Weld Fusion Zone Research Articles

Laser beam weldability of TiZrHfNbTa high entropy alloy and dissimilar weldability to C103 refractory alloy

Weldability is one of the most important processes for new metallic alloys moving toward engineering applications. In this work, both the laser beam weldability of an equiatomic TiZrHfNbTa refractory high entropy alloy (HEA) and the dissimilar weldability of TiZrHfNbTa to C103 niobium-based alloy are assessed. Single BCC phase maintains stability around both the TiZrHfNbTa welding joint and HEA-C103 dissimilar welding joint. Fine equiaxed grains are obtained within these two types of weld fusion zones with no detectable macro- or microcracks formation. Despite the existence of a small amount of porosity in the fusion zone, the tensile properties of samples containing welding joints are comparable to the corresponding base materials. This work confirms the prototype TiZrHfNbTa refractory HEA has excellent laser weldability and meanwhile exhibits good dissimilar weldability to widely used C103 alloy.

Electromagnetic (EM) sensor measurement for residual stress characterisation in welded steel plates

ABSTRACT Residual stresses can cause compromise in structural integrity; it is desirable to assess residual stresses using non-destructive testing so that effects on structural properties can be predicted. Electromagnetic (EM) sensors can be used to characterise residual stresses in steels accounting for, microstructure and geometry effects. Residual stress characterisation in welded EN S275 steel plates using EM sensors is reported. Low-frequency, low-magnetic field EM sensors were used to assess residual stresses in the plates. A finite element model for the sensor and sample was generated in COMSOL software so the influence of weld bead geometry and microstructure could be predicted and accounted for. This allowed residual stresses to be determined from EM sensor measurements, excluding the geometry and microstructure effects, XRD was used to verify EM sensor measurements. The highest residual stresses were found adjacent to the weld fusion zone, with magnitudes of, 170±5MPa, 120±20MPa and 42±10MPa for X-ray diffraction (XRD), a small EM sensor (U-12.7) and a big EM sensor (U-31) types, respectively. The differences are due to the volume of the material measured by each measurement type. It was shown that EM sensors are capable of measuring residual stress in welded plates to a good level of accuracy.

3D characterization of internal defects for fatigue performance of welded SA192 steel water walls

Weld defects in SA192 steel water walls have been characterized using 3D nano-tomography. The fatigue test specimens were extracted from different weld locations of the water walls. The internal welding defects number, size, shape, and location were measured before low-cycle fatigue tests. The weld defect size and shape were found to be the most prominent factors influencing fatigue crack initiation and fatigue life. Sharper defects significantly reduce the fatigue life of the specimen as compared to the rounder defects. The stress intensity factor for each type of defects was calculated using linear-elastic fracture mechanics and the Murakami methods. In the defect-free specimens, the weld fusion zone was the most preferential sites for fatigue crack initiation due to a higher hardness of the as-solidified microstructure.

Microstructural modelling and characterisation of laser-keyhole welded Eurofer 97

The novel reduced activation ferritic/martensitic steel Eurofer 97 is employed by many concept designs for the plasma-facing first wall of the EU DEMO fusion reactor. These designs feature precision joints between Eurofer 97 coolant piping, for which an advanced laser-keyhole welding technique is proposed. In this work the microstructure of these novel laser-keyhole Eurofer 97 welds is modelled by combining finite element thermal analysis with precipitate kinetics modelling. Microanalysis of a representative specimen via scanning electron and high-speed atomic force microscopy techniques is also conducted, complimented by electron backscatter diffraction, energy-dispersive X-ray spectroscopy, and nanoindentation hardness testing. Models of the weld microstructure agree well with the results of microanalysis although the precipitate diameters predicted are slightly underestimated. Several large void defects were discovered within the weld fusion zone, the cause of which is suspected to arise from the evaporation of cerium-rich oxide inclusions present in the as-cast Eurofer 97 during welding.

Corrosion Resistance of Dissimilar GTA Welds for Offshore Applications

The pitting corrosion resistance of dissimilar pipeline steel API X70 and Super Duplex 2507 Stainless Steel gas tungsten arc (GTA) welds was studied. The GTA welds were fabricated using Super Duplex 2594 Filler Metal or austenitic 309L Filler Metal. The specimens extracted from the base metal, weld fusion zone, fusion boundary, and heat-affected zones (HAZs) were subjected to a potentiodynamic corrosion test in a 3.5% NaCl water solution. The weld made using the 309L Filler Metal was found to have a smaller pitting resistance equivalent number (PREN) difference between ferrite and austenite, making it more corrosion resistant than the weld fabricated using the 2594 Filler Metal. The HAZ on the X70 side was the most susceptible to pitting and galvanic corrosion for both filler metals.

Investigating the mechanical properties and fusion zone microstructure of dissimilar laser weld joint of duplex 2205 stainless steel and A516 carbon steel

Laser welding of dissimilar A516 low carbon steel and duplex stainless steel was conducted to evaluate the effect of fiber laser welding parameters (e.g., laser power, welding speed, nozzle distance and beam deviation) on the responses of tensile strength, depth of the melt pool, microstructure, temperature near the melt pool and melt pool hardness. The maximum tensile strength of 500 MPa and 18 percent elongation were obtained at the laser power of 400 W, welding speed of 300 mm/min and the focal point. The absorbed power of laser and linear speed of welding had the most notable impact on the tensile strength of the weld. The fusion zone microstructure was composed of a combination of ferrite–austenite distribution from duplex stainless steel (DSS) based on different cooling and heating cycles. During the nucleation process, ferrite grains were transformed to austenite grains from different areas of the fusion zone. Also, the weld fusion zone microstructure at A516 side was composed of fully martensitic structure, according to the higher heat input upper critical temperature of steel (AC3), thereby leading to rapid cooling. The EDS analysis also showed that the Fe percentage was continually reduced at the fusion line from A516 to DSS, although Ni and Cr were distributed at the fusion zone with some minor changes of weight percentage. Therefore, Cr and Ni had a crucial effect on elemental alloy composition in this laser welding process. The ductility of the A516 fracture surface with bigger and deeper fracture dimples was caused by applying higher laser energy density, which effectively improved the fracture ductility of the welded samples.

In-Depth Characterization of Laser-Welded Aluminum-and-Copper Dissimilar Joint for Electric Vehicle Battery Connections.

With advancements in the automotive industry, the demand for electric vehicles (EVs) has remarkably increased in recent years. However, the EV battery, which is a vital part of the EV, poses certain challenges that limit the performance of the EVs. The joining of dissimilar materials for different components affects the electrical and mechanical performances of EV batteries. Laser beam welding is a promising technique for joining Al and Cu for application in secondary battery fabrication because of the precise control over heat input and high process speed. However, the production of Al-Cu joints remains challenging because of the differences between their thermal and metallurgical properties and the resulting formation of brittle and hard intermetallic compounds, which reduce mechanical and electric properties. Thus, it is vital to characterize the weld to improve joint performance and enhance the laser welding process. This study investigates the joining of an Al alloy (AA1050) with Ni-coated Cu using a continuous-wave Yb fiber laser. The evaluation of the weld morphology showed a correlation between the weld characteristics and process parameters (laser power and welding speed). The weld interface width and penetration depth into the lower sheet (Cu) both increased with increasing heat input. Optical microscopy of the weld cross-section revealed many defects, such as voids and cracks. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) was employed to examine the weld microstructure. The composition analysis revealed the presence of mixed morphology of Al-Cu eutectic alloy (α-Al+Θ-Al2Cu) phase in the form of dendrites in the weld fusion zone with traces of the highly brittle Al4Cu9 phase at a high heat input condition. Furthermore, the electrical contact resistance of the weld seam was measured to determine the correlation between heat input and resistance. In addition, Vickers microhardness measurements were performed on the weld cross-section to validate the SEM/EDS results.

Failure analysis of weld cracking of gas gathering pipeline in dewatering station

There are a lot of welded joints in the shale gas collection pipeline, so the failure risk of the shale gas production line is very high. A leak has occurred in the gas collection pipeline of a dewatering station, and in order to find out the causes of failure and provide technical support for safe shale gas transmission, macroscopic analysis, non-destructive testing (X-ray flaw detection), mechanical properties, and metallurgical analysis were performed on the failed pipe section, and CFD method was used to further analyze the failure mechanism of the ring weld pipe. The macroscopic analysis yielded the weld height is significantly greater than the standard minimum requirement. Non-destructive testing showed a large number of cracks with varying degrees of extension along the weld circumference on the inner surface of the weld. The chemical composition and mechanical properties of the pipe and the weld met the requirements. The microstructure of the base metal met the standard. There are no inclusions, holes, unfused areas, or other welding defects in the weld zone. The cracks originate from the weld fusion zone, and there are a large number of intergranular microcracks. CFD simulation results show that although the stress concentration caused by the height of the weld does not directly lead to weld cracking, under the influence of the stress concentration, cracks tend to sprout at the coarse grain organization of the fusion zone on the inner surface of the weld and can easily propagate throughout the weld and pipe wall thickness, leading to crack damage. Several suggestions to prevent such a failure were proposed to avoid the occurrence of similar accidents.

Residual stress analysis, microstructural characterization, and mechanical properties of tungsten inert gas-welded P92/AISI 304L dissimilar steel joints

In the present work, the creep strength-enhanced ferritic martensitic P92 steel was welded with 304L austenitic stainless steel. The dissimilar joining of these two different grades of material was performed by using tungsten inert gas welding process. The nickel-based ERNiCr-3 welding consumable was used. The influence of post-weld heat treatment (760 °C, 2h), called as tempering, was also investigated. The secondary electron and optical image confirmed that ERNiCr-3 weld metal is accompanied by an equiaxed austenitic microstructure with Ni weight percentage of 68.29%. The energy-dispersive X-ray spectroscopy and electron probe microanalyzer results of the weld fusion zone revealed the Nb, Cr, and Ti segregation in the inter-dendritic region. The elemental mapping of the carbon-depleted zone, and the interface was performed using an electron probe microanalyzer, which revealed the diffusion of Ni, Cr, and Fe across the interface of P92 steel and ERNiCr-3 filler weld. The tensile test result indicated that part of the dissimilar weld joints (DWJs) with relatively weak ultimate tensile strength was ERNiCr-3 weld metal. The ultimate tensile strength value of the DWJs was observed as 610 MPa and 580 MPa in the as-weld and post-weld heat treatment situations, respectively. The Charpy V-notch impact energy of the ERNiCr-3 weld fusion zone was achieved as 135 ± 2 J and 140 ± 2 J in as-weld and post-weld heat treatment situations, respectively. The low impact toughness of the ERNiCr-3 weld metal was attributed to the presence of niobium carbide (NbC) and titanium carbide (TiC) particles. The peak longitudinal residual stress of 490 MPa and transverse residual stress of 442 MPa were noted in the ERNiCr-3 weld fusion zone at a depth of 3 mm from the top surface. The tempering heat treatment exhibited a significant drop in the residual stresses value for the weld fusion zone and heat affected zone (HAZ).

Refined weld microstructure and enhanced joint mechanical property of 1460 Al-Li alloys via double-pulsed variable polarity TIG arc welding

In this work, 1460 Al-Li alloy plates (thickness 2 mm) were butt-welded by using conventional variable polarity TIG welding (VPTIG), low-frequency pulsed (2 Hz) variable polarity TIG welding (P-VPTIG), and double-frequency (low-frequency (2 Hz) + ultrasonic-frequency (20 kHz)) pulsed variable polarity TIG welding (DP-VPTIG). The influences of the three current modes on the weld microstructure and mechanical properties were investigated contrastively. Weld microstructure was characterized by a metallographic optical microscope, scanning electron microscope, and electron backscattering diffraction technology. The mechanical properties of those 1460 Al-Li alloy-based joints were measured by microhardness and room-temperature uniaxial tensile test. Obtained results indicated that modulating pulsed current on the conventional VPTIG current can effectively eliminate the coarse columnar structures, resulting in whole refined equiaxed grains in the weld zone (WZ) and fusion zone (FZ). By comparison, DP-VPTIG current exhibited the most prominent effect of homogenization and refinement on the weld microstructure. In addition, it significantly increased the quantity and width of the fine strip-like equiaxed grain zone. The eutectic phase particles distributed in the grain boundaries were refined prominently by the modulation of pulsed current. Compared with the VPTIG process, both P-VPTIG and DP-VPTIG processes effectively enhanced the strength and elongation of 1460 Al-Li alloy-based joints, with an increase of 6.2 % and 10.9 % in tensile strength and 16 % and 128.6 % improvement in elongation, respectively.

Dissimilar joining of the martensitic grade P91 and Incoloy 800HT alloy for AUSC boiler application: Microstructure, mechanical properties and residual stresses

The presented study intends to analyze the microstructure and corresponding mechanical characteristics of P91 and Incoloy 800HT dissimilar welded joint (DWJ). The thermo-physical property differences between P91 and Incoloy 800HT arise due to their complex alloying composition, making their weldability difficult. Incoloy 800HT is difficult to weld due to its high susceptibility to solidification cracking. The recommended nickel-based filler metals for welding Incoloy 800HT were employed to weld P91 and Incoloy 800HT using conventional gas tungsten arc welding (GTAW). The welded joint morphology and characteristics were analyzed in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The PWHT was performed to observe changes in microstructural inhomogeneity and residual stress relaxation in weld after the heat treatment. An electron probe microanalyzer (EPMA) was utilized to observe the distribution and segregation of elements in different weld regions. The deep hole drill technique was employed to find the distribution of bi-axial residual stresses in the weld fusion zone (WFZ) and heat-affected zone (HAZ) of base metals in both AW and PWHT conditions. The two nickel-based fillers, ERNiCr-3 and ERNiCrMo-3, were employed, and their weld characteristics were compared. The mechanical strength of ERNiCr-3 filler-based DWJ was found superior to ERNiCrMo-3 filler-based DWJ. The standard AW and PWHT ERNiCr-3 filler-based DWJ tensile specimen failed from Incoloy 800HT base metal with an ultimate tensile strength (UTS) of 570 ± 4 MPa and 650 ± 4 MPa, respectively. The ERNiCrMo-3 filler-based DWJ obtained the highest UTS of 679 MPa after PWHT in a subsize specimen. The microhardness for ERNiCrMo-3 WFZ was found to be higher than ERNiCr-3 WFZ microhardness, and PWHT successfully tempered the P91 HAZ. Further, the impact toughness for the ERNiCr-3 WFZ in AW condition was 86 ± 3 J and PWHT did not provide any significant improvements, while ERNiCrMo-3 WFZ had an impact toughness of 47 ± 10 J in AW state and 41 ± 10 J in PWHT state. Thus, a successful weld characteristic study of defect-free P91 and Incoloy 800HT DWJ was completed, and ERNiCr-3 filler was concluded to be an optimum choice of filler to make the DWJ between P91 and Incoloy 800HT.

Investigation on joining P91 steel and Incoloy 800HT through gas tungsten arc welding for Advanced Ultra Super Critical (AUSC) power plants

The present study focuses on dissimilar metal weld (DMW) of P91 ferritic-martensitic steel and Incoloy 800HT. The DMW was made nickel-based filler ERNiCrCoMo-1 filler using Tungsten Inert Gas (TIG) welding. Exhaustive microstructure analysis was done for the DMW. A stable austenitic microstructure was observed in the DMW solidified weld fusion zone (WFZ). Based on the peak welding temperature exposure in the different regions, the corresponding microstructure was observed to investigate the grain size transformations, phase transformations, diffusion, and segregation of constituent solute elements. Advance microstructure analysis was performed using Electron Probe Micro Analyzer (EPMA). Further, the effect of the observed microstructure feature on the mechanical property of the DMW was studied. The developed residual stresses were relaxed by post-weld heat treatment (PWHT). The tensile strength of the DMW was recorded less than the tensile strength of base metals. Also, impact toughness in as-welded (AW) WFZ was 117 J and reduced to 102 J after PWHT. Microhardness analysis showed maximum value in P91 heat-affected zone (HAZ) due to the dissolution of precipitates. It was reduced through tempering. The DMW of P91 and Incoloy 800HT was successfully produced without any major defect and with sufficient mechanical strength to put it in consideration for use in advanced ultra-supercritical (AUSC-Generation IV) boiler pipes and tubes as per the ASTM standards.

Influence of PWHT Parameters on the Mechanical Properties and Microstructural Behavior of Multi-Pass GTAW Joints of P92 Steel.

The 9% Cr steels were developed for ultra-supercritical (USC) power plants to meet the requirements of high operating temperature and pressure. These steels are produced to operate at high temperatures where impact toughness is not a concern; however, it becomes important for the welded joints to have good impact toughness at room temperature for manufacturing. The present work investigates the effect of the post-weld heat treatment (PWHT) parameters, i.e., temperature and time, on the impact toughness of multi-pass gas tungsten arc welded (GTAW) joints of ferritic/martensitic grade P92 steel. The microstructural evolution in welded joints given varying post-weld temperatures and times was studied. The lath martensitic structure of the weld metal for the as-welded joints resulted in high hardness and low impact toughness. The weld fusion zone toughness was 12 J, which was lower than the minimum specified values of 41 J (ASME standards) and 47 J (EN ISO 3580:2017). The PWHT temperature and time were found to have a significant effect on the impact toughness of the weld metal. A drastic increase in the impact toughness of the weld metal was noticed, which was attributed to lath break-up, reduction in dislocation density and reduction in solid solution hardening. The maximum impact toughness of 124 J was measured for PWHT temperature and time of 760 °C and 120 min, respectively. The effect of PWHT parameters on tensile strength was also investigated, and test results showed that the joint was safe for USC boiler application as it failed from the region of the P92 base metal. The variation in microstructural evolution along the weldments resulted in hardness variation. PWHT led to homogeneity in microstructure and, ultimately, reduction in hardness value. According to the study, the optimum temperature and time for PWHT of a GTAW joint of P92 steel were found to be 760 °C and 120 min, respectively.

Influence of hot corrosion on pulsed current gas tungsten arc weldment of aerospace-grade 80A alloy exposed to high temperature aggressive environment

• The performance of alloy 80A weldment in a high-temperature aggressive environment was studied. • The effect of hot corrosion on different welding techniques (GTAW and PCGTAW) and filler wires (ERNiCrMo-3 and ERNiCr-3) were studied. • Influence of PCGTAW technique in protecting the surface of the welded substrate from an aggressive environment.IV) The mechanism of the formation of corrosive and protective oxides and its effect on the corrosion behaviour of welded substrates were studied. One of the significant issues that shorten the life of components used in high-temperature applications is hot corrosion. The current study compares the performance of welded aerospace-grade 80A fabricated through continuous and pulsed gas tungsten arc welding techniques. Weld coupons are produced using two different filler wires (ERNiCrMo-3 (Mo-3) and ERNiCr-3 (Cr-3)). Welded substrates are subjected to 50 cycles of air oxidation and Na 2 SO 4 + 60%V 2 O 5 molten salt environmental conditions at 900 °C. Corrosion products were analysed through scanning electron microscope/energy dispersive spectroscopy and X-ray diffraction analyses. Thermogravimetric analysis revealed that all welded substrates trailed the parabolic rate of law kinetics. In the molten salt (MS) environment, gas tungsten arc welded (GTAW) Mo-3 substrate showed more weight gain. In contrast, a minor weight gain was observed in the pulsed current gas tungsten arc welded (PCGTAW) Cr-3 substrate. It indicates that accelerated corrosion kinetics was observed in the molten salt environmental condition that showed more weight gain than air oxidation. amongst the weldments, pulsed current gas tungsten witnessed superior corrosion-resistant behaviour. This phenomenon is observed due to grain refinement suppression of heat-affected zones and secondary phases in the weld fusion zone. In addition, the appearance of protective oxides such as Cr 2 O 3 , NbO and NiCr 2 O 4 helps arrest the oxidation at the surface and sub-surface layer by providing good resistance against hot corrosion to the welded substrate. Thus, utilizing the PCGTAW technique during the fabrication/refurbishing process helps promote the material's corrosion resistance against a hot corrosion environment.

Characterization of Microstructure, Weld Heat Input, and Mechanical Properties of Mg–Al–Zn Alloy GTA Weldments

The present study investigated the influence of welding speed on the microstructure, hardness, and tensile properties of the AZ31 Mg alloy gas tungsten arc (GTA) welds that were prepared using alternating current (AC). A microstructural examination of the weld metal and base metal was performed using stereo, optical, and scanning electron microscopy (HR-SEM and EDS) techniques. The microstructure of all fusion zones consists of two parts: a columnar zone, adjacent to the fusion boundary, and equiaxed grains, in the centre of the weld fusion zone. It is shown that the average width of the equiaxed zone present at the centre of the fusion zone increases with increasing welding speed. Metallographic examination shows that the highest welding speed (5 mm/s) results in the smallest average grain size. The welds prepared with high welding speed exhibit an increase in strength, hardness, and ductility compared with other welding speeds, which is attributed to low heat input.

Study on ultrasonic regulation of the welding performance and defects of 7A52 aluminum alloy plate

The welding performance and defects of thick aluminum alloy plates with medium and high strength are always a hot research topic. In this study, ultrasonic technology was used to regulate the properties and defects of welded joints of a 7A52 aluminum alloy plate during double-sided welding, and these welded joints were compared with conventional welded joints. X rays were used to macroscopically detect the defects of welded joints. An optical microscope was used to analyze the grain structure and microdefects in each zone of welded joints. The tensile and impact tests were carried out on the joints. The fracture morphology of tensile and impact specimens was observed using a scanning electron microscope, and the defects and slag inclusions were analyzed by energy dispersive spectroscopy. In the process of ultrasonic welding, the crystallization process of the molten metal pool was changed, and the solidification and heat transfer environment under ultrasonic influence directly led to the change in the properties and defects of welded joints. The experimental results show that the 7A52 aluminum alloy joints can produce deep penetration and very few macroscopic defects after ultrasonic adjustment. Ultrasonic waves can refine the grains in the weld zone, heat-affected zone, and fusion zone and reduce the microdefects in each zone. The tensile and impact properties of ultrasonic welds have been improved by 84% and 87%, respectively. Therefore, ultrasonic waves can regulate the welding performance and defects of 7A52 aluminum alloy plates and other aluminum alloy plates with a similar structural composition. This study provides guidance for the selection of a double-sided welding method with low cost, high efficiency, and good joint performance for aluminum alloy plates.

Study on microstructure and mechanical behavior relationship for laser-welded dissimilar joint of P92 martensitic and 304L austenitic steel

A dissimilar laser beam welded joint of ferritic/martensitic P92 steel, and 304L austenitic stainless steel (ASS) has been examined in as-weld and post-weld heat treatment (PWHT) at 760 °C for 120 min for microstructure feature and mechanical aspects. The microstructure of the weld metal, interface, and heat-affected zone (HAZ) was characterized in detail, and it was observed that a great level of inhomogeneity exists in a dissimilar joint. In addition, the effect of the inhomogeneity in microstructure on mechanical properties, microhardness, and impact strength of the welded joint was discussed. The welded joint's mechanical properties met the USC boiler requirement for both as-weld and PWHT situations. The welded joint showed a decent combination of tensile strength and impact strength for both as-weld and PWHT conditions. The tensile results showed the failure from the 304L SS base metal, which ensured the acceptable strength of the weld metal for the laser welded joints. The part of the welded joint with relatively poor impact strength was the weld metal. Though, the Charpy impact toughness of the weld metal (89 J) was measured higher than the ASME standard value (>41 J) and EN 1599:1997 standard value (>47 J) in the as-weld situation. The impact strength of the weld fusion zone was 138 J in PWHT condition.

Hybrid Products from Laser Powder Bed Fusion Manufactured Inconel 718 and 316L Utilizing Laser Welding

Additive manufactured (AM) 316L and Inconel 718 (IN718) parts using laser powder bedfusion technique and the weldability of the mixed pair by laser welding was investigated in this paper.The effect of prior heat treatment of the materials was also taken in to consideration. The motivationbehind this work was to investigate if hybrid products could be manufactured from these materials formore cost­efficient production of AM products. The results showed good reliability of the welds asthe tensile results were on par with the 316L base material. The hardness of the weld fusion zone was50 HV lower compared to the 316L base material hardness at 225 HV. In general, the results showedlaser welding is a very promising method for joining these printed materials and can be utilized asanother tool when integrating these materials into a design.

Stress Corrosion Cracking in Austenitic Stainless Steels in Reactor Primary Water–High Purity Oxidizing and in Supercritical Conditions

Abstract Austenitic stainless steels (SS) commonly used in the primary circuit of light water reactors (LWRs) have excellent corrosion resistance in demineralized (DM) water at high temperature (290°C–330°C) and pressure (7.4 MPa for boiling water reactor [BWR], 16 MPa for pressurized water reactor [PWR]). Radiolysis of primary DM water in BWR forms 200–300 ppb of oxidizing species (normal water chemistry [NWC]), which elevates the electrochemical potential of the SS from −300 to −600 mVSHE (mV with standard hydrogen electrode) when dissolved oxygen is 10–20 ppb to +100 to +200 mVSHE. Neutron irradiation of SS further induces metallurgical and microstructural changes, which compromises corrosion resistance. Thus, radiation makes BWR (NWC) environment hostile, causing extensive irradiation-assisted stress corrosion cracking (same as intergranular stress corrosion cracking [IGSCC]) in austenitic SS. IGSCC occurs in both sensitized (grain boundary chromium depletion) and nonsensitized conditions (strain-hardened region in base metal immediately adjacent to the weld fusion zone) and is a generic problem. IGSCC in BWR can be mitigated by hydrogen addition in water (hydrogen water chemistry [HWC]). BWR-HWC has limitations and is ineffective where boiling occurs. IGSCC of SS in PWR is limited because hydrogen addition in primary water suppresses radiolysis though the formation of aggressive environment in low-flow occluded regions can cause IGSCC in SS. Increasing demand for economic power has led to the primary environment in nuclear reactors to become hostile. Conceptual supercritical water reactor (SCWR) will use DM water at 500°C–600°C and 25 MPa, which is extreme for conventional LWR materials. IGSCC in austenitic SS and nickel-based alloys occurs in both oxidizing and reducing SCWR conditions, which can be further exacerbated by radiation. This article reviews how benign primary DM water becomes hostile in LWRs and extreme in SCWR conditions, causing SCC to be a generic problem in austenitic alloys.

Case Study About Resistance Projection Welding of Aluminized Steel Parts

Resistance projection welding is a non-polluting mechanized process used to obtain an assembly between similar or dissimilar metallic materials. The main advantages of this welding process are the possibility to achieve many different welded points at the same time and the long life of the electrodes compared to the spot-welding process. The paper analyses the effects of thin aluminium coating existing on mild steel parts of on the correct formation of welding points when assembling moulds for the manufacture of baking bread. From optical and electron microscopy analyses it resulted that some adjacent welded points show an interrupted fusion line, sprinkled with elongated islands of aluminium-rich compounds. The paper presents the effect of changing the values ​​of the welding parameters on the weld spot size, in correlation with the Al-rich inclusions that appear on the weld fusion zone. The best results have been obtained when the welding parameters values were the follows: electrode pressure of 2.6 bar, welding power of 19.18kVA and welding time of 7ms. The problems that occur when electric resistance welding of parts with aluminium coating have been highlighted, being useful for specialists who make products using this welding process.