and martensite. The two failure modes (interfacial failure (IF) and HAZ failure (HF)) was associated with the interfacial characteristic and porosity percentage. IF mode was a typical intergranular fracture, and its cracks initiated from notch of weld joint and then redirected toward the region of pore concentration. HF mode was a mixture of major ductile fracture and minor cleavage fracture, and its cracks might initiate from notch of weld joint and then propagated along the IMC throughout the whole interface.