Welding Heat Input Research Articles

Microstructure evolution and mechanical properties of laser-welded joints of 1.2 GPa-class quenching and partitioning steel

Laser welding of 1.2 GPa-class cold-rolled quenching and partitioning steel with martensite + retained austenite microstructure was performed at different heat inputs ranging from 91–240 J·mm−1 using a CO2 laser. Scanning electron microscopy, electron backscatter diffraction, and uniaxial tensile testing equipped with digital image correlation were employed to characterize the microstructural and mechanical evolution of the joints. The results revealed that the fusion zone and upper-critical HAZ comprised full martensite with high microhardness. The HAZ contained a narrow softened zone with a minimum width of ∼0.6 µm and at least 48 HV microhardness drop because of the martensite tempering. Martensite decomposition and precipitation of carbides were noticeable at higher heat inputs, so that the hardness of the softened zone was declined. At the welding heat input of 91 J·mm−1, the yield and tensile strengths were 841 and 1270 MPa, respectively, which represented reductions of 5.5 and 0.78% compared to the base material properties. The joint efficiency of 99.2% was achieved at the lowest heat input. The tensile deformation was primarily concentrated in the softened zone and was small in the fusion zone. However, the participation of the base material to tensile deformation was enhanced at lower heat inputs, leading to higher elongation values up to ∼11.9% during tensile testing.

Bending deformation control in a laser-welded long straight structure by elastic pre-bending technique

Longitudinal bending deformation is the most typical mode of welding deformation in long-straight welded structures with asymmetric cross-sections. It is very critical for manufacturing accuracy to control the longitudinal bending deformation during the welding assembly stage. The objective of this study is to propose an elastic pre-bending technique to control the longitudinal bending deformation induced by welding heat input. Both numerical simulation technology and experimental method are employed to investigate the longitudinal bending deformation in a large-straight structure made of SUS304 stainless steel. In the current study, the effectiveness of the proposed elastic pre-bending method is verified by experiment. Simulation results show that the longitudinal bending deformation caused by welding could be reduced by >90 % by setting an appropriate value of pre-bending deformation. In addition, based on theoretical analysis and simulation results, the control mechanism of longitudinal bending deformation is clarified.

A Study on Gap Bridging Formation Conditions in Butt Root Pass Welding Using GTAW

GTA welding is a representative welding technique applied to root pass welding of piping. The pipe root pass welding significantly influences the determination of welding parameters owing to the root gap and step change occurring during installation. GTA welding has the advantage of being able to control current (A) and wire feeding speed (WFS) as independent variables; however, determining these variables is difficult. In this study, the change in the back bead height (Bbh) was observed by changing the root gap and WFS while the welding speed and welding current (A) were fixed. By fixing the welding speed and changing the welding current (A), root gap, and WFS, the gap bridging possible condition was expressed as a region. When the root gap changed from 0~1 mm and from 1~2 mm, the back bead height was greater than or equal to 0 mm. Possible welding current and WFS and the setting range of the welding heat input ratio (HIR) were presented.

Numerical modelling on the influence of repair welding during manufacturing on residual stresses and distortions of T-joints

Related to weld quality, level of imperfections is limited which can result in the need of grinding and repair welding. It results in material removal and additional heat cycles causing superimposed distortions and altering the distribution of residual stresses. The current paper investigates the influence of repair welding using welding simulation. Small-scale T-joint is analysed and used for validating the numerical model based on macrographs and distortion measurements. Furthermore, a parametric numerical analysis is conducted to evaluate the influence of repair welding sequence, heat input, and weld size. The research highlights the significance of welding technology and the importance of avoiding repair welding. Plastic strain increment of approx. 33 % occurred in the analysed T-joint, while von Mises residual stress peak increased approx. 26 % at the weld toe due to rewelding. Rewelding sequence had the most significant impact on final distortions; angular distortions could be tripled or nearly zeroed out. On the other hand, a quasi-linear relationship was evaluated between maximum transverse distortion and rewelding heat input. In addition, maximum von Mises stress peak was approximately 500 MPa on the rewelded side, regardless of the fillet size.

Influence of heat input on temperature and stress field of X80 steel pipeline cirumferential weld using type-B sleeve repairing

Abstract The multi-pass fillet welds of casing pipe were welded onto the in-service pipeline, which is widely used in pipeline repairs. However, the influence of welding heat input of B-type sleeve circumferential fillet weld on the temperature and stress field at the pipe circumferential weld is still unclear. In this paper, a double ellipsoid heat source model is developed to investigate the weld temperature field, residual stress field, and deformation field of the repair welding in service. The results show that the increase of weld heat input can effectively increase the size of the weld pool and the size of the high-temperature zone of the B-type sleeve circumferential fillet weld. And the peak temperature of the inner wall of the pipe girth weld increases with the increase of welding heat input of the sleeve circumferential fillet weld. The axial stress peak of the inner wall of the pipe girth weld reduces with the increase of welding heat input of sleeve circumferential fillet weld, and the axial deformation peak of the inner wall of the pipe girth weld increases first and then decreases with the increase of welding heat input of sleeve circumferential fillet weld.

The impact of welding heat input on microstructure, micro-texture, and mechanical properties of stir zone in friction stir welded DP600 steel

In this research, the impact of the heat input (HI) used during friction stir welding (FSW) on the microstructure, micro-texture and mechanical properties of DP600 steel was examined. Two different sets of rotational and transverse speeds were utilized to produce robust welds, one with low HI and the other with high. The outcomes demonstrated that various products such as polygonal ferrite (PF), Widmanstatten ferrite (WF), ferrite-carbide aggregate (FCA), and bainite were created in the stir zone (SZ) during the FSW of DP600 steel. After microscopic analysis, it was found that the high HI weld exhibited a greater amount of WF and bainite, resulting in higher hardness and ultimate tensile strength values than the low HI weld. The low HI weld displayed texture components including D1, D2, and E, with a slight cube component. These components were thought to result from the transformation of a strong B texture component and a weaker R texture component of prior austenite, indicating continious dynamic recrystallization during the FSW process. On the other hand, the high HI sample had a strong cube texture component and a weaker D shear component, a result of the transformation of a strong R shear texture component of prior austenite, suggesting discountinious dynamic recrystallization during FSW. The study determined that the welding HI greatly influences the proportion of microconstituents, the development of micro-texture, and the mechanical characteristics of the SZ during the FSW of DP600 steel.

Influence of Ti/N Ratio on Inclusions, Microstructures, and Toughness in Heat‐Affected Zone of Shipbuilding Steel Plates with Mg Deoxidation after High Heat Input Welding

The inclusions, microstructures, and toughness in heat‐affected zone (HAZ) of the shipbuilding steel plates with Mg deoxidation and the different Ti/N ratios are studied after the high heat input welding of 400 kJ cm−1. With increasing the Ti/N ratio from 3.00 to 5.67, the average size of inclusions increases, the mass fraction of total TiC inclusions increase from 2.8% to 5.0%, and the average size of MgO–TiN–MnS increases from 2.82 to 5.49 μm, while the number density that can induce intragranular acicular ferrite (IAF) nucleation decreases from 87 to 62 mm−2. These changes in inclusions are detrimental to induce the IAF nucleation. The HAZ microstructures are composed of the IAFs, polygonal ferrites, and upper bainites (UBs). With increasing the Ti/N ratio, the area fraction of the IAFs decreases from 44% to 14%, and the area fraction of UBs increases from 1.8% to 9.5%. The HAZ fracture mode changes from ductile fracture to brittle fracture after the high heat input welding of 400 kJ cm−1, and the HAZ toughness decreases from 183.3 to 48.7 J at −20 °C.

In-service welding of X70 steel gas pipeline: Numerical and experimental investigations

The in-service welding process is widely used to repair defective gas pipelines, which allows the damaged section to be repaired without interrupting gas flow. In this way, consumers and gas transportation companies will be able to minimize losses. In this study, a thermomechanical finite element analysis model was developed to examine the effects of pipe pressure, thickness, diameters, and welding heat input on temperature history and residual stress. The results were analyzed using the design of the experiment method (DOE). According to the results, these parameters significantly affect the thermal distribution and pipe yield stress at the welding point by 48.8%, 29.4%, 15.1 and 6.9%, respectively. On the basis of optimal conditions, in-service welding is conducted. Investigations were conducted on the microstructure, temperature distribution, and residual stresses induced during the in-service welding of API 5L X70 steel pipelines. As a result, it was determined that the HAZ microstructure consists primarily of ferrite, bainite, and M/A constituents, whereas the pipe microstructure undergoes fewer phase transformations. In order to validate the numerical model, mechanical tests, as well as hole drilling, were conducted to gather data, and a combination of equivalent carbon and T8/5 was used to determine hardness at various locations in the HAZ in order to determine which areas are susceptible to cold cracking. The numerical results and the experimental results were highly concordant.

Toughening Mechanism of Large Heat Input Weld Metal for Marine Engineering Extra-Thick Plate

Toughening Mechanism of Large Heat Input Weld Metal for Marine Engineering Extra-Thick Plate

Investigation of Hardfacing on Ultra-High Strength Steel Base Material

The application of high-strength steels is increasing rapidly nowadays, and steels with more than 1000 MPa yield strength are usually used in welded structures. The welding of these materials has many difficulties, so very important the precise technology planning, and disciplined work during welding. The weldability of these materials is commonly investigated field in case of joining. The application of ultra-high strength steels expands rapidly, and in the last years, it started to use them as a base material for hardfacing. Besides the wearing, there is a claim about higher strength of base materials in case of relatively extremely loaded machines. Because this ultra-high strength steel appears as a base material for hardfacing and it brings new challenges for welding technologists. In case of joining, the welding technology is complicated, usually need preheating before welding, is important to calculate and to use the right t8/5 cooling time, and basically necessary to decrease the heat input as much as possible. The bad effect of welding heat input can be compensated by the filler material too in some cases. In contrast in case of hardfacing the base material itself usually has a big thickness, and no joint preparation, additionally important to reach deep fusion on the surface. It basically determines the heat input which has a different heat cycle as in case of joining. Therefore, the heat affected zone (HAZ) differs from the HAZ in case of joining application. In this investigation, four different hardfacing were made with four different technological parameters by robotic gas metal arc welding on S1100QL steel. During the welding parameter determination, we try to find a series of heat inputs from the lowest to the practically usable highest heat input. For the experiments, two filler materials used, one for the buffer zone, and for the hardfacing itself. Microstructural evaluation and hardness tests were made on the specimens which can show the differences between the heat affected zones.

Application of Static Magnetic Field to Modify Heat and Mass Transfer during Welding of Shipbuilding Steel

Welding process is very important in numerous industries ranging from automotive and aviation to shipbuilding and pressure vessel production. Nowadays new methods to improve the productivity and quality of various welding techniques are searched. In many industrial applications even small process optimizations may lead to significant cost and energy savings and new applications. Large plate welding is particularly important in shipbuilding industry. It is common to weld multiple times to join thick plates, but this approach is not optimal from energy and time effectiveness and outcome quality is limited. Alternative is single high heat input welding, which causes various problems related to rapid local overheating and the formation of inhomogeneous post-weld microstructure. There are several heat affected zones near the weld pool, which has different properties and microstructure due to different cooling rates and heat flux orientation during solidification. Since welding is a complex multiphysical process there are various parameters such as electric current, oxygen presence, heat flow and weld pool flow which influence the quality of welding joint and efficiency of the process. In this paper we aim to experimentally and theoretically investigate how to modify heat and mass transfer in the weld pool and heat affected zone by static magnetic fields. Electromagnetic force is one of the ways how to affect the weld pool flow and to influence the heat and mass transfer from the weld pool to the base metal. Our research demonstrates that moderate DC magnetic field can cause various effects on the post-weld morphology, depending on the magnetic field direction. Analytical estimates and similarity analysis for high heat input welding on EH36 shipbuilding steel shows that electromagnetic methods, like application of DC magnetic field can be promising approach for improved welding outcome in some cases.

Electrochemical aspects and in vitro biocompatibility of Ti-SS304 layered composite

In the current research, in order to eliminate the release of toxic ions from the stainless steel 304 layer, a bi-layered Ti-SS304 biocomposite was made using the friction stir welding process, and the corrosion-cellular behavior of this biocomposite in simulated body fluid (SBF) was studied. The results show that the increasing temperature induced by increasing welding heat input during friction stir welding increases the thickness of the oxide layer formed on the titanium layer. By increasing the thickness of the oxide layer, the corrosion current density increases to 3.45 μA cm−2, the corrosion potential decreases to −0.24 V, and the corrosion rate increases to 0.029 mm/year. In addition, compared to samples fabricated with different traverse speeds of 5, 10, and 20 mm/min, the composite samples fabricated with different rotational speeds of 600, 800, and 1000 rpm did not show significant differences in corrosion current density due to competition effect of the titanium oxide layer and residual stress formed during friction stir welding by different rotational speeds. The two-layered Ti-SS304 composite fabricated at a rotation speed of 1000 rpm and a traverse speed of 20 mm/min shows the lowest corrosion current density and corrosion rate and the highest cell viability of 4.9 × 10 −7 A/cm−2, 4.26 × 10 −3 mm/year, and 92%, respectively.

Effects of Ti/N Ratio on Coarse-Grain Heat-Affected Zone Microstructure Evolution and Low-Temperature Impact Toughness of High Heat Input Welding Steel

Coarse-grain heat-affected zone (CGHAZ) properties of steel deteriorate when it is welded using high heat input, which always restricts the promotion and use of high heat input welding steel. TiN particles significantly inhibit the growth of austenite and improve the microstructure and properties of high heat input welding steel. Effects of different Ti/N ratios on the CGHAZ microstructure and properties of high heat input welding steel were studied using welding thermal simulations and in situ observations. Results showed that a higher Ti/N ratio led to the abnormal growth of austenite grains and promoted the nucleation and growth of lath ferrite, which made the microstructure of the CGHAZ heterogeneous. In contrast, austenite grains were more uniform at a lower Ti/N ratio. Thus, the microstructure was refined, the brittle structure was reduced, and the properties of the CGHAZ were improved. In addition, when Ti/N = 5.85, the impact absorption energy of the CGHAZ obviously fluctuated. However, when Ti/N = 2.82, the impact absorption energy of the CGHAZ was higher and more stable. These results provided a new idea for the development of high heat input welding steel based on TiN theory.

A Predictive Model for Weld Properties in AA-7075-FSW: A Heterogeneous AMIS-Ensemble Machine Learning Approach

This study addresses the research gap in materials science by developing an integrated predictive model for Ultimate Tensile Strength (UTS), Maximum Hardness (MH), and Heat Input (HI) in AA-7075 Friction Stir Welding (FSW). The aim is to enhance welding procedures, particularly in high-precision industries like aerospace and automotive. By incorporating four control parameters (Tilt Angle, Rotation Speed, Welding Speed, and Shoulder Diameter) and utilizing a Long Short-Term Memory (LSTM) machine learning model, a Heterogeneous Ensemble Machine Learning (He-EM) approach is developed. The Artificial Multiple Intelligence System (AMIS) optimizes the decision fusion strategy of each technique, ensuring the model's effectiveness. Validated using diverse experimental design methods and three datasets, the proposed AMIS He-EM model outperforms existing techniques (GPR, SVM, HE-UWE, and HE-WEDE) by significant margins (35.12%, 24.92%, 22.31%, and 15.48% respectively). The model's robustness is demonstrated, as its performance remains consistent across different experimental design methods. The key finding of this research is the remarkable improvement in accuracy for predicting UTS, MH, and HI in AA7075 FSW. This study highlights the importance of incorporating four control parameters and utilizing the D-optimal design for efficient exploration of the input parameter space. The implications of this research are profound, offering opportunities to optimize welding procedures, improve product performance, and streamline manufacturing processes in industries relying on AA7075 FSW.

Study on the Morphology, Microstructure, and Properties of 6082-T6 Aluminum Alloy Joints in MIG Welding

In this paper, metal inert gas (MIG) welding of 6082-T6 aluminum alloy with a thickness of 4 mm was simulated using a double ellipsoidal heat source. Based on the simulation results, the evolution of the microstructure, the strengthening mechanism of mechanical properties, and the corrosion characteristics of the welded joint were studied further. The thermal cycle curve of the welded joint was obtained through numerical simulation. When the heat input was 2.34–2.75 KJ/mm, the temperature of the welded joint reached the melting point of the material. With the increase in welding heat input, the weld metal (WM) organization changed from the dendrite to the cellular crystal transformation and presented a uniform distribution. The precipitation of the strengthened phase was inhibited at 2.75 KJ/mm. When the heat input changed from small to large, the tensile strength and toughness first increased and then weakened. Dimple distribution of tensile fractures was observed with a scanning electron microscope. When the welding heat input was 2.57 KJ/mm, the mechanical properties of the joint were the best. The tensile strength can reach 76.62% of the base material, and the elongation after breaking can reach 59.38% of the base material. However, it was concluded through studying electrochemical corrosion that the corrosion resistance of welded joints under this parameter was the worst. This may be caused by the presence of Cu, Fe, Si, Mg, and other compounds, and was proven to be Mg2Si through EDS analysis.

Weld formation, microstructure and mechanical properties of magnesium alloy and Al-Si-coated steel dissimilar lap joints fabricated by the CMT weld-brazing process

Magnesium alloy and Al-Si-coated steel dissimilar lap joints were joined using the CMT welding process. The weld formation, microstructure and mechanical properties of Mg/steel CMT weld-brazing joints were investigated. The wetting and spreading behaviour of the molten magnesium alloy filler material on the steel substrate were evidently improved owing to the presence of the Al-Si coating. The Fe-Al intermetallic reaction layer formed at the interface and enhanced metallurgical bonding between the magnesium alloy and steel. The effects of the Al-Si coating and welding heat input on interface layer characteristics were particularly assessed. When the heat input was 178.1 J/mm, the tensile shear strength of the Mg/steel welded joints reached 359.3 N/mm. The fracture modes and failure mechanism for tensile shear specimens were analysed and discussed in detail.

Influence of Different Weld Heat Input on Microstructure and Properties of New Martensitic Heat-resistant Steel Joints by Automatic Welding

In this article, the influence of different automatic weld heat input about the microstructure and properties of the joint of new martensitic heat resistant steel of P92 is studied. Based on this, the key factors to obtain excellent quality of P92 joint are proposed. The results show that the weld is tempered martensite microstructure, the grain of Heat-affected zone (HAZ) is finer with the weld heat input lower. The width of the slats and the crystalline size of the coarse-grained zone (CGHAZ) in the weld metal microstructure is gradually larger with the heat input higher. Meanwhile, as the welding heat input increase, the hardness of weld bead in the welded joint of P92 steel has a gradual downward trend, the impact toughness has a significant decrease, and the impact fracture morphology changes from ductile fracture to brittle fracture. Therefore, when the automatic welding technology is used to repair P92, so as to obtain better performance of welded joints, appropriate gas protection flow and welding parameters should be ensured according to welding thickness, and heat input should be strictly controlled.

Residual stresses in austenitic thin-walled pipe girth welds: Manufacture and measurements

Determining residual stresses in thin-walled pipes is challenging. They are potentially difficult targets for simulation, because they may not behave as simple axisymmetric structures during welding. Thin-walled pipes are more sensitive to changes in the welding heat input than thick-walled pipes. They are also under-represented in the existing population of residual stress measurements used to generate upper bound residual stress profiles for structural integrity assessments. In this paper, residual stress characterisation of two thin-walled austenitic girth welded pipes is presented. The overall geometries of the two mock-up designs were the same; they differed in the linear heat input per pass and the total number of weld passes. The residual stress characterisation was carried out using two independent measurement techniques; the contour method and neutron diffraction. The multiple-cut contour strategy was implemented to measure the cross-sectional maps of hoop and axial stresses on axial-radial and hoop-radial planes respectively. The contour method results are compared with stresses measured using neutron diffraction and specific residual stress distribution signatures observed are discussed.

Elucidating the heat input on CGHAZ microstructure and its irregular effect on impact toughness for a novel V–N microalloying weathering steel

This study investigated the effect of heat inputs on coarse-grained heat affected zone (CGHAZ) microstructure and impact properties of a novel vanadium (V) and nitrogen (N) microalloyed weathering steel via a Gleeble™ system, revealing the metallurgical essence of the steel suitable for large heat input (Ej) welding. The results indicate that in CGHAZ, the dominant microstructure was composed of lath bainitic ferrite (LBF) at Ej = 15 kJ/cm, granular bainitic ferrite (GBF) at Ej = 35 kJ/cm, and a mixture of intragranular acicular ferrite (IGAF), intragranular polygon ferrite (IGPF) and grain boundary polygonal ferrite (GBPF) at Ej = 55 and 75 kJ/cm, respectively, apart from martensite/austenite (M/A) constituents in each one. The area fraction, fM/A, and mean size, dM/A, of M/A constituents increased monotonously with the Ej. In addition, with increasing Ej from 15 to 35 kJ/cm, the fraction, fMTAs＞15°, of high-angle grain boundaries (HAGBs) with misorientation tolerance angles (MTAs) greater than 15° reduced, while the mean equivalent diameter, MEDMTA≥15°, of grains with HAGBs increased. However, as Ej further increased to 55 and 75 kJ/cm as the two large heat inputs, the precipitation of (Ti, V) (C, N) and thereby the heterogeneous nucleation of polygonal and acicular ferrite were promoted by a lowered degree of undercooling, resulting in the decreased MEDMTA≥15° and the increased fraction fMTAs＞15°. Accordingly, the impact toughness of CGHAZ was degraded with the increase of Ej from 15 to 35 kJ/cm, but enhanced with the increase of Ej from 35 to 75 kJ/cm.

Fatigue crack growth behavior for gas tungsten arc welded joint of TC2 titanium alloys sheets

Gas tungsten arc welding (GTAW) is a most preferred welding method for titanium alloys. Due to severe inhomogeneity of welded joints resulting from welding heat input and stress concentration, the joints are prone to fatigue crack initiation, and the fatigue crack growth rate (FCGR) and direction have great variability. Thus, it is of great significance to master the fatigue crack growth (FCG) behavior for the evaluation of remaining life. The FCGR tests were performed in different zones of the TC2 titanium alloy joints welded by the GTAW, and the acceleration behavior of the FCG was investigated. The results show that the crack growth is accelerated prematurely at stable crack growth stage (stage II). The precracks in the weld zone (WZ) and heat affected zone (HAZ) present cross-regional growth during the acceleration process. The regions before and after the critical acceleration point correspond to stage IIa and stage IIb, respectively. The FCG life at the stage IIa accounts for 90% of the total life, and the stress intensity factor range at the critical acceleration point is much lower than that at the instability point. It is proposed that the critical acceleration point is taken as the remaining life evaluation point of the TC2 titanium alloy gas tungsten arc welded joint, and the crack should be limited to the stage IIa, where the FCGR decreases according to the base metal, WZ and HAZ. In addition, the control parameters and the critical criterion of the accelerated growth were proposed, which laid a foundation for the remaining life prediction of the TC2 titanium alloy structures welded by the GTAW.