Showing papers on "Heat-affected zone published in 2022"

Experimental study on application of gas metal arc welding based regulated metal deposition technique for low alloy steel

Abstract: ABSTRACT In this work, a modified and advanced welding technique named regulated metal deposition (RMD) has been implemented for joining ASTM A387-11-2 low alloy steel plates. Mechanical behavior and microstructure of welded joints have been experimentally investigated after the recommended heat-treatment process. The microstructures of welded joints were examined using optical and scanning electron microscopes. Optical microscopy indicated the existence of bainitic and martensitic phases in the base material and weld zone, respectively. Scanning electron microscopy combined with energy dispersive x-ray analysis displayed the presence of martensitic colonies as well as deposits of carbide precipitates in both weldments. The mechanical properties of these weldments, namely micro-hardness, tensile strength, and impact strength were also investigated. A comparative study has also been carried out for the same material using the conventional gas metal arc welding, in which the microstructure and mechanical behavior of regulated metal deposition weldments have been compared to those of gas metal arc weldments. Regulated metal deposition weldments showed better mechanical behavior than the gas metal arc weldments for low alloy steel.

TiO2-Assisted Microstructural Variations in the Weld Metal of EH36 Shipbuilding Steel Subject to High Heat Input Submerged Arc Welding

Abstract: Two simple yet comparable fluxes, CaF2 and CaF2–40 wt pct TiO2, have been employed to engineer shipbuilding steels under high heat input submerged arc welding, aiming to clarify the unique functions demonstrated by incurring TiO2 addition. Compared with pure CaF2, TiO2-containing flux could increase columnar austenite width from 119.2 ± 18.1 to 201.5 ± 32.2 μm. Furthermore, TiO2 could significantly enhance acicular ferrite fraction, which has been primarily enabled by the formation of Ti-bearing inclusions.

Dissimilar laser spot welding of aluminum alloy to steel in keyhole mode

Abstract: Laser spot welding was used for the dissimilar joining of aluminum alloy to steel in the keyhole mode. The results showed that the defocusing amount and laser power had significant influence on the weld formation. The aluminum alloy was prone to the formation of welding defects, such as porosity and cracks in the fusion zone, which resulted in an extremely instable welding process and poor joint strength. In order to improve the weld quality, a copper heat sink was placed under the aluminum alloy, which effectively absorbed the heat of the aluminum alloy and reduced the previous reported welding defects. The influence of laser power, defocusing amount, welding time, and shielding gas on the joint characteristics was also investigated. The microstructure analysis showed that a conelike fusion zone and sparsely distributed Fe-Al intermetallic compounds were formed. Hence, a combination of metallurgical bonding and mechanical interlocking was achieved in the laser keyhole spot welds, enhancing the joint mechanical properties. The joint strength of the laser keyhole spot welds reached 620 N/mm, which was comparable to that obtained in resistance spot welds.

Microstructure and precipitation behaviours of laser clad 7075 aluminium alloy

Abstract: Laser cladding is a promising technique for repairing metal components. However, the extreme thermal conditions introduced by laser heat can lead to complex precipitation behavior in the cladding layer and heat-affected zone (HAZ). In this paper, the laser cladding technique was applied to repair a widely used aircraft structural material - 7075 aluminium alloy. Specimens of the cladding layer, HAZ, and their interface were site-specifically prepared by using focused ion beam (FIB) and micro-manipulator. The microstructure and precipitation behaviours of these regions were characterized individually using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the cladding layer forms various species of precipitates, such as coarse MgZn2 particles, Zn-rich particles, and CuMgZnAl compounds. Coarse inclusions and voids are formed at the interface between the cladding layer and HAZ. In the HAZ, solute redistribution and re-precipitation take place due to the laser heating cycle. The majority of Mg and Zn atoms segregate at grain boundaries in the HAZ, resulting in low Mg and Zn contents in the grain interior. The number density of nano-particles was significantly reduced in the HAZ, compared to the unaffected 7075 aluminium alloy substrate, which explains the strength reduction in the HAZ.

Selected Properties of RAMOR 500 Steel Welded Joints by Hybrid PTA-MAG

Abstract: The paper describes the selected properties of RAMOR 500 anti-ballistic (martensitic structure in the initial state) high yield strength steel (1450 MPa) welded joints produced by the hybrid PTA-MAG (Plasma Transferred Arc - Metal Active Gas) method. The welded elements were metal sheets 6.7 mm thick in a rectangular shape with dimensions of 200 mm x 350 mm. The tested butt weld joints have been made with process parameters selected according to criterion of lowest level of material weakening in the heat-affected zone (HAZ). The results of metallographic research of welds heat affected zone and base material, hardness distribution and XRD patterns of specific areas have been presented. Depth-sensing indentation (DSI) is used in this work to determine the distribution of mechanical properties affected by annealing/tempering by thermal cycle of hybrid PTA-MAG welding process. The investigation results show that the use of hybrid PTA-MAG heat source for welding of martensitic structure steel makes it possible to use high strength steel filler material (yield strength 890 MPa) without of cold cracks high risk. The hybrid plasma based welding method has a potential to become a beneficial alternative to other welding processes for ballistic protection steel due to its high efficiency, reduced amount of weld metal content or limited requirements for a preparation of edges of welded joints. The weakest area of welded joints is part of HAZ located close to the base material which has been secondarily tempered by heat of welding thermal cycle. The heat input about 0,57 kJ/mm required to achieve full penetration butt welded joints with no defects and with wide enough capillary channel to cover the welding gap during welding process. Hardness decrease in that area is about 25% in relation of base material. The width of the softened zone was approx. 4.5 mm.

Studies on softening behavior and mechanism of heat-affected zone of spray formed 7055 aluminum alloy under TIG welding

Abstract: In this investigation, fine micro-zone specimens in the heat-affected zone (HAZ) of TIG welded spray formed 7055 aluminum alloy were obtained by heat treatment method. The softening behavior and mechanism of HAZ of this alloy under single pass TIG welding were investigated. Severe non-uniformities of microstructures and mechanical properties were found, according to which the HAZ was divided into the solid solution zone and the over-aging zone. The most heavily softened area of HAZ occurred in the over-aging zone at the position corresponding to the peak thermal cycling temperature of 230–350 °C. The lowest microstructures value was 105 HV, the lowest tensile strength was about 410 MPa. The elongation was slightly higher than that of the base material. The main causes of softening in the over-aging zone were the dissolution of the coherent precipitate η′ and the growth and coarsening of the non-coherent precipitate η.Thermal cycle temperature in the solid solution zone was about 350–536 °C. Mechanical properties in this zone were higher than those of the over-aging zone. After natural aging, mechanical properties recovered to more than 90% of the base material. Microhardness reached 180 HV and tensile strength reached 570 MPa when the thermal cycle temperature was 450 °C. At the same time, the elongation in the solid solution zone was higher than that of the base material. The high mechanical properties were the results of the combined action of the increased ratio of large angle grain boundaries, the increased solid solubility and the formation of coherent GPI zone.

Microstructure and mechanical properties of heat affected zone of laser-MAG hybrid welded low carbon bainitic steel joints

Abstract: • Laser-MAG hybrid welding of new low carbon bainitic steel was conducted. • SHCCT curve of new low carbon bainitic steel was obtained. • Thermal simulation results could serve as reference for heat input optimization. • The microstructures of micro-zones of the welded joint were investigated. • The relationship between impact property of HAZ and microstructure was discussed. In the study, laser-MAG hybrid welding of low carbon bainitic steel was conducted. The weld formation, microstructure and mechanical properties were investigated. The thermal simulation technology was used to investigate the microstructure evolution of the coarse grain heat affected zone (CGHAZ) under different t 8/5 conditions. Meanwhile, the simulated heat affected zone continuous cooling transformation (SHCCT) diagram of low carbon bainitic steel was developed and the optimized heat input range (6–18 kJ/cm) was obtained. The microstructure in the CGHAZ were lath bainites (LB) with a little granular bainites (GB), and M-A constituents. The average tensile strength of the joint was 714 MPa, reached 92.5% of the base metal. The impact energy of the HAZ was 33.8 J, which was 66.0% of the base metal. The reduction of impact toughness in the HAZ attributed to easier propagation of crack leaded by the M-A constituents and parallel slats within LB.

Development of activated tungsten inert gas welding and its current status: A review

Abstract: ABSTRACT This article attempts to compile a list of recent tungsten inert gas welding advancements (TIG). TIG welding only allows for a few millimeters of penetration depth. This limitation of TIG welding can be overcome by a new advanced TIG technique called activated tungsten inert gas welding (ATIG). This new approach of TIG welding allows up to 8 cm to 12 cm of penetration depth. The demand for activated tungsten inert gas welding (ATIG) has risen in the past few years, and it has been rooted as a viable alternative to subtractive manufacturing. According to research, ATIG weldments have mechanical qualities that are comparable to other more expensive welding techniques. ATIG offers significant cost savings and a higher production rate when compared to other welding techniques. ATIG, on the other hand, has a number of drawbacks, including high residual slag, poor mechanical properties, and low corrosion resistance. As a result, more research is needed into ATIG weld parameter optimization, ATIG process simulation, and post-weld heat treatment to address the aforementioned issues. In light of the foregoing, the focus of this study will be on ATIG welded sample experimental research, modeling, optimization, and corrosion behavior. Furthermore, the study will consider the significant difficulties associated with metallurgical properties, such as detrimental secondary phase formation, carbon migration, hot cracking, weld distortion, and residual stresses that must be removed or reduced for the weld to be qualified.

Advanced High-Strength Steels for Automotive Applications: Arc and Laser Welding Process, Properties, and Challenges

Abstract: In recent years, the demand for advanced high-strength steel (AHSS) has increased to improve the durability and service life of steel structures. The development of these steels involves innovative processing technologies and steel alloy design concepts. Joining these steels is predominantly conducted by following fusion welding techniques, such as gas metal arc welding, tungsten inert gas welding, and laser welding. These fusion welding techniques often lead to a loss of mechanical properties due to the weld thermal cycles in the heat-affected zone (HAZ) and the deposited filler wire chemistry. This review paper elucidates the current studies on the state-of-the-art of weldability on AHSS, with ultimate strength levels above 800 MPa. The effects of alloy designs on the HAZ softening, microstructure evolution, and the mechanical properties of the weld joints corresponding to different welding techniques and filler wire chemistry are discussed. More specifically, the fusion welding techniques used for the welding of AHSS were summarized. This review article gives an insight into the issues while selecting a particular fusion welding technique for the welding of AHSS.

Effect of V Content and Heat Input on HAZ Softening of Deep-Sea Pipeline Steel

Abstract: In this paper, the welding thermal cycle process of deep-sea pipeline steel was investigated by welding thermal simulation. The microstructure evolution, crystallology and second-phase precipitation behavior of the soft zone of the heat-affected zone (HAZ) were characterized and analyzed by combining scanning electron microscopy, electron back-scattered diffraction, transmission electron microscopy and hardness testing. The results show that HAZ softening appeared in the fine-grained zone with a peak temperature of 900–1000 °C for deep-sea pipeline steel, the base metal microstructure of which was the polygonal ferrite and acicular ferrite. Using V microalloying and low welding heat input could effectively decrease the softening of the HAZ fine-grained region, which was achieved by reducing the effective grain size, increasing the proportion of the dislocation substructures, and precipitating the nanoscale second-phase particles.

Effect of Ce on microstructures, carbides and mechanical properties in simulated coarse-grained heat-affected zone of 800-MPa high-strength low-alloy steel

Abstract: The application of oxide metallurgy technology to induce the formation of acicular ferrite in coarse-grained heat-affected zone (CGHAZ) to improve the welding performance of steel is a research hotspot in recent years. However, the enhancement mechanism of mechanical properties after Ce addition and the behavior of microstructures in CGHAZ of 800-MPa high-strength low-alloy (HSLA) steel are rarely reported. In the present study, the effect of Ce addition on the welding performance of 800-MPa HSLA steel was investigated by analyzing the microstructures, carbides and mechanical properties in the simulated CGHAZ. The results indicated that after the welding thermal cycle, the decrease in toughness in the CGHAZ was mainly caused by the significant decrease in the crack propagation energy. Compared to the Ce-free steel, Ce addition improved the toughness of the base metal and CGHAZ by increasing the crack propagation energy. With the same heat input, the CGHAZ strength of the Ce-containing steel was higher than that of the Ce-free steel. During the welding thermal cycle, the Nb and Ti carbonitrides greatly affected the grain growth in the CGHAZ. Ce addition significantly refined these carbonitrides, providing a stronger pinning pressure to inhibit austenite grain growth in the CGHAZ. Ce addition also refined the austenite grains and increased the proportion of high-angle boundaries in the CGHAZ, increasing the impact absorb energy and decreasing the strength loss of the CGHAZ, essentially improving the welding performance of the HSLA steel. These results are helpful for clarify the mechanism by which Ce improved the welding performance of the 800-MPa HSLA steel.

On the Influence of Linear Energy/Heat Input Coefficient on Hardness and Weld Bead Geometry in Chromium-Rich Stringer GMAW Coatings

Abstract: Wear of the working surfaces of machinery parts is a phenomenon that cannot be fully countered, only postponed. Among surface lifecycle elongation techniques, hardfacing is one which is most often used in heavy load applications. Hardfaced coating can be applied using different welding approaches or thermal spraying technologies, which differ when it comes to weld bead dimensional precision, layer thickness, process efficiency and material. In this study the authors examine the geometrical behavior and hardness properties of two distinctive chromium-based Gas Metal Arc Welding (GMAW) cored wires. The stringer beads are applied numerically with five levels of linear energy, being a resultant of typical values of welding speed and wire feed, ranging between 250 mm/s to 1250 mm/s (welding speed) and 2 m/min to 10 m/min (wire feed). The samples were cut, etched and measured using a digital microscope and Vickers indenter, additionally the chemical composition was also examined. Hardness was measured at five points in each cutout, giving 40 measurements per sample. The values were analyzed using an ANOVA test as a statistical background in order to emphasize the divergent behavior of the cored wires. It appeared that, despite having less chromium in its chemical composition, wire DO*351 exhibits higher hardness values; however, DO*332 tends to have a more stable geometry across all of the heat input levels.

Induction Heating in Underwater Wet Welding—Thermal Input, Microstructure and Diffusible Hydrogen Content

Abstract: Hydrogen-assisted cracking is a major challenge in underwater wet welding of high-strength steels with a carbon equivalent larger than 0.4 wt%. In dry welding processes, post-weld heat treatment can reduce the hardness in the heat-affected zone while simultaneously lowering the diffusible hydrogen concentration in the weldment. However, common heat treatments known from atmospheric welding under dry conditions are non-applicable in the wet environment. Induction heating could make a difference since the heat is generated directly in the workpiece. In the present study, the thermal input by using a commercial induction heating system under water was characterized first. Then, the effect of an additional induction heating was examined with respect to the resulting microstructure of weldments on structural steels with different strength and composition. Moreover, the diffusible hydrogen content in weld metal was analyzed by the carrier gas hot extraction method. Post-weld induction heating could reduce the diffusible hydrogen content by −34% in 30 m simulated water depth.

Defect formation, microstructure evolution, and mechanical properties of bobbin tool friction–stir welded 2219-T8 alloy

Abstract: Bobbin tool friction stir welding (BT–FSW) is a novel and effective welding method for aluminum alloys, but microvoid defects are usually formed in the nugget zones (NZ). Therefore, it is important to understand the formation mechanism of microvoid defects and their effect on the fracture behavior of joints. In the present study, 6 mm thick 2219–T8 aluminum alloy plates were subjected to BT–FSW under a constant rotation rate of 300 rpm and welding speeds of 150–500 mm min–1 with the objective of analyzing the evolution of microvoid defects and their effect. The results showed that, lower welding speeds resulted in microvoid defects in the band pattern structure on the retreating side (RS) of the NZ, and the size of the defects decreased with increasing the welding speed, while sound joints were obtained under higher welding speeds. In contrast to conventional FSW precipitation–hardened aluminum alloys with the lowest hardness zone (LHZ) at the heat affected zone (HAZ), the LHZs of the BT–FSW 2219–T8 joints were located at the thermal–mechanically affected zone (TMAZ). Digital image correlation (DIC) of large tensile samples showed that the microvoid defects exhibited an obvious effect on the tensile deformation and fracture behavior of the joints due to the decrease in the maximum strain and lack of necking. Mini-samples in different layers further confirmed that cracks initiated from the microvoid defects in the NZ. However, the sound BT–FSW 2219–T8 joints fractured along the LHZs on the RS, with a maximum joint strength coefficient of 78.1% being achieved.