Metal Weld Joints Research Articles

Tensile and impact toughness properties of various regions of dissimilar joints of nuclear grade steels

Abstract Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.

Structural, mechanical and corrosion studies of Cr-rich inclusions in 152 cladding of dissimilar metal weld joint

Cr-rich inclusions were discovered in 152 cladding at the inner wall of domestic dissimilar metal weld joint, and their morphologies, microstructures, mechanical properties and corrosion behaviors were systematically characterized by SEM, TEM, nanoindentation and FIB. The results indicate that the Cr-rich inclusions originate from large-size Cr particles in 152 welding electrode flux, and they are 50–150 μm in size in most cases, and there is a continuous transition zone of 2–5 μm in width between the Cr inclusion core and 152 cladding matrix, and the transition zone consists of Ni & Fe-rich dendritic austenite and Cr23C6 and Cr matrix. The transition zone has the highest nanoindentation hardness (7.66 GPa), which is much harder than the inclusion core (5.14 GPa) and 152 cladding (3.71 GPa). In-situ microscopic tensile tests show that cracks initialize preferentially in transition zone, and then propagate into the inclusion core, and creep further into 152 cladding after penetrating the core area. The inclusion core and its transition zone both share similar oxide film structure with nickel-base 152 cladding matrix in simulated primary water, while those two parts present better general corrosion resistance than 152 cladding matrix due to higher Cr concentration.

Local Ratcheting Response in Dissimilar Metal Weld Joint: Characterization Through Digital Image Correlation Technique

Ratcheting fatigue behavior of different alloys and their weld joints has been a topic of interest in the past few decades. However, little information is available about the ratcheting response in different zones, when a composite weld section is subjected to asymmetric loading cycle. This work aims at understanding the local ratcheting response in various zones of a dissimilar metal weld (DMW) joint. Digital image correlation technique has been used to measure local ratcheting strain components of a DMW joint. Accumulation of ratcheting strain in various zones of a DMW joint was found to be different, harder region accumulating negligible and softer region accumulating larger local ratcheting strain. Fatigue crack initiation or neck formation occurred in soft region owing to high ratcheting strain accumulation.

Development of electrodes for welding transmission pipelines and marine equipment made of high-strength low-alloy cold-resistant steels

The problems of production of welding electrodes with basic coatings in Russia is associated with the changes in the raw materials base used as components for electrode coatings, in particular, the electrodes of the UONII-13 series used extensively in industry in welding important structures made of cold-resistant low-alloy steels of different strength categories are examined. A promising composition of the electrode coating with a new deoxidation alloying system is proposed. The system results in high welding and technological characteristics of the electrodes and stable mechanical properties of the metal of welded joints in low-alloy steels with a strength of up to 560 MPa. The high-quality parameters are achieved as a result of using Minal (mineral alloy) in the electrode coating for adding through this coating the mineral and rare-earth components. The compositions of the coatings of the developed electrodes are calculated using the phase equilibrium diagrams of non-metallic systems.

Corrosion behavior of hydrogen charged super duplex stainless steel welded joints

The electrochemical behavior of the weld metal, heat‐affected zone (HAZ), and base material of super duplex stainless steel (SDSS) welded joints, made with the application of flux‐cored arc welding (FCAW) and submerged arc welding (SAW), were investigated with the use of metallographic examinations (optical microscopy and scanning electron microscopy), potentiodynamic polarization measurements and total hydrogen content determination in the initial state and after hydrogen charging. The obtained results revealed that the effect of hydrogen depended on the microstructure and type of the region of a welded joint. The highest amount of hydrogen penetrated the welded joint charged at 1 mA cm−2. It was observed in case of the FCAW‐welded joint, made with lower heat input. The electrochemical measurements showed that the base material was the most corrosion resistant part of the welded joint while the hydrogen charging strongly changed pitting and general corrosion susceptibility of HAZ and weld metal of both welded joints.

Структурні зміни в металі зварних з`єднань паропроводів після тривалої експлуатації

Структурні зміни в металі зварних з`єднань паропроводів після тривалої експлуатації

Structural changes in metal of welded joints of steam pipelines

Structural changes in metal of welded joints of steam pipelines

Influence of graded compositions and carbon diffusivities in buttering on structural integrity of dissimilar metal welds

Aim of the paper is to understand the effect of heterogeneity (graded composition) in buttering on the structural and mechanical properties in terms of integrity assessment of the dissimilar metal weld (DMW) joints. The metallurgical, microstructural and mechanical properties investigation of four types of DMW joints between SA508Gr.3Cl.1 (low alloy steel) and SS304LN (stainless steel) using an intermediate layer of Ni-Fe alloy in buttering as a graded composition have been carried out. The graded compositions and carbon diffusivities governs the microstructure in buttering deposits and that could directly affect the mechanical properties of the weld joints. These behaviours were investigated and explained in connection with the microstructural features those were changed due to mixed (graded) weld chemistry. The weld chemistry variations due Ni-Fe layer have significantly affects the distortion behaviour of the joints. The graded composition and associated carbon diffusivities due to Ni-Fe layers have confirmed the positive changes in the yield strength mismatch behaviour, plastic instability strength, tensile properties, interfacial properties and metallurgical properties. The measure of yield strength ratio has been modified in accordance to the distinctive regions in the dissimilar metal joints. Such modifications are suggested in structural integrity procedure for DMW joints. Moreover, the need of graded compositions has been justified for the improved metallurgical, structural and mechanical properties in nuclear power plant system. These variations and modifications are important for realistic structural integrity of DMWs in nuclear power plants.

Development of Slag Base for Welding Fluxes from Man-Made Mineral Formations of Ural Mining and Smelting Companies

Slag bases for welding materials have been developed from mineral raw materials and man–made mineral formations of the Urals. Successful comprehensive studies and tests of fused fluxes and also of weld metal and weld joints obtained by these welding materials have been carried out. It has been clearly established that the obtained weld metal has low content of harmful impurities ([S] is as low as 0.01 wt%) due to the use of the electric arc furnace method, purity of the feedstock minerals and technogenic raw materials and physicochemical reactions during the welding process.

Microstructure-dependent fracture toughness (JIC) variations in dissimilar pipe welds for pressure vessel system of nuclear plants

In present study, dissimilar metal weld (DMW) joints between SA508Gr.3cl.1 ferritic steel and SS304LN pipes were prepared using Inconel 82/182, and Inconel 52/152 consumables. Metallurgical properties and their influence on fracture toughness of weldment regions and interfacial regions could play a significant role in integrity assessment of these joints. Ni-based consumables exhibit complex metallurgical properties at interfacial regions. The metallurgical characterization and fracture toughness studies of Inconel 82/182 and Inconel 52/152 joints have been carried out for determining the optimum consumable for DMW joint requirements and the effect of microstructure on fracture toughness in weldment regions. The present codes and procedures for integrity assessment of DMW joints have not given due considerations of metallurgical properties. The requirements for metallurgical properties by considering their effect on fracture toughness properties in integrity assessment have been discussed for reliable analysis. Inconel 82/182 is preferred over Inconel 52/152 joints owing to favorable metallurgical and fracture toughness properties across the interfacial and weldment regions.

Fractal Geometry in Metallurgy of Welding and Coatings

Application of new methods for the description of structure of metals and alloys, the identification of new quantitative structure-morphology tours are especially important to establish the relationship "structure - property" and predicting the properties of weld metal on the basis of mathematical modeling. In our work we applied a fractal approach to the analysis of following objects: structure of metal during welding, fatigue fracture surface of metal of welded joints, structure of coatings in microarc oxidation, macrostructure of the heat-resistant steels during electron beam welding

Creep behavior of dissimilar metal weld joints between P91 and AISI 304

Dissimilar welds between ferritic creep-resistant steels and austenitic stainless steels in power plant service are known to fail prematurely due to a large difference in their thermal coefficient of expansion. To address this problem, in the current work, modified 9Cr-1Mo steel (P91) and austenitic stainless steel (AISI 304) transition joints were produced using friction welding employing three interlayers: Inconel 625, Inconel 600, and Inconel 800H. These interlayers were friction welded one over another on P91 alloy, which was finally friction welded to AISI 304. The joints produced with single and three interlayers were subjected to creep rupture tests at different temperatures and stress levels. The creep test results demonstrated that the proposed approach can help realize striking improvements in creep performance of P91/AISI 304 dissimilar metal welds. Further, analysis of creep resulted in a stress exponent (n) of 3 by incorporating the concept of threshold stress which suggested the creep deformation mechanism to be viscous glide due to solute drag. Creep rupture data was also analyzed using Monkman-Grant relationship and creep damage tolerance factor (λ). Results indicated that the damage mechanism is due to cavity growth by the combined effect of power law and diffusion creep.

Stress corrosion cracking of fusion boundary for 316L/52M dissimilar metal weld joints in borated and lithiated high temperature water

The stress corrosion cracking (SCC) crack growth rates (CGRs) at the fusion boundary (FB) for 316L/52M weld joints were measured using direct current potential drop systems in borated and lithiated high temperature water. The cracks propagated along the FB and were blocked after propagating into the composition transient zone. The cracking mode is both intergranular and transgranular. The CGRs at the FB are similar to those in the heat-affected zone (HAZ) in oxygenated water, but slightly higher than those in the HAZ in hydrogenated water. The temperature dependences of CGR in both hydrogenated and oxygenated water are discussed.

Microstructure and Mechanical Properties of Dissimilar Metal Weld Joint between VM12-SHC and X20 Martensitic Steels

In this paper, X20 and VM12-SHC martensitic steels were welded by tungsten inert gas (TIG) process. The microstructural and mechanical properties of the dissimilar weld joint were investigated. Results obtained indicated that the weld was comprised of typical tempered martensite microstructure. VM12 base metal (BM) had fine lath martensite while X20 consisted of large clusters of tempered martensite. Delta ferrite was distributed throughout the entire weld. The EDX results confirmed the presence of M23C6 and MC precipitates found on the grain boundaries and the matrix. Hardness test results revealed that the X20 CG-HAZ had exceeded the maximum hardness of 350HV-10, as per PN-EN 15614-1 and PN-EN 12952-6 standards for heat treated joints.

Tensile properties of shielded metal arc welded dissimilar joints of nuclear grade ferritic steel and austenitic stainless steel

AbstractIn nuclear power plants, modified 9Cr-1Mo ferritic steel (Grade 91 or P91) is used for constructing steam generators (SG’s) whereas austenitic stainless steel (AISI 316LN) is a major structural member for intermediate heat exchanger (IHX). Therefore, a dissimilar joint between these materials is unavoidable. In this investigation, dissimilar joints were fabricated by Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. Transverse tensile properties and Charpy V-notch impact toughness for different regions of dissimilar joints of modified 9Cr-1Mo ferritic steel and AISI 316LN austenitic stainless steel were evaluated as per the standards. Microhardness distribution across the dissimilar joint was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. The transverse tensile properties of the joint is found to be inferior to base metals. Impact toughness values of different regions of dissimilar metal weld joint (DMWJ) is slightly higher than the prescribed value. Formation of a soft zone at the outer edge of the HAZ will reduce the tensile properties of DMWJ. The complex microstructure developed at the interfaces of DMWJ will reduce the impact toughness values.

Using friction welding for producing heat exchanger equipment from martensitic 15Kh5M steel

The results of mechanical and other types of tests of metal of welded joints in pipe blanks of 15Kh5M martensitic steel, produced by friction welding with rotation, are presented. On the basis of the analysis of the test results it is concluded that 15Kh5M can be efficiently welded by friction welding and that the method can also be used for producing the tube–tube plate sections of heat exchangers made of 15Kh5M steel with appropriate modernization of welding equipment.

Microstructure of a safe-end dissimilar metal weld joint (SA508-52-316L) prepared by narrow-gap GTAW

The microstructure, residual strain and interfacial chemical composition distribution of a safe-end dissimilar metal weld joint (DMWJ, SA508-52-316L) prepared by narrow-gap gas-tungsten arc welding (NG-GTAW) were studied by optical microscope (OM) and scanning electron microscope equipped with an energy dispersive X-ray microanalysis (SEM/EDX) and an electron back scattering diffraction (EBSD) system. Complex microstructure and chemical composition distribution are found, especially at the SA508-52 interface and the 52-316L interface. In brief, a complicated microstructure transition exists within the SA508 heat affected zone (HAZ); the residual strain, the fraction of high angle random grain boundaries and low angle boundaries decrease with increasing the distance from the fusion boundary in 316L HAZ; neither typical type II boundary nor obvious carbon-depleted zone is found near the SA508-52 interface; dramatic and complicated changes of the contents of the main elements, Fe, Cr and Ni, are observed at the distinct interfaces, especially at the SA508-52 interface. No carbon concentration is found at the SA508-52 interface.

Mechanical Properties and Phase Transformations in Resistance Spot Welded Dissimilar Joints of AISI409M/AISI301 Steel

Objectives: In this study, the mechanical properties and phase transformations of resistance spot welded dissimilar joints between austenitic stainless steel AISI 301 and ferity stainless steel AISI 409M are investigated. Methods/Analysis: Mechanical properties such as tensile shear strength, failure energy, failure mode, nugget size and surface indentation were analysed at varying current ratings. Macrostructure was examined for size and shape. Microstructure at various locations such as, fusion zone and heat affected zones were investigated. Micro hardness measurement was done at various locations along the weld. Findings: Tensile shear strength increases with increase in welding current in expulsion free welds. Fusion zone hardness was found to be larger than that of both base metals and heat affected zones. Nugget size and energy absorbing capacity of the spot weld were found to be in correlation with weld current in expulsion free samples. Electrode indentation on the nugget surface increases with increase in welding current. Fusion zone microstructure consists of martensite and ferrite. Asymmetrical nugget shape was observed. Novelty/Improvement: Investigating the effects of resistance spot welding on the mechanical properties and phase transformations of ferritic-austenitic dissimilar metal weld joint.

Comparison of procedures for evaluation of effect of welding thermal cycle on impact toughness of HAZ metal of welded joints from low-alloy steels

Comparison of procedures for evaluation of effect of welding thermal cycle on impact toughness of HAZ metal of welded joints from low-alloy steels

Metallurgical Behaviour and Carbon Diffusion in Buttering Deposits Prepared With and Without Buffer Layers

Use of a buttering deposit on ferritic steel in dissimilar metal weld (DMW) joint is a common practice in nuclear plants to connect pressure vessel components (ferritic steel) to pipelines (austenitic stainless steel). Carbon migration and metallurgical changes near fusion interface (ferritic steel–austenitic stainless steel) lead to a steeper gradient in material properties, and minimizing this gradient is the major challenge in the manufacturing of DMW joints. Inconel 82 is often deposited on ferritic steel material as buttering to reducing the gradient of physical and attaining material compatibility. Inconel 82/182 fillers are used to minimize the carbon migration, but the results are not truly adequate. In this paper, Ni–Fe alloy (chromium-free) has been used as the intermediate buffer layer in the weld buttering deposit to address the issue of carbon migration and subsequent metallurgical deterioration. The weld pads with and without buffer layers of Ni–Fe alloy have been investigated and compared in detail for metallurgical properties and carbon diffusivities. Ni–Fe buffer layer can significantly control the carbon migration which resists the metallurgical deterioration. It showed the better results in post-weld heat treatment and thermally aged conditions. The buttering deposit with Ni–Fe buffer layer could be the better choice for DMW joints requirements.