Heat Affected Zone Material Research Articles

Investigation on the fatigue crack growth behavior of welded joints in EH690 high-strength marine steel

EH690 high-strength steel (HSS) is extensively utilized in marine engineering due to its exceptional strength. The fatigue crack growth (FCG) behaviors of EH690 HSS welded joints in different zones (base metal (BM), heat-affected zone (HAZ), and weld metal (WM)) were investigated by conducting FCG tests with various stress ratios (R). The results demonstrate that the WM and HAZ materials exhibit enhanced resistance to FCG compared to the BM material. The higher stress ratios result in increased fatigue crack growth rates (FCGRs). The welded residual stress (WRS) distribution in the welded joints was predicted considering solid-state phase transformation (SSPT). Subsequently, a comprehensive analysis of the WRS influence on FCG behavior shows that the residual compressive stress enhances the material’s resistance to FCG. Additionally, the effect of R on the FCG behavior of the material was investigated by employing the Walker model, and the applicability of the Walker model was discussed as well. Finally, the FCG mechanisms of the different zones in the welded joint were investigated from a microscopic perspective, further exploring the influence of R on the FCG behavior.

Combined Gleeble physical welding simulation and low-cycle thermo-mechanical fatigue for heat-affected zone material for 9Cr steel: Experimental testing and through-process model

Combined Gleeble physical welding simulation and low-cycle thermo-mechanical fatigue for heat-affected zone material for 9Cr steel: Experimental testing and through-process model

Selected properties of X120Mn12 steel welded joints by means of the plasma-MAG hybrid method

The article describes properties of welds made of high wear resistance X120Mn12 steel obtained by the hybrid PTA-MAG (plasma transferred arc – metal active gas) method. The specimens were 8 mm thick rectangular (200 mm × 350 mm) sheets metal. The analyzed butt welds were made with the parameters selected according to the criterion of smallest cross-sectional area of welds and the narrowest HAZ (heat affected zone). The outcome of metallographic tests of weld, HAZ and parent material, hardness distribution and XRD (X-ray diffraction) patterns of selected areas are presented. The IIT (Instrumented Indentation Test) method was used to describe the distribution of mechanical properties shaped by thermal cycle annealing of the welding process. The investigation shows that the application of the PTA-MAG hybrid heat source for welding manganese steel enables the use of the filler material ER307 (AWS-A5.9). The hybrid PTA-MAG welding system has the relatively high potential to be an efficient alternative to welding standard processes for X120Mn12 steel due to the HAZ overheating limitation. The zone of high-risk weld cracking is the part of the HAZ close to the fusion area that has been reheated during weldment formation. Heat input about 0.6 kJ/mm is needed to provide full deep penetration butt weld without defects and with a vapor capillary of wide enough to cover the weld gap. The increase of hardness in the welded joint is smooth distributed and going up to 10% compared to the base material. The width of HAZ was <1 mm. Intensive carbides precipitation in HAZ has been avoided successfully.

Microstructure and Impact Toughness of Laser-Arc Hybrid Welded Joint of Medium-Thick TC4 Titanium Alloy

This study delves into the impact toughness of medium-thick (12 mm thick) titanium alloy joints crafted through a multi-layer, multi-pass welding technique that blends laser-arc (MIG) hybrid welding technology. Microstructural scrutiny, employing optical microscopy, SEM and TEM, unveils a consistent composition across weld passes, with prevailing α/α′ phases interspersed with some β phase, resulting in basket-weave structures primarily dominated by acicular α′ martensite. However, upper regions exhibit Widmanstatten microstructures, potentially undermining joint toughness. Hardness testing indicates higher values in cosmetic layers (~420 HV) compared to backing layers and bending tests manifest superior toughness in lower joint regions, attributed to smaller grain sizes induced by repetitive welding thermal cycles. Impact toughness assessment unveils diminished values in the weld metal (WM) compared to the heat-affected zone (HAZ) and base material (BM), amounting to 91.3% of the base metal’s absorption energy. This decrement is ascribed to heightened porosity in upper regions and variations in grain size and phase composition due to multi-layer, multi-pass welding. Microstructural analysis proximal to failure sites suggests one mechanism wherein crack propagation is impeded by the β phase at acute crack angles. In essence, this study not only underscores the practicality of laser-MIG hybrid welding for medium-thick TC4 alloy plates but also underscores the reliability of joint mechanical properties.

High-cycle rotating-bending fatigue performance of S690QL welded joints

In recent decades, high-strength steels have become increasingly popular in the construction industry. Materials like S690QL steel are mainly characterised by their enhanced mechanical properties, including high yield and tensile strength. As a result, this leads to improved performance, durability, and safety of steel components, making such materials commonly used in several offshore applications due to their exceptional strength and cost-efficiency. Within the offshore industry, the most critical connections are usually the welded joints, thus rising significant concerns regarding the characterisation of the material in the area close and affected by the welding process. Furthermore, this material is highly prone to the appearance of cold cracks. To address these issues, rotating-bending fatigue tests were successfully conducted on S690QL steel to evaluate and compare the fatigue life within different regions of the investigated welded joints, specifically the weld material, heat-affected zone and base material. Increasing thickness of the weld plates was found to have a negative impact on the fatigue resistance, which aligns with the lower static strength for the thicker case. Also, variations in fatigue strength across the thickness were observed. The heat-affected zone exhibited a heterogeneous microstructure, leading to increased fatigue variability during testing, but the fatigue resistance observed aligns with the findings in the literature for comparable steel grades. Detailed experimental results are presented, particularly regarding this heat-affected zone, where the majority of fatigue failures occur, which provide bases for the development of new normative material-scale SN curves.

Miniature specimen tests and fracture model of heat affected zone material

AbstractThe paper investigates the mechanical properties of the heat affected zone (HAZ) material near welds and compares the properties to those of the base metal and weld materials. A dedicated experimental set‐up was designed and manufactured to test miniature specimens with a cross‐section width in the range of 1 mm to 2.5 mm and a parallel gauge length of less than 10 mm. To identify the HAZ of the welded connections, a macro‐etching technique was adopted, and the shape and size of the HAZ were measured. Afterwards, miniature specimens were extracted from the base metal, weld and HAZ in both the longitudinal and transverse directions of the weld, and subsequently tested in the specialised experimental set‐up. The miniature specimens not only included the normal rectangular plate‐type specimen, but also the notched round bar and grooved plane strain types of specimens. Hence, the stress‐strain curve and fracture strains under various stress states were obtained from the tests. The validity of the Lode angle Modified Void Growth Model (LMVGM) was investigated using the experimental data, and the fracture loci of the base metal, weld and HAZ in both the longitudinal and transverse directions were identified.

Damage Assessment of Similar Martensitic Welds Under Creep, Fatigue, and Creep-Fatigue Loading

Abstract For the assessment of welds under high-temperature conditions in the creep or creep-fatigue regimes, the knowledge of the damage location and its temporal evolution is of high importance. The local failure behavior of weld joints is not reflected in design guidelines using weld reduction factors or in typical assessment approaches. The evaluation of local strains and stresses in the heat affected zone (HAZ) is essential for a more detailed consideration of weld behavior and has a high potential for improvement of design and inspection guidelines. In this paper, an overview of current developments in the assessment of weld joints is given. Uni-axial creep, component tests, low cycle fatigue (LCF), and creep-fatigue experiments with base material, weld joints and microstructure simulated HAZ material are presented. The use of test results of microstructure simulated HAZ material allows the parameter identification of numerical material models for the HAZ and improves the simulation of the local stress and strain behavior of weld joints. Two assessment methods, one for creep and one for fatigue/creep-fatigue were presented, based on the local behavior determined by the numerical simulations. The assessment approach for pure creep loads was validated using several uni-axial creep tests and two component tests. The approach for the fatigue/creep-fatigue loads is still in the developmental stage but the first results were presented and further areas for improvement were identified.

Constitutive model of duplex stainless steel S22053 and its weld under cyclic large plastic strain loading

This study investigated the mechanical properties and constitutive models of duplex stainless steel S22053 under cyclic large plastic strain loading. To this end, smooth round bar specimens of the base metal, deposited metal, and heat-affected mixing zone material were tested under monotonic tensile loading and cyclic loading. Furthermore, the failure modes and stress–strain curves of the specimens were analysed. Based on the test results of the smooth round bar specimens under cyclic symmetric constant amplitude and monotonic tensile loading, the N3L1 and S10 parameters of the Chaboche model for duplex stainless steel S22053 were calibrated, respectively. Then, the accuracy of the calibrated Chaboche model was verified against the test results of the smooth round bar and circular notched bar specimens. The results showed that the base metal and heat-affected mixing zone material have higher ductility, and the strength of the deposited metal is the highest. Furthermore, the N3L1 parameters can accurately simulate the behavior of smooth round bar specimens under cyclic medium plastic strain loading, while the S10 parameters are more suitable for simulating the mechanical response of circular notched bar specimens under cyclic large plastic strain loading. The accuracy of the Chaboche model depends on the matching of the loading strain range of the test data for calibrating the model with that of the simulation cases. The results of this study provide fundamental data for analysing the seismic and ductile fracture performance of duplex stainless steel and its welded structures.

An Experimental and Numerical Study on Aluminum Alloy Tailor Heat Treated Blanks

Information is presented on the conceptualization, experimental study, and numerical process simulation of tailor heat treated aluminum alloy blanks. This concept is intended to improve the forming behavior of aluminum parts in challenging conditions. The implementation requires precise control of laser heat treatment parameters within a suitable industrial framework. The study details material properties, heat treatment parameters, and experimental results for the strength and elongation properties of an AA6063-T6 aluminum alloy. Constitutive modeling is applied using the Hocket–Sherby equation, which allowed us to establish a correlation between laser heat treatment maximum temperature and the corresponding material softening degree. Based on the generated flow stress–strain curves, a numerical simulation of a representative case study was performed with Abaqus finite element software highlighting potential improvements of tailor heat treated blanks (THTB). The influence and effectiveness of heat-affected zone (HAZ) dimensions and material softening were analyzed.

Effect of welding current on properties of activated gas tungsten arc super duplex stainless steel welds

Abstract A comparative evaluation of the influence of welding current on Tungsten Inert Gas (TIG) welding and Activated Tungsten Inert Gas (ATIG) welding on the depth of penetration and microstructure properties was performed. Various super duplex stainless steel (SDSS) beads on plate weld joints were studied. Visual observation showed that lower welding current resulted in partial weld penetration in the case of both TIG and ATIG weldments. Weld joints obtained by the ATIG process have a higher depth of penetration and depth/width ratios than weld joints obtained in the conventional TIG process at comparatively lower welding currents. Further, microstructural characterizations were performed using optical microscopy. The weld zone microstructure consists of grain boundary austenite (GBA), widmanstätten austenite (WA) and intragranular austenite (IGA). Ferrite percentage in bulk material and each weldment was measured using ferrite scope. The TIG-welded heat affected zone (HAZ) joints showed higher ferrite content than activated flux TIG-welded HAZ joints for various welding current conditions. Ferrite content measured in the weld-zone, HAZ and base material was within the ranges of the standard values. The TIG weld zone showed higher hardness than that of the ATIG weld zone.

Flash butt welding corrosion of mooring chains

ABSTRACT Flash butt welding is a resistance welding process that offers great advantages due to its high thermal efficiency, simplicity and high speed, makes it ideal for welding mooring chains. Despite its advantages, numerous corrosion problems are still being found in practice, both in the heat-affected zone and the weld line. Literature is scarce about it, limiting mostly to state the problem. The majority of the studies attribute this preferential corrosion to local changes in the microstructure that induce a galvanic coupling effect. Mooring chain R3 grade steel with preferential corrosion along the weld line has been studied from both metallographic examinations and electrochemical methods. Small differences were found in the microstructure of the heat-affected zone and base material (mainly composed of tempered martensite) but nevertheless, significant with respect to its corrosion behaviour. The corrosion mechanisms are discussed with particular attention to the electrochemical differences around the welding line.

A method for determining the constitutive model of the heat-affected zone using digital image correlation

The heat-affected zone (HAZ) is an unmelted region of a welded joint that has changed in material properties because of high temperatures during the welding process. HAZ has a lower strength than the base (parent) material (BM) and the weld metal (WM). The lower material strength is more significant if BM is made of high strength steel and the undermatching filler metal is used. Therefore, the constitutive model of HAZ is essential for predicting the mechanical behaviour of the welded joint. In this paper, a method for determining the true stress–strain relationship of HAZ is proposed. The effect of the transverse constraint on the longitudinal deformation of HAZ imposed by BM and/or WM is eliminated by a linear modification factor correlating to the true strain. Standard tensile coupon tests were used to obtain the constitutive model of HAZ using digital image correlation (DIC). The modification factor proposed for reducing the true stress is calibrated based on finite element analysis (FEA). The modified constitutive model of HAZ is validated against the experimental results obtained by DIC. The validated HAZ material property can be used in advanced numerical simulation of welded joints.

Experimental and Numerical Investigations of the Deep Rolling Process to Analyze the Local Deformation Behavior of Welded Joints

Welded joints show a comparably low fatigue strength compared to the base material. Thus, different post-weld treatment methods are used to enhance the fatigue strength of welded joints. A promising method to enhance the fatigue strength of metallic components is the deep rolling process, but this has rarely been applied to welds. For the qualification of the deep rolling process as an effective post-weld treatment method, knowledge about its influence on the surface and subsurface properties at the fatigue critical weld toe is necessary. Here, geometrical and metallurgical inhomogeneities lead to complex contact states between deep rolling tools and weld toes. Thus, for a first analysis of the local deformation behavior during deep rolling of welded joints, experimentally and numerically generated deep rolling single tracks are compared. Cyclic strain-controlled tests to determine the material behavior were carried out for the numerical analyses using finite element simulation. The presented study shows that it is possible to describe the local deformation of welded joints during deep rolling using finite element simulation. A correct depiction of material behavior is crucial for such an analysis. It was shown that certain irregularities in material behavior lead to lower coincidences between simulation and experiment, especially for the investigated welds, where only low differences in hardness between base material, heat-affected zone, and filler material were found.

Improved mechanical properties of laser-repaired 15-5PH stainless steel by in-situ heat treatment and grain refinement

Mechanical properties of repaired part by laser melting deposition (LMD) mainly depend on microstructure of clad layer and heat affected zone (HAZ). For precipitation-hardened steel, the properties of as-deposited materials are usually not satisfactory. Post heat treatment is an effective way to improve mechanical properties but sometimes become infeasible or restricted due to various reasons. In this paper, by deliberately reducing the scanning speed to provide more energy than needed to melt the powder, heat accumulation in the deposited area is enhanced and an in-situ heat treatment is provoked. The strength of as-deposited clad layer is greatly enhanced (1290Mpa for ultimate tensile strength) by precipitation strengthening while maintaining good ductility. The possible influences of excessive heat on the HAZ are also evaluated. Experimental results show all the HAZ samples have a slightly lower strength compared to heat treated substrate. Excessive heat input does not deteriorate the strength of HAZ. On the contrary, the ductility of the material in HAZ is enhanced due to the effect of grain refinement and overage. In this way, the as-repaired parts can achieve a higher strength without heat treatment, which provides a new method for the repair of parts that cannot be subjected to post heat treatment.

Control of the bainitic structure for a wear-resisting hard-faced rail track

Abstract Carbide-free bainite with filmlike retained austenite structure has been reported for its higher wear resistance and toughness compared with conventional bainite and pearlite structure. In order to take advantage from such beneficial structure, this study employs the surface welding method with self-shielded wire electrode containing low carbon (0.15 mass%), high silicon, and nickel on two pearlitic rail steels, R260 and R350HT. The preheating temperature and other welding parameters were carefully selected to avoid too high dilution, which leads to martensite formation. The weld metal, heat-affected zone, and base material were investigated by scanning electron microscopy. Microhardness and wear tests were carried out to ensure improved properties after the surface repair. The results show significant improvements in hardness and wear rate in weld metal compared with the base material.

Constitutive Model and Fracture Criterion of Q345 Steel Welded Joints

Welding joint is a key component in steel structure engineering, which is often subjected to complex stress and becomes the weak link of building structure, and different fracture modes may appear under different stress. In this study, the ductile fracture of Q345 steel welded joint was investigated by selecting the base material and heat‐affected zone (HAZ) material. Based on the J–C (Johnson–Cook) fracture model of stress triaxiality factor, a series of round bar specimens were designed for the tensile test, and the variation of minimum diameter and gauge distance was tracked in real time by digital image correlation (DIC) technology, and the cloud map of strain distribution in the whole loading process was obtained. The constitutive model and fracture criterion model of Q345 steel welded joint base material and HAZ material are established through experimental measurement. The results show that the maximum triaxial stress is at the center root of the minimum diameter of the notched round bar tensile specimen, the sudden change of the notched edge will lead to stress concentration, the stress change of the notch section is the most significant, extending from near the notch, the maximum strain is at the root of the notch, and the fracture position appears at the minimum section of the notch. According to the true stress‐strain curve of a standard tensile specimen and the least square method, the values of parameters A, B, and N of the J–C (Johnson–Cook) constitutive model of base material and HAZ material are 379.80, 452.89, and 0.37 and 392.90, 540.61, and 0.49, respectively. The fracture strains of the base metal and HAZ material under different triaxial stresses were measured experimentally, and the J–C fracture model was fitted. The values of failure criterion parameters D1, D2, and D 3 were 1.025, −0.008, and 3.617 and 0.678, −2.689E‐5, and 7.683, respectively. This provides experimental parameters for mechanical properties and fracture models of welded joints in structural engineering, refined finite element models considering material failure for structural numerical analysis, and basic data for evaluation and design of building structures, which have good social and economic benefits.

In situ absorption synchrotron measurements, predictive modeling, microstructural analysis, and scanning probe measurements of laser melted Ti-6Al-4V single tracks for additive manufacturing applications

In this work, the fundamental processing-structure-property (PSP) relationships that govern laser-based additive manufacturing were investigated with the Ti-6Al-4V alloy. X-ray synchrotron imaging carried out in conjunction with in-situ integrating sphere radiometry enabled real-time energy absorption measurements for a range of melting conditions that varied laser power and velocity. A thermal conduction model that incorporated the in-situ absorption data and final melt pool geometry was used to predict the thermal histories and diffusion distances along the heat-affected zone (HAZ) in the Ti-6Al-4V alloy to provide insight into the solid-state phase transformations that occurred in the unmelted regions adjacent to the melt pool. Resulting microstructural features were quantified using scanning electron microscopy techniques to elucidate changes in solidification behavior. Significant changes to α/β-Ti phase fractions were measured in the unmelted HAZ, across all test cases. Nanoindentation and scanning probe microscopy revealed differences in the hardness, modulus, and Volta potential across the resolidified melt pool, HAZ, and wrought base material. These measurements and simulations can be used to predict how processing changes lead to differences in the as-built performance of titanium parts that are used in aerospace and biomedical applications. This work demonstrates the utility of coupling in-situ absorption data with a conduction-only high speed model, which leads reasonable agreement with the synchrotron imaging measurements and microstructural transformations observed herein.

Investigation on shearing strength of resistance spot-welded joints of dissimilar steel plates with varying welding current and time

The present research investigated the effects of welding current and welding time on the shearing strength of resistance spot-welded joints of low carbon steel and stainless steel plates. The macro characteristics, microstructure and micro-hardness of welded joints were also examined. It was found that the welded joints produced with a welding current of 10 kA and welding time of 80 ms showed the highest shearing strength. The diameter of welded joints and nuggets increased with increasing welding current and welding time. For evaluation of the microstructure, different regions including the nugget, coarse heat-affected zone, fine heat-affected zone and base materials were observed within the welded joints. Also, the nugget and coarse heat-affected zone showed higher hardness than the fine heat-affected zone and base materials due to the presence of martensite. The findings obtained in this research are applicable in the development of resistance spot welding processes for joining dissimilar steel plates.

Modelling of hardfacing layers deposition parameters using robust machine learning algorithms

The study presents a data-driven framework for modelling parameters of hardfacing deposits by GMAW using neural models to estimate the influence of process parameters without the need of creating experimental samples of the material and detailed measurements. The process of GAS Metal Arc Welding (GMAW) hardfacing does sometimes create non-homogenous structures in the material not only in deposited material, but also in the heat-affected zone (HAZ) and base material. Those structures are not fully deterministic, so the modelling method should account for this unpredictable component and only learn the generic structure of the hardness of the resulting material. Artificial neural networks (ANN) were used to create a model of the process using only measured samples without any knowledge of equations governing the process. Robust learning was used to decrease the influence of outliers and noise in the measured data on the neural model performance. The proposed method relies on modification of the loss function and several of them are compared and evaluated as an attempt to construct general framework for analysing the hardness as a function of electric current and arc velocity. The proposed method can create robust models of the hardfacing layers deposition or other welding processes and predict the properties of resulting materials even for unseen parameters based on experimental data. This modelling framework is not typically used for metallurgy, and it requires further case studies to verify its generalisability.

Welding-induced yield strength heterogeneity in X100Q: Modelling and characterisation

Yield strength (YS) heterogeneity in X100Q high strength low alloy (HSLA) steel welded joints is a key factor which influences fatigue life performance. The effects of welding-induced microstructural changes are investigated using a mechanistic YS model, which enables understanding of the key strengthening mechanisms which give rise to YS heterogeneity in X100Q. The model is used to predict YS in parent metal, physically-simulated fine-grain heat-affected zone material, and inter-critical heat-affected zone material, incorporating cooling rate effects. The model successfully predicts the measured welding-induced YS heterogeneity, with high-angle boundary (HAB) and precipitate strengthening mechanisms as dominant factors.