Formation Of Heat-affected Zone Research Articles

Influence of microalloying on precipitation behavior and notch impact toughness of welded high-strength structural steels

Microalloying elements such as Nb and Ti are essential to increase the strength of quenched and tempered high-strength low alloy (HSLA) structural steels with nominal yield strength ≥ 690 MPa and their welded joints. Standards such as EN 10025–6 only specify limits or ranges for chemical composition, which leads to variations in specific compositions between steel manufacturers. These standards do not address the mechanical properties of the material, and even small variations in alloy content can significantly affect these properties. This makes it difficult to predict the weldability and integrity of welded joints, with potential problems such as softening or excessive hardening of the heat-affected zone (HAZ). To understand these metallurgical effects, previous studies have investigated different microalloying routes with varying Ti and Nb contents using test alloys. The high-strength quenched and tempered fine-grained structural steel S690QL is the basic grade regarding chemical composition and heat treatment. To evaluate weldability, three-layer welds were made using high-performance MAG welding. HAZ formation was investigated, and critical microstructural areas were identified, focusing on phase transformations during cooling and metallurgical precipitation behavior. Isothermal thermodynamic calculations for different precipitations were also carried out. Mechanical properties, especially Charpy notch impact toughness, were evaluated to understand the influence of different microalloys on the microstructure of the HAZ and mechanical properties.

Heat affected zone evolution in fine grained aluminum alloys during laser welding: Phase-field simulation and analytical investigation

One of the biggest challenges in the welding of strengthened alloys by grain refinement is the grain growth phenomenon in the heat-affected zone (HAZ), which would result in the degradation of mechanical properties. The goal of this study is to comprehend the HAZ evolution in the fine-grained aluminum alloy during laser welding as a low heat input process. Spot laser welding of fined grain 1050 aluminum alloy revealed that grain growth and HAZ formation occurred in samples with 4 µm grain size, but no grain growth occurred outside of the fusion line (FL) in larger grain samples. The microstructure of HAZ was simulated using the numerical phase-field technique. The numerical model's findings demonstrated that a critical grain size (Dcr) for the base metal can be established, above which grain growth would not occur outside FL. To predict grain size distribution outside FL, an analytical model was also used. According to both models, as grain size increases, the HAZ width decreases, and above a critical grain size, no HAZ will form outside of FL. In spot welding, Dcr was independent of power density but for continuous welding processes, Dcr has a direct relationship with heat input per unit length of weld. Moreover, HAZ grain growth mainly occurred in heating step for both types of processes.

Impact of Workpiece Position on Pallet during Laser Cutting on Heat-Affected Zone Formation

Impact of Workpiece Position on Pallet during Laser Cutting on Heat-Affected Zone Formation

Application of a high-speed infrared thermographic camera to the study of HAZ softening in S960 welded joints

Hot strip rolling of low-carbon advanced high-strength (AHS) sheet steels is difficult because their products require specific chemical compositions to achieve excellent mechanical properties. The formation of a heat-affected zone (HAZ) during welding is therefore a challenge in terms of maintaining high strength values. This fact complicates the formation of the softening area when the hardness in the HAZ rapidly decreases. According to the continuous cooling transformation diagram (CCT), the chemical composition of the base metal is directly related to the fine-grained martensitic microstructure arising from very high cooling rates and microalloying up to 0.2 wt% by Nb, V, and Ti. The gas metal arc welding (GMAW) was used to perform the study, what presents a challenge for thin sheets because of very narrow HAZ formation, suscepible to HAZ softening phenomenon. The width of the HAZ was about 6 mm and determined by applying an infrared thermographic camera to measure the real-time temperature development. The significant reduction in microhardness, known as the softening phenomenon, occurred in the intercritical heat-affected zone or at the boundary between intercritical and subcritical HAZ, according to real-time diagnostics of the temperature development and the microhardness results. The amount of heat produced during welding plays an important role in this context and is directly connected to the heat input of the welding process. The softening area can be reduced and its impact on the mechanical properties can be lowered by appropriately modifying the welding conditions, e.g., optimising the heat input. The purpose of this paper is to point out the change in temperature during the welding process.

Evaluation and Prediction of Formation of Heat-Affected Zone and Mechanical Properties According to Welding Method of STS 316L/A516-70N Clad Plates

Two welding methods of FCAW (Flux-cored arc welding) + FCAW, and FCAW + GTAW (Gas tungsten arc welding) were compared to identify effective routes for STS 316L/A516-70N clad stainless steel. Since the welding speed of the FCAW + GTAW welding method is slower than that of the FCAW + FCAW welding method, the amount of heat input is large, the size of the heat-affected zone formed is larger, and the amount of angular deformation is also large. The microstructure and deformation of the welding specimens were investigated by computational simulation, and the results were compared with calculated results for actual specimens. The results were very similar, thus confirming the high accuracy of the calculation. After measuring the hardness value of the actual welded specimens, the specimen welded by the FCAW + FCAW welding method was found to have a higher hardness value. The hardness of the welded portion of the FCAW + GTAW specimen tests tended to remain at nearly the same value throughout the specimen, indicating that the FCAW + GTAW hardness profile is desirable. In the computer simulation, butt welding was used to set the optimal heat source conditions for the two welding methods, and the effect of heat formed during welding was confirmed using the thermal analysis results according to the conditions. Based on the butt welding conditions, the residual stress and strain for the two welding methods are discussed, using calculations for the welding of C-seam (circumferential seam) and L-seam (longitudinal seam) used in the manufacture of pressure vessels.

Investigation of the Microstructure of Ti6Al4V Alloy by Coaxial Double Laser Metal-Wire Deposition.

Laser metal-wire deposition (LMwD) exhibits a larger molten pool and layer height during printing, compared to powder bed fusion additive manufacturing; in the present study, these features revealed a more inhomogeneous but easily observable microstructure. The coaxial double laser used herein makes the energy distribution of the molten pool more complex than that afforded by a single laser source, and the microstructure of the LMwD parts was more heterogeneous as well. We observed the microstructure of Ti6Al4V by the double LMwD as-built samples by conducting a laboratory experiment and a simulation. The precipitated martensite (α') phase was defined after eliminating the influence of the β element in an X-ray diffraction analysis, which has not been discussed previously in the literature. We also propose a theory regarding the formation of heat-affected zone (HAZ) bands in an environment that includes the α' phase. Our experiments revealed only white HAZ bands, which can be attributed to the solute partitioning caused by sequential thermal cycling and the absence of the β element. The microhardness of the HAZ band areas was lower than that of both the upper and lower sides. The simulation results indicate that the maximum temperature of 2925 °C restrains the generating of HAZ bands in the final two deposited layers, due to its great difference from the β transus temperature. Moreover, the higher heat accumulation in the upper layers promoted the migration of β-grain boundaries, which may explain why the coarse columnar β grains tended to grow at the edge area in the layers deposited later. We also observed that with the use of high temperature, the nucleation of β grains is more easily promoted in the lower layers. We conclude that the concentration of residual stress in the fusion zone and the first layer is favorable to the nucleation of equiaxed grains.

Effect of the meltdown on thermoplastic joint produced by quasi-simultaneous laser transmission welding

This study aims to investigate the effect of the polymer pair meltdown process and mechanical properties using three different laser transparencies 20%, 30% and modulated, ranging from a minimum 27% to a maximum 47%. The cross-sections of joints were analysed with an optical microscope. Burst pressure was performed to evaluate the strength of welded joints produced with different laser welding process parameters. Welding parameters, scanning speed and meltdown were varied and their influence on the quality of the polymer joint was recorded and evaluated. With the increase of meltdown, a more molten volume of polymer can be seen in the cross-section area. It was shown that with the increase of meltdown, the formation of pores occurred due to the high energy concentration obtained within each laser scan passing across the weld seam. The decrease of burst pressure in all polymer pairs was observed with 0.33 mm and 0.34 mm targeted meltdown. Burn marks and burned lines were observed in joints with 20% laser transparency. Modulated laser transparency influenced non-homogeneous temperature distribution inside the joint, which influenced the formation of heat-affected zones (HAZ) and pores. A study of the influence of cooling time on joint formation showed that it is possible to variate total meltdown while changing cooling time until the joint is solidified. • Within the increase of meltdown, bigger weld flash occurred inside weld seam. • Peak weld strength observed at specific meltdown values. • The decrease of weld strength is influenced by defect formation inside seam. • Non-homogeneous melting, HAZ observed with modulated laser transparency polymers. • Total meltdown can be controlled by modulating cooling time.

Interactional relations between ablation and heat affected zone (HAZ) in laser cutting of glass fiber reinforced polymer (GFRP) composite by fiber laser

Laser technology is widely used in the processing of various composite materials. Ablation and heat affected zone (HAZ) are important phenomena in laser processing, but the relationship between ablation and HAZ defects has not been deeply researched. In this paper, laser cutting of glass fiber reinforced polymer (GFRP) was investigated by means of fiber laser. To assess the influence of the process parameters on ablation and HAZ, four main parameters were selected as the experimental factor in single factor experimental study. The degree of material ablation was judged according to the phenomenon of light spot and plume in processing, and the width of HAZ was measured by optical microscope. The experimental analysis shows that the HAZ defects by the ablation phenomenon can be evaluated to reveal the relationship between ablation and HAZ. On this basis, improving the ablation condition is helpful to reduce the formation of HAZ.

Surface morphology and microstructure of the hole sidewall during drilling of Polyether-Ether-Ketone(PEEK) via single-pulse laser

Polyether-ether-ketone (PEEK), as one kind of thermoplastic polymers, exhibits a great deal of remarkable properties and plays an important role in aerospace, electronics, automotive and medicine. An investigation of single-pulse laser drilling on Polyether-ether-ketone (PEEK) was reported to show the influence of irradiation energy on the hole sidewall. In-situ evolution of drilling process was observed by the high-speed camera. The surface morphology and microstructural characteristics of the hole sidewall were evaluated by different characterization techniques. The hole sidewall was divided into three parts: expanded zone at the entrance, linear zone in the middle, and U-shaped zone at the bottom. It was found that the quality of inner sidewall could be obviously improved under high single-pulse energy (>1 J), in terms of the surface morphology with small heat-affected zone (HAZ) thickness and surface roughness, as well as the least adhesion. Besides, chemical and structural characteristics of the hole sidewall changed a lot under high energy. The C content of three parts increased as the energy increased. The crystallinity of the hole sidewall decreased from 35 % to 25 % after laser-energy irradiation, but there was little change under different single-pulse energy. New diffraction peaks appeared in X-ray diffraction images and the intensity of the relative peaks in Raman spectra decreased when the energy was over 1 J. It was proven that some chemical bonds (phenyl ring (1597 cm−1) and C–O–C (1148 cm−1)) would break under high energy, contributing to mass removal of the keyhole. Moreover, the HAZ thickness of the hole sidewall was calculated based on a viscous flow model, which showed a good consistency with experimental results. These results reveal material-removal mechanism accompanying the appearance of direct decomposition of the material and breaking of chemical bonds under high energy. It can provide references for understanding mechanisms of HAZ formation and material-removal and improving surface quality for laser drilling of polymers.

Performance Measurement and Discharge Data Based Analysis of Ultrasonic Assisted μEDM for Ti6Al4V

Abstract Unconventional machining of difficult-to-cut conductive materials with high accuracy, low heat-affected zone formation, and the ability to cut intricate geometries entitles micro-electrical discharge machining (μEDM) as the most versatile technology in micromachining. Ultrasonic vibration assistance further enhances the material-removing ability of the μEDM process while imparting several other benefits. The present work proposes a comparative study between the unassisted and ultrasonic vibration assisted μEDM to the tool electrode for machining microslots on Ti6Al4V material using an in-house developed tool holder. The characteristics of the discharge waveforms were captured using a data acquisition system at high sampling rates. The pulse discrimination system is used to perform an in-depth study of the discharge pulses. μEDM milling experiments were performed to machine microslots at varying input voltages, capacitances, and feed rates. The ultrasonic vibrations proved beneficial in addressing the primary issue associated with the μEDM process, i.e., the material removal rate (MRR) with a maximum of 35% increment. Applying ultrasonic vibrations reduced the recast layer and tool wear rate (TWR) and increased the surface finish.

A fuzzy finite element model based on the eigenstrain method to evaluate the welding distortion of T-joint fillet welded structures

T-joint fillet welded structure is one of the most commonly welded structures in the assembly of vessels, so it is crucial to accurately predict the welding distortion of T-joint fillet as fast as possible for in-process quality controls in ship building industry. Eigenstrain distribution which forms after welding accounts for the appearance of welding distortion, the results obtained from experiment and thermal elastoplastic finite element (FE) analysis indicate that it is closely related with the formation of heat-affected zone (HAZ), however, a quantitative description needs to be determined based on limited experimental data. To deal with this problem, a fuzzy finite element model (fFEM) is proposed to evaluate welding distortion in T-joint fillet welding using the eigenstrain method. A set of coefficients which determines the eigenstrain distribution is introduced as the optimization parameters in fFEM. The optimized coefficients of eigenstrains can be found by introducing the genetic algorithm (GA) and combining it with the commercial FE software ANSYS. The eigenstrain distribution calculated by the optimized coefficients can predict the welding distortion with high accuracy and efficiency, the same optimized coefficients and corresponding eigenstrain distribution can be applied to various dimensions of T-joint welded structures if the welding parameters remain unchanged.

Effect of Mn/N ratio on microstructure and mechanical behavior of simulated welding heat affected zone in 22% Cr lean duplex stainless steel

The effect of Mn/N ratio on microstructural evolution, mechanical and fracture properties in welding heat affected zone (HAZ) of 22% Cr lean duplex stainless steel (DSS) were investigated. At comparative low heat inputs for low nickel tested DSS, the reformed austenite evolution of HAZ was mainly controlled by N content, and increasing Mn/N ratio promoted the growth of widmanstatten austenite (WA) and inhibited Cr2N precipitates formation in HAZ, and then significantly reduced its strength and elongation due to weakened strengthening effect and the decrease of austenite fraction. The tensile and yield strength of HAZ for 17.80 Mn/N ratio DSS are higher than that of 2205 DSS, but the obstruction of dislocation movement resulted in a sharp decrease of plasticity at high heat input of 2.935KJmm-1. The impact fracture of HAZ changed from ductile to brittle mode with the increase of Mn/N ratio, and for 17.80 Mn/N ratio DSS with high nitrogen content, the widening gaps of hardness and elastic moduli between two-phases in HAZ increased crack tendency, and significantly reduced its toughness. More grain boundary austenite (GBA) and WA formation for 51.14 high Mn/N ratio DSS segmented and refined the ferrite matrix in HAZ and improve impact toughness at higher heat input, while the coarsening of WA and (Cr, Mn) O oxides adversely reduced it to a lesser extent.

Numerical simulation of laser micro drilling of polymethyl Methacrylate

Laser micro-material processing (LMM) is a good choice for producing intricate features like cooling holes in turbine blades, cardiac stents, Microfluidic channels, Micro-via, inkjet printer nozzle, biomedical catheter holes, thin-film scribing, and micro-electro-mechanical system (MEMS) fabrication. PMMA (polymethyl Methacrylate) has a wide usage for biomedical applications due to its non-toxic nature, ease of processing, biocompatibility, and reliability. A focused laser beam removes material by localized melting and evaporation in laser micromachining. LMM is a thermal energy-based process with thermal stresses, heat-affected zone formation, and recast layer. This paper uses a 2D axisymmetric model to investigate the effects of laser micro-drilling process parameters on PMMA using COMSOL Multiphysics 5.2. The laser beam profile is Gaussian, and the laser beam was modelled as a moving heat source. Temperature distribution and the heat-affected zone for different incident laser powers were evaluated.

Experimental investigation of creep crack growth behavior in the heat affected zone of boron added modified 9Cr–1Mo steel weld

Abstract This study aims to quantify the improvement in the creep crack growth (CCG) resistance in the heat-affected zone (HAZ) of boron added modified 9Cr–1Mo (P91B) steel weld at 898 K. The crack growth rates in the HAZ of P91B weld have been compared with the crack growth rates in HAZ of without boron P91 steel weld. The creep crack growth rates are estimated as per ASTM E1457 using 7 mm thick compact tension specimens with a notch in the HAZ and test duration 248h-11,000 h. The CCG rate ( a ˙ ) vs. C* correlation, commonly expressed as a ˙ = D ( C ∗ ) ϕ , has been established. In comparison, the crack growth rate in the HAZ of P91 weld is found to be threefold as compared to HAZ of P91B weld; with the difference in CCG rate increasing towards a higher C* range. Creep damage assessment study has been done in the vicinity of creep crack in HAZ of a P91B weld specimen tested for 11,000 h. The extent of cavitation, cavities link-up, and micro-crack formation in HAZ of P91B weld is found to be relatively lower than HAZ of P91 weld. Most of the cavities appear to be discrete in nature. This testifies improvement in the creep crack growth resistance in the HAZ of P91B weld due to controlled boron addition of about 100 ppm to modified 9Cr–1Mo steel.

The 3D surface morphological investigation of laser cutting process of 2024-T3 aluminum alloy sheet

In laser cutting, process parameters have a significant effect on the surface properties of the material. The paper is concerned with the laser cutting process of the 2024-T3 aluminum alloy sheet. Laser power (1800 W, 2600 W, 3400 W) and cutting speed (3.5 m/min, 5 m/min, 6.5 m/min) were determined as process parameters, and the cutting process of 2 mm thick 2024-T3 aluminum alloy sheet was performed on the laser cutting machine. After the cutting process, surface morphology and heat-affected zone formation were examined by using an optical microscope and optical profilometer, and hardness measurement was carried out. The cutting is not performed at low laser power and high cutting speeds. The higher cutting speeds result in lower surface quality. The results highlighted that the optimum cutting parameters should be chosen. The highest quality cutting is realized at 2600 W - 5 m/min process parameters.

INVESTIGATION OF THE INFLUENCE OF PREHEATING ON THE STRUCTURE AND PROPERTIES TRANSITION ZONE BETWEEN HARDFACED WEAR-RESISTANT ALLOY AND 55NICRMOV5 STEEL

The results of the experimental studies hardfacing of the 55NiCrMoV5 die steel of the three types of wear and heat-resistant alloys with preheating are presented. The effect of the preheating on the structure hardfaced alloys as well as on the heat affected zone formation of the base metal is estimated. It is revealed that the use of preheating under the considered conditions of surfacing causes the formation of a structural heterogeneity of the heat-affected zone of the base metal, which manifests itself as a variable distribution of chromium and molybdenum.

Influence of discharge energy on the properties steel alloy after EDM

In this comprehensive study, the influence of discharge energy of the EDM process was correlates with the formation of heat-affected zone (HAZ) depth in 40CrNi steel alloy. The change in micro-hardness distribution of the treated surface measured cross-sectionally from the machined surface and represented the extent of HAZ. The orthogonal central composite design methodology was used to conduct the experiment. An empirical model has presented the relationship between the EDM discharge energy and the depth of the heat-affected zone. It was found that the change in the surface layer after EDM reduces the fatigue life of samples up to 30% as compared to the sample prepared by the conventional turning process.

The effect of the initial microstructure of the X70 low-carbon microalloyed steel on the heat affected zone formation and the mechanical properties of laser welded joints

In this paper, the heat affected zone (HAZ) of laser welded joints of the X70 steel were studied by the transmission electron microscopy method. The effect of the initial microstructure (coarse-grained hot-rolled and fine-grained after cross-helical rolling) on the HAZ formation and the mechanical characteristics of the welded joints were shown. It was found that the microstructure in the inter-critical HAZ of the steel after cross-helical rolling was more dispersed, homogeneous, and uniform compared to that of the coarse-grained hot-rolled one due to the initial fine-grained ferrite-bainitic-pearlite microstructure and the absence of pronounced ferrite-pearlite banding in the base metal. The character of the microhardness value distribution in the HAZ of the steel after cross-helical rolling was smooth with the gradual decrease from 370 down to 185 HV as shifted towards the base metal. In the HAZ of the coarse-grained hot-rolled steel, the heterogeneous microhardness value (up to 640–670 НV) distribution was revealed. The reason was the upper degenerate bainite microstructure with high residual stresses, characterized by laths up to 2.0–2.5 μm long and a high martensitic-austenitic constituent fraction (10–16%) of a slender shape along the boundaries of bainite laths. The conclusion was drawn that one of the ways to reduce the brittleness of the laser welded joints could be using the initially fine-grained steels possessing the homogeneous (mainly bainitic) microstructure.

Effect of welding processes and heat input on corrosion behaviour of Ferritic stainless steel 409M

In the present work, Ferritic stainless steel 409M is welded with shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) of welding current 90A, 100A and 110A. Four mm thick plates were used as base material and single V-joint was prepared for welding. Single pass welding was carried out. Microstructures in the transverse section were observed for base metal, Heat Affected Zone (HAZ) and weld joint. Corrosion rate of welded joints have been evaluated by weight loss method in sodium chloride (NaCl) solution. In this investigation results reveal that, corrosion rate of welded joint is more than the base metal. It is also found that corrosion rate increases on increasing welding current. It is observed that corrosion rate is more in SMAW than GMAW and GTAW weld joint. Results are discussed in the light of microstructure. Increased corrosion rate is attributed to welded structure and formation of HAZ due to variable welding heat input.

Multi-pass laser cutting of carbon/Kevlar hybrid composite: Prediction of thermal stress, heat-affected zone, and kerf width by thermo-mechanical modeling

Numerical modeling offers considerable promise to reduce costs associated with trial-and-error process in the manufacturing industry. In laser cutting of fiber-reinforced composites, the developed thermal stress in the cut region has considerable influence on the application of the machined composite and the end product quality. Nevertheless, measurement of the thermal stress is quite challenging in practice. Here, an uncoupled thermo-mechanical finite element model is developed to accurately predict formation of heat-affected zone, kerf width, thermal field, and thermal residual stress of an anisotropic carbon/Kevlar fiber reinforced composite during multi-pass laser cutting process. A novel approach of element deletion incorporating temperature-dependent Hashin failure criteria and VUMAT subroutine is proposed. The study is carried out using Abaqus interlinked with Fortran compiler to define laser Gaussian beam (DFLUX subroutine) and material removal (VUMAT subroutine) for determining the temperature gradient and cut characteristics, respectively. The numerical results agree well with the experimental scanning electron micrographs of heat-affected zone and kerf width. In addition, residual temperature after subsequent pass results in greater temperature distribution and heat accumulation. It has also been established that the strength of composite gradually decays with the increase of temperature due to stiffness (elastic moduli) degradation in the area of the cutting zone, accelerating damage initiation in both fibers and matrix.