Corrosion Resistance Of Welded Joints Research Articles

Development of a Model to Support the Management of the Resistance Welding Process

The work was carried out as part of a project to improve the corrosion resistance of welded joints. The optimal selection of input parameters reduces the consumption of welded material as well as the negative impact on the environment. The samples were welded by electrical resistance welding, more precisely by cross-wire welding. Electric resistance welding is a process for welding with electricity in which of high electrical resistance is used to generate heat at the contact point of the welded parts. Steel wire S235 with a diameter of 4 and 3 mm was used. The article shows the creation of the model to predict the percentage of setdown and weld strength as a function of the input parameters, welding current and welding time. The first task was to create a Design of experiments in which the process parameters or the range of input parameters are determined. The Design of the experiments was created for both wire diameters. This covers the range of parameters with which a welded joint of wires can be realised. A statistical analysis of the process follows, where it was found that for 4 and 3 mm diameter wires the percentage setdown increases with increasing welding current and time. An increase in strength as a function of welding current and welding time is also observed, but the results overlap in most cases and the range of their values is greater than that of setdown. The appearance of the weld was analysed for each sample. The visual inspection revealed seven categories of welds, which were divided into two groups, i.e. good and poor welds. All results were listed in a table with the percentage of expectation for a particular category of weld appearance. Based on the analysis, a model for determining the welding result parameters depending on the specified input parameters was developed, which can be used in practise to support the management of the electric resistance welding process.

Effect of post-weld heat treatment on corrosion resistance of X90 pipeline steel joints

Abstract In order to improve the corrosion resistance of welded joints, X90 pipeline steel joints were subjected to post-weld heat treatment at 610 °C, 640 °C, and 670 °C (holding time was 1 h). Through electrochemical corrosion and full immersion corrosion experiments, the corrosion resistance of welded joints under various conditions was tested, and the surface morphology and corrosion products of the corroded samples were analyzed by scanning electron microscopy and X-ray diffraction analysis. The experimental results show that the corrosion products of X90 pipeline steel welded joints in simulated soil solution mainly include Fe(OH)3, γ-FeOOH, α-Fe2O3, γ-Fe2O3, and a small amount of Fe3O4, FeCl3 and Fe. After heat treatment at 610 °C, the corrosion current density of the parent metal, heat-affected zone, and weld metal of the joint changes from 1.081, 2.889, 2.079 (×10−5 A cm−2) to 0.977, 2.211, 1.810 (×10−5 A cm−2), respectively, the corrosion resistance is improved.

Effect of Tungsten Inert Gas Remelting on Microstructure and Corrosion Resistance of Q450NQR1 High-Strength Weathering Steel-Welded Joints.

In this paper, the corrosion environment of a railway coal truck was simulated with 1.0%H2SO4 + 3%NaCl solution. The effect of weld toe Tungsten Inert Gas (TIG) remelting on the microstructure and corrosion resistance of welded joints of Q450NQR1 high-strength weathering steel was studied. The results show that the weld toe melts to form a remelting area after TIG remelting. After TIG remelting, the weld geometry was improved, and the stress concentration factor decreased from 1.17 to 1.06 at the weld toe, a decrease of 9.4%. TIG remelting refines the microstructure of the weld toe and improves the corrosion resistance of the welded joint. The surface of the TIG-remelted sample is uniformly corroded with no "deep and narrow" pits after the removal of corrosion products. The weight loss rate and corrosion rate of remelted welds are lower than those of unremelted welds. The structure of corrosion products is loose at the initial stage of corrosion, and the corrosion products are transformed into Fe3O4 and Fe2O3 protective rust layers with a dense structure after 480 h of corrosion. With the extension of corrosion time, the tensile strength and percentage elongation of the specimen decreased linearly. The decreasing rates of tensile strength of remelted and unremelted specimens were 0.09 and 0.11, respectively, and the decreasing rates of elongation after fracture were 0.0061 and 0.0076, respectively.

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.

Исследование свариваемости полуфабрикатов из сплава системы Al – Mg – Si – Cu

The features of the formation of the microstructure of welded joints of sheets of aluminum alloy V-1381 of the Al – Mg – Si – Cu system, obtained with various parameters of automatic argon-arc welding, were studied. Welding modes were selected that provide a high-quality welded joint and strength at a level not lower than 0.8 of the strength of the base metal. It has been established that welding without filler wire leads to cracking without applying tensile deformation, the use of Sv1221 filler wire compared to SvAMg61 and SvAK5 leads to an increase in the strength characteristics of welded joints by 15 – 20 %. Corrosion resistance of welded joints of sheets from V-1381 alloy was determined. Various experimental modes of laser welding were tested, the microstructure and mechanical properties of welded joints were studied. Parameters have been selected that ensure high quality of welds. The possibility of using laser welding for semi-finished products from alloy V-1381 has been established. The new V-1381 alloy can be recommended for use in aircraft fuselage structural elements, including as an alternative to less corrosion-resistant non-weldable alloys of the D16 type, which will increase the weight efficiency of structures both due to increased strength and through the use of welded joints instead of riveted ones.

Microstructure, mechanical properties and corrosion resistance of friction stir welded joint of Al–Mg–Mn–Zr–Er alloy

Abstract The microstructure, mechanical properties and corrosion resistance of friction stir welded joint of Al–Mg–Mn–Zr–Er alloy were investigated under three FSW parameter sets: 800 rpm × 100 mm min−1, 800 rpm × 80 mm min−1 and 600 rpm × 80 mm min−1. The microstructural transformation sequence of welded joint is discontinuous dynamic recrystallization, dislocation introduction, dynamic recovery and continuous dynamic recrystallization. The mechanical properties of welded joint are highly correlated with the welding process parameters. The welded joint can obtain good tensile strength and elongation under the parameters of 800 rpm × 100 mm min−1. Corrosion resistance of welded joints has little correlation with welding parameters, but is mainly related to different positions of welded joints. The main influencing factor is grain structure state. The intergranular corrosion susceptibility is related to β(Al3Mg2) phase.

Potentiodynamic Corrosion Behavior and Microstructural Characteristics of Pulsed CMT-Welded AA2014-T6 Aluminium Alloy Joints: Effect of PWHT

AA2014-T6 is an Al-Cu-Mg-based precipitation-hardened aluminium alloy widely used in aerospace due to its high strength to weight ratio. This alloy is joined by a pulsed cold metal transfer (PCMT) arc welding process to overcome the high heat input related problems in gas metal arc welding (GMAW) such as a coarser dendritic structure in the fusion zone (FZ), wider heat affected zone (HAZ), solidification and HAZ liquation cracking, softening in HAZ, and poor corrosion resistance of welded joints in salt environment. The joints were subjected to PWHT of artificial aging (AA), solution treatment (ST), and solution treatment + aging (STA) conditions. The corrosion rate was determined using a potentiodynamic corrosion test in a solution of 3.56 wt.% NaCl with pH values of 4, 7, and 11. Results disclosed that the PCMT joints subjected to the potentiodynamic corrosion test in NaCl solution of pH-4, pH-7, and pH-11 disclosed very low, moderate, and extremely high pitting corrosion, respectively. The corrosion resistance of ST joints was improved by 53.34%, 15%, and 15.12% in pH-4, pH-7, and pH-11 NaCl solution compared to as-welded joints. The pitting potential of ST joints is comparable to BM. The BM showed the pitting potential of −175, −450, and −550 mV in pH-4, pH-7, and pH-11 NaCl solution. The ST joints showed 75.29%, 29.16%, and 27.85% lower corrosion potential compared to STA joints in pH-4, pH-7, and pH-11 NaCl solution, respectively. The ST joints disclosed the lower pitting potential of −105, −425, and −505 mV in pH-4, pH-7, and pH-11 NaCl solution, respectively, whereas the STA joints revealed greater pitting potential of −425, −600, and −700 mV in pH-4, pH-7, and pH-11 NaCl solution, respectively. The superior corrosion resistance of ST joints compared to AA and STA joints is attributed to the dissolution of precipitates in Al solid solution resulting in a lower potential difference in FZ. This minimizes the preferential sites for pitting corrosion to occur.

Effect of Heat Input on Microstructure and Corrosion Resistance of CP-Ti Laser Beam Welded Joints

The TA1 welded joints with different heat inputs were obtained by a fiber laser and their microstructure, mechanical properties and corrosion resistance in simulated saliva solution were studied. The results show that the microstructure in fusion zone (FZ) is needle-like α′ martensite and lath-shape α′ martensite, and that of the heat-affected zone (HAZ) is zigzag α phase. With the increase of heat input, the volume fraction of needle-like α′ martensite decrease and the microstructure is coarsened in FZ, but there is almost no change in the microstructure of the HAZ. The order of the corrosion resistance of welded joints with different heat inputs is the same as FZ > HAZ > base material (BM), and the heat input has a more influence on the corrosion resistance of FZ. The binary multiple linear regression relationship between the corrosion current density/charge transfer resistance and the length/width of α′ martensite was established, indicating that the width of α′ martensite is the main factor affecting the corrosion resistance.

Study of joint microstructural properties of ZrC/Al-Mg composites-enhanced AA7075

ABSTRACT In this study, the ZrCp/Al-Mg composite fillers, successfully prepared using semi-solid stir casting, ultrasonic vibration and multi-pass rolling processes, were joined with 7075-T651 plates via tungsten insert gas (TIG) welding. The metallographic structure, tensile strength, microhardness and corrosion resistance were investigated. The results indicated that the introduction of ZrC particles favoured the continuous heterogeneous nucleation and inhibit the formation of coarse precipitates in the composite materials. The uniform distribution of ZrC particles could refine α-Al grains. As a result, the mechanical properties and corrosion resistance of weld joints were improved compared to those with 5183 fillers. Study turned out the optimal amount of ZrC particles was 2 wt.%, improving significantly on grain size, tensile strength, corrosion resistance and microhardness.

Multiscale characterization of seawater pipe erosion of B10 copper\u2013nickel alloy welded joints

In seawater pipeline, the welding joint is a non-uniform structure composed of welding seam, base metal and heat affected zone. It has inhomogeneity in chemical composition, organizational structure, residual stress, etc. As local defects and high turbulence accelerate corrosion, the welding joint is often the weakest link in pipeline corrosion. Herein, the electrochemical corrosion behavior of B10 alloy welded joint in flowing seawater is studied from macroscopic and submicroscopic viewpoints using AC impedance, linear polarization, array electrode and morphological characterization. The results reveal that the corrosion rate of weld metal (WM), base metal (BM) and heat-affected zone (HAZ) decreased with the increase of time. Combined with SEM and EDS analysis, it can be seen that the increase in time led to the decomposition and accumulation of corrosion products, which gradually enhanced the corrosion resistance of welded joints. At the submicroscopic scale, WM acts as a cathode to mitigate corrosion during the later stages of high flow rate.

Studying the effect of heat treatment modes on corrosion resistance of welded joints

Studying the effect of heat treatment modes on corrosion resistance of welded joints

Corrosion resistance of welded joints made by underwater wet welding

One of the reasons of coming out of order of metal structures, operating in water environment, including sea conditions, is the corrosion. Thus, for example, the corrosion wear of metal of the ship hull underwater part can reach from 0.3 up to 0.5 mm/year. The corrosion of welds is the ever more critical situation. The rate of their fracture exceeds the rate of the base metal corrosion and in some cases it may reach 1-3 mm/year [1, 2]. The great selective corrosion in the form of fissures along the welds (on both sides) was observed in heat-affected zone (HAZ) metal of slot, butt welds and welds for welding-on to the basic workpiece, i.e. up to 1 mm/year, in some cases a through corrosion fracture of the fusion line (formation of blowholes) was observed [1]. In the opinion of the work authors [2] the welds are subjected to fracture due to the occurrence of thermal electromotive force between the parts welded under conditions of high electric conductivity of the sea water (Seebeck effect).
 To repair the corroded welded joints of metal structures, operated under the water, a wet underwater welding is used. At the E.O.Paton Electric Welding Institute the specialized flux-cored wires have been developed, which are designed for welding low-carbon and low-alloyed steels, including those of a higher strength. In the latter case the electrode materials of an austenite type are used to provide resistance against cold crack formation in the HAZ [3]. The work was aimed at study of corrosion resistance of welded joints with ferrite and austenite deposited metal, made by the underwater wet welding, under the conditions, which simulate the service conditions in sea water.

CHARACTERIZATION OF CHROMIUM NITRIDE PRECIPITATION IN THE HEAT AFFECTED ZONE OF THE SUPERDUPLEX STAINLESS STEEL UNS S32750: AN EXPERIMENTAL AND NUMERICAL ANALYSIS

It is well known that pitting corrosion resistance of duplex and superduplex stainless steels strongly depends on 
 microstructural characteristics such as ferrite/austenite proportion, presence of intermetallic phases and elemental partitioning between the austenite and ferrite phases. In particular, during the welding operation, very fine chromium nitrides may precipitate 
 within ferrite grains of the heat affected zone drastically reducing the corrosion resistance of welded joints of duplex and super duplex stainless steels. However, due to their small size and low distribution, analyzing the chemical composition and crystallography of chromium nitrides is quite difficult and only a restricted number of advanced techniques of investigation may discriminate their signal from the surrounding matrix. This work is aimed at supporting the microstructural characterization of a welded joint of a superduplex stainless steel by means of a field-emission gun scanning electron microscope. Sub-micron chromium nitride precipitates, identified within the ferritic grains of the heat affected zone, are recognized to be the main reason for the reduced pitting corrosion resistance of the analyzed welded joints. The results are supported by a multi-pass welding process numerical simulation aimed at estimating the cooling rates promoting chromium nitride precipitation in the heat affected zone.

Influence of Shielding Gas on Microstructure and Properties of GMAW DSS2205 Welded Joints

In the present study, the microstructures and properties of DSS 2205 solid wire MIG welded samples prepared in different shielding gases (pure Ar gas, 98%Ar + 2%O2 and 98%Ar + 2%N2) were investigated for improving the weldability of DSS 2205 welded joint. The work was conducted by mechanical property tests (hardness and tensile test) and corrosion resistance property tests (immersion and electrochemical tests). The results show that adding 2%O2 into pure Ar gas as the shielding gas decreases crystal defects (faults) and improves the mechanical properties and corrosion resistance of the welded joints. Phase equilibrium and microstructural homogeneity in welded seam (WS) and heat-affected zone (HAZ) can be adjusted and the strength and corrosion resistance of welded joints increased obviously by adding 2%N2 to pure Ar gas as the shielding gas. Compared with DSS 2205 solid wire MIG welding in 98%Ar + 2%O2 mixed atmosphere, the strength and corrosion resistance of welded joints are improved more obviously in 98%Ar + 2%N2 mixed atmosphere.

Effect of heat treatment on the corrosion resistance of welded joints from austenitic steel obtained using laser radiation*

ABSTRACT The influence of heat treatment of a welded joint from austenitic steel 12Cr18Ni10Ti on the microstructure and resistance to intergranular corrosion, which was determined according to GOST 6032–2003 (AMU method), was evaluated. It was found that heat treatment according to the two modes used has an effect on the microstructure. After testing for intergranular corrosion and three-point bending cracks or damage in the welds with heat treatment is not observed. The seams are highly resistant to intergranular corrosion. The weld seams without heat treatment also did not have intergranular damages due to a slight dissolution of titanium carbides in austenite and the absence of chromium carbides along the grain boundaries.

Effects of nitrogen element on microstructure and pitting corrosion resistance of duplex stainless steel welded joints

The microstructure, element distribution and pitting corrosion resistance of Gas Tungsten arc welding (GTAW) duplex stainless steel welded joints under 100% argon (Ar) and 98% Ar + 2% nitrogen (N2) shielding gas were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrochemical corrosion methods. These results show that the addition of N2 to the shielding gas promotes the formation of austenite (γ) phase in the weld joint. Also, the austenite phase distribution is dendritic and the ferrite (δ) and austenite phases in the heat-affected zone are no longer banded structures. Moreover, the austenite phase in the welded joint is enriched in nickel (Ni) and nitrogen (N) elements, while the ferrite phase is enriched in chromium (Cr) and molybdenum (Mo) elements. The pitting corrosion index (PREN) of the austenite/ferrite (δ/α) phase boundary is lower than that of δ and γ phases, which leads to their preferential corrosion. The appearance of chromium nitride (Cr2N) decreases the corrosion resistance of the weld seam and the heat affected zone. N2 in the 98% Ar + 2% N2 shielding gas can restrain Cr2N precipitation, increase the pitting corrosion index of secondary austenite structure (γ 2), and improve the pitting corrosion resistance of welded joints.

Studying Corrosion Resistance of Weld Joints of Ultrafine-Grained Titanium Alloys

Ultrafine-grained (UFG) samples of PT-3V near-α titanium alloy were subjected to diffusion welding using the Spark Plasma Sintering system. It has been shown that the destruction of welded UFG samples under hot salt corrosion (HSC) is two-staged – first, intercrystalline corrosion is manifested, which then graduates to pitting corrosion. It has been established that the corrosion resistance of weld joints is determined by vanadium concentration at the grain boundaries, the size and volume ratio of β-phase particles and the presence of pores in the weld joints. It has been shown that welded UFG samples possess higher hardness and corrosion resistance than coarse-grained samples.

Impacts of Stress Relief Treatments on Microstructure, Mechanical and Corrosion Properties of Metal Active-Gas Welding Joint of 2205 Duplex Stainless Steel.

Stress relief treatments were carried out separately with a pneumatic chipping hammer, ultrasonic peening treatment, and heat treatment for metal active-gas welding (MAG) welded joints of 2205 duplex stainless steel. The effects of these methods on the residual stress, microstructure, mechanical properties and corrosion resistance of welded joints were studied. Results show the stress state of the weld and the surrounding area was effectively improved by the pneumatic chipping hammer and ultrasonic peening treatment, and the residual stress field of the surface layer changed from tensile stress to compressive stress. On the contrary, low-temperature stress relieving annealing had no obvious effect on stress distribution. After the pneumatic chipping hammer and ultrasonic peening treatment, the welded joints were machined and hardened. Correspondingly, strength and hardness were improved. However, the heat treatment only led to a slight decrease in strength and hardness due to the static recovery of the welded joint structure. All stress relief methods effectively improved the corrosion resistance of welded joints, with the ultrasonic peening treatment giving the best performance.

Influence of Surface Ultrasonic Rolling on Microstructure and Corrosion Property of T4003 Ferritic Stainless Steel Welded Joint

In this paper, the effect of surface ultrasonic rolling treatment (SURT) on surface properties of T4003 cold metal transfer (CMT) welded joints was studied. Surface topography and microstructure changes of the welded joint surface before and after SURT were observed by optical microscope and scanning electron microscope. The hardness and residual stress distribution of welded joint were measured by a microhardness tester and X-ray diffractometer. The change of corrosion resistance of welded joints was studied by electrochemical polarization curve measurement. The results show that surface roughness (Ra) of the weld zone, heat affect zone (HAZ), and base metal after SURT was reduced to 0.320 μm, 0.156 μm, and 0.227 μm, respectively, and surface morphology became smooth. The plastic deformation layer and working hardening layer were formed at the welded joint. The degree of plastic deformation of the weld zone was more serious than that in the base metal, and grains in weld zone was obviously refined. The thickness of plastic deformation layer was about 100 μm. The surface hardness in the weld zone was highest, which is about 420 HV. The refinement of grains and the increase of surface hardness can improve the fatigue life of welded joint. After SURT, the residual stress in the welded joint changes from residual tensile stress to residual compressive stress, which can also improve fatigue life of the welded joint. Surface corrosion resistance of welded joints after SURT was improved due to smooth surface and the formation of fine grains layer.

ВПЛИВ ТЕМПЕРАТУРИ ТЕРМІЧНОЇ ОБРОБКИ НА СТІЙКІСТЬ ДО МІЖКРИСТАЛІТНОЇ КОРОЗІЇ ЗВАРНИХ З'ЄДНАНЬ

Welded joints with corrosion-resistant steels and heat-resistant alloys requiring different modes of heat treatment to achieve the level of mechanical properties specified in the design documentation are used to manufacture parts and components of the rocket engine turbo-pump unit.For the manufacture of parts and assemblies of liquid-propellant rocket engines at the machine-building enterprises of Ukraine there was a necessity of replacement of half-finished products because of certain difficulties at delivery of materials from EU countries.First of all, it was necessary to replace flat products from high-alloy ХН67МВТЮ and 06Х15Н6МВФБ with one alloy that would possess the necessary set of physicomechanical characteristics. In the work, as a replacement for the used heat-resistant alloys, the Inconel 718 alloy welded to 316L steel was chosen. As a result of comparative studies of the intercrystalline corrosion resistance of welded joints of the heat-resistant Inconel 718 alloy with stainless steel, after testing various heat treatment conditions, the low-temperature heating conditions were recommended for soldering at a temperature of 950°C. Samples of welded joints, processed according to the recommended mode, showed increased corrosion resistance.