Austenitic Steel Weld Research Articles

Welding of High-Nitrogen Austenitic Steels (Review)

Welding of High-Nitrogen Austenitic Steels (Review)

Effect of post weld heat treatment on the structure and mechanical properties of explosive welding of austenitic steel 321 - aluminum 1050 - aluminum 5083

Effect of post weld heat treatment on the structure and mechanical properties of explosive welding of austenitic steel 321 - aluminum 1050 - aluminum 5083

Dissimilar welding of austenitic and ferritic steels using nickel and stainless-steel filler: Associated issues

The microstructure development and mechanical behaviour of dissimilar metal welds between ferritic and austenitic steel, as well as their application in nuclear power plants, are discussed in this review paper. Nuclear reactor components, such as steam generators and pressure vessels, consist primarily of SA508 due to their low cost and high operating temperatures and pressures. The welding of dissimilar metals is crucial due to variations in physical characteristics such as thermal conductivity, thermal expansion coefficient, mechanical properties and chemical compositions. The principal challenges of dissimilar ferritic and austenitic steel welding are the subject of this review work. Weldability issues include a sharp change in mechanical and metallurgical characterization across the fusion line, carbon migration, cyclic thermal stresses and residual stresses, which necessitate a thorough investigation of the welded joint. Generally, austenitic steel and nickel-based fillers are used to join austenitic and ferritic steel materials; however, owing to many weldability concerns, nickel-based consumables are replacing austenitic consumables. Another critical issue in the weld joint is the selection of appropriate welding consumables, and detailed explanations of the benefits of employing a buttering layer on the ferritic side are provided. The effect of heat treatment on the metallurgical and mechanical characteristics of the weld joint, as well as the formation of residual stress, has also been thoroughly explored.

Achieving superior cryogenic impact toughness and sufficient tensile properties in a novel high-Mn austenitic steel weld metal via cerium addition

The microstructure and mechanical properties of the novel cryogenic high-Mn austenitic steel weld metals with different cerium (Ce) contents were investigated via electron back-scattered diffraction, scanning and spherical aberration-corrected transmission electron microscopy, and cryogenic impact and tensile test. The results indicated that the crystallographic grain size was significantly refined, and the relative frequency of high-angle grain boundaries increased with the increase of Ce content. Ce element addition could modify the main inclusions from irregular Al2O3 into regular Ce-containing inclusions. Meanwhile, the inclusions gradually became fine and dispersed, and the volume fraction of inclusions decreased with the increase of Ce content from 0 to 870 ppm. The increase of Ce content continuously improved cryogenic impact toughness from 82 J to 116 J, and yield strength, tensile strength and total elongation all increased to different degrees. We found that in addition to the beneficial changes in inclusion modification, grain refinement and increase in the proportion of high-angle grain boundaries, the solid solution of Ce also played a crucial role in the mechanical properties.

Hot Corrosion Behavior of Fe–Cr–Ni-Based Austenitic Heat-Resistant Steel Weld Metal in Na2SO4–NaCl Molten Salts at Different Temperatures

The hot corrosion behavior of the austenitic heat-resistant steel weld metal produced by multi-pass gas tungsten arc welding was investigated. A bilayer oxide scale formed on the surface of the weld metal by the selective oxidation of the element Cr and Fe, and the dissolution of the oxide film occurred at elevated temperatures due to the existence of the molten salt. Morphologies and structures of the oxide scale were characterized by electron microscopy and X-ray diffraction techniques, and then the underlying reason for the hot corrosion of the nonequilibrium weld metal was identified. The interdendritic region could act as the shortcut path for the oxygen, which promotes the internal oxide distribution in chains, and a large internal oxidation zone appears under the bilayer oxide scale.

Dissimilar welding of 316L austenitic steel with DOCOL 1200 M steel for the structures in automotive industry

Dissimilar welding of 316L austenitic steel with DOCOL 1200 M steel for the structures in automotive industry

Effect of cerium on microstructure and microsegregation behavior of novel cryogenic high-Mn austenitic steel weld metal

The novel cryogenic high-Mn austenitic steel weld metal with four different cerium (Ce) contents were prepared under submerged arc welding by adding cerium dioxide and calcium silicon reducing agents into the flux to refine the solidification structure and alleviate the microsegregation. The effects of the Ce element on the microstructure, inclusion, and microsegregation behavior of weld metal were systematically investigated via optical, scanning, and transmission electron microscopy and using an electronic probe micro-analyzer. The results showed that the dendrite arm spacing of high-Mn austenitic steel weld metal was significantly reduced with an increase in the Ce content from 0.018 to 0.087 wt%. The typical inclusions in the weld metal were mainly Al2O3, CeAlO3, Ce2O3, and Ce2O2S for the Ce content ranging from 0 to 0.087 wt%. The number density and the size distribution of effective inclusions influenced the microstructure variation. Numerous small-sized effective inclusions (Ce2O3 and Ce2O2S) in the weld metal with 0.087 wt% Ce were distributed at the dendrite core, promoting the nucleation for austenite during the solidification and refining the dendrite structures. The co-segregation of Mn, C and Si occurred in the interdendritic regions. The segregation ratio of Mn, C and Si gradually decreased with the increase in Ce content, alleviating the element microsegregation.

Evolution of inclusions in novel cryogenic high-Mn austenitic steel weld metal with cerium addition

Cerium (Ce) was effectively transitioned into the high-Mn austenitic steel weld metal under submerged arc welding by adding cerium dioxide and calcium silicon reducing agents into flux. The evolution behaviours of the composition, number density and size of inclusions in weld metal with different Ce contents were systematically investigated by thermodynamic calculation and experiments. The results show that the number density of inclusions increased and average size decreased with the increase of Ce content from 0 to 0.087 wt-%. Meanwhile, and the percentage of inclusions number with size less than 0.80 μm increased from 79.28% to 91.43%. The evolutionary process of inclusions was Al2O3 → Al11O18Ce → CeAlO3 → Ce2O3 → Ce2O2S with the increase of Ce content in the present weld metal. In particular, Ce-O-S-Al inclusion was extracted by in-situ sample preparation method, which proved its internal structure and evolution process. The complete formation model of Ce-Al-O-S system was also established.

Study on narrow gap welding of martensitic grade P92 and austenitic grade AISI 304L SS steel for ultra-supercritical power plant application

Study on narrow gap welding of martensitic grade P92 and austenitic grade AISI 304L SS steel for ultra-supercritical power plant application

Elucidating microstructural evolution and its effect on the mechanical properties of FSWed alumina-forming austenitic steel for power plant applications

Alumina-forming austenitic (AFA) steel is considered as a promising candidate used for advanced energy systems. Fusion welding of austenitic steels usually requires the introduction of a certain delta (δ) ferrite to avoid thermal cracking, but for the AFA steel, the presence of δ ferrite will greatly accelerate the precipitation of hard and brittle sigma (σ) phase at its target service temperature.In this work, for the AFA steel with a typical composition, we demonstrated a superior capability of friction stir welding (FSW) in avoiding the formation of δ and σ phases, and developing the favorable weld microstructures under various welding conditions. The microstructure evolution of AFA steel during FSW with various rotational speeds (300–700 rpm) was studied in detail. The resulting FSW joints all exhibit higher yield strength (YS) and ultimate tensile strength (UTS) than the base metal, especially at low rotational speed, while retaining reasonable ductility, despite decreasing with reducing rotational speed. The associated relationship between the microstructure and mechanical properties of the resulting FSW joints was well correlated. This work provides an effective method to obtain the fully-austenitic welded joints of AFA steel with excellent strength-ductility synergy.

Deep Learning Based Inversion of Locally Anisotropic Weld Properties from Ultrasonic Array Data

The ability to reliably detect and characterise defects embedded in austenitic steel welds depends on prior knowledge of microstructural descriptors, such as the orientations of the weld’s locally anisotropic grain structure. These orientations are usually unknown but it has been shown recently that they can be estimated from ultrasonic scattered wave data. However, conventional algorithms used for solving this inverse problem incur a significant computational cost. In this paper, we propose a framework which uses deep neural networks (DNNs) to reconstruct crystallographic orientations in a welded material from ultrasonic travel time data, in real-time. Acquiring the large amount of training data required for DNNs experimentally is practically infeasible for this problem, therefore a model based training approach is investigated instead, where a simple and efficient analytical method for modelling ultrasonic wave travel times through given weld geometries is implemented. The proposed method is validated by testing the trained networks on data arising from sophisticated finite element simulations of wave propagation through weld microstructures. The trained deep neural network predicts grain orientations to within 3° and in near real-time (0.04 s), presenting a significant step towards realising real-time, accurate characterisation of weld microstructures from ultrasonic non-destructive measurements. The subsequent improvement in defect imaging is then demonstrated via use of the DNN predicted crystallographic orientations to correct the delay laws on which the total focusing method imaging algorithm is based. An improvement of up to 5.3 dB in the signal-to-noise ratio is achieved.

Comparative Research of Microstructure and Mechanical Properties of Stainless and Structural Steel Dissimilar Welds.

The present study utilized a metal inert gas welding (MIG) to make a dissimilar weld of stainless steel AISI 304, 314, 316L, 420 grades and a standard structural steel S355MC. It refers to a weld joining two materials from different alloy systems commonly used in heat exchangers, pressure vessels, and power plant systems. Obviously, maintaining the integrity of such welds is of paramount importance to the safety issues. Therefore, detailed microscopic and experimental studies were performed to evaluate the reliability of these welds. The microscopic analysis did not reveal any presence of weld defects such as porosity or cracks, which ensured that MIG process parameters were properly selected. The performance of dissimilar welds was assessed by hardness and tensile tests. The hardness profiles revealed differences between austenitic and martensitic steel welds that later showed extremely high values in the heat-affected zone (HAZ), which caused fractures in this zone during tensile test. The welds of all austenitic steel grades withstood the tensile test, showing an average tensile strength of 472 MPa with fractures observed in the base metal zone. It made clear that the use of a filler rod 308LSI is suitable only for the austenitic stainless and structural steel dissimilar welds and not appropriate for martensitic-structural steel welds. The achieved results revealed that the higher hardness of the martensitic phase in the HAZ of AISI 420 is closely related with the formation of untempered coarse martensitic structure and higher carbon content.

Laser welding of new austenitic cryogenic corrosion-resistant steels alloyed with nitrogen

The article proposes a method for improving the thermal performance of walking beam reheating furnaces using a statistical mathematical model of metal heating. The main part of the study refers to the creation of a metal heating model based on a comprehensive analysis of 15 industrial experiments carried out on the Russian continuous furnaces. The first stage of statistical model creation consists of factors’ selection, construction of regression model, correlation analysis and assessment of the variables’ significance, adjustment of factors and obtaining regression equations. As a result, a quasi-dynamic statistical mathematical model of a five-zone walking beam reheating furnace has been created and adapted, that actually makes it possible to trace the heating process in dynamics. The adaptation of the statistical model and error calculation has been carried out using the results of industrial experiments on the investigated furnaces of mills 2000 and 5000. The article contains graphs comparing real temperatures and temperatures calculated on the basis of mathematical and statistical models for one of the experiments. The second stage of quasidynamic statistical model creation has shown that temperature of the combustion products of neighboring zones is a significant factor, that enhances calculation accuracy by 1-3%. The main conclusions are formulated based on the results of the research done. For the first time in metallurgical practice, a quasi-dynamic statistical model has been developed and adapted which describes the process of metal heating in a walking beam reheating furnaces. Since the regression function is defined, interpreted and justified, and the assessment of the accuracy of the regression analysis meets the requirements, it can be assumed that the model and predicted values have sufficient reliability.

Laser welding of new austenitic cryogenic corrosion-resistant steels alloyed with nitrogen

There were studied structures and properties of welded joints of laboratory melted austenitic steels: Fe-0.04C-18Cr-9Ni-0.2N and new-developed Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu. Correct choice of composition and deformation-heat treatment leads the new-developed steels are high-strength corrosion-resistant ones with stable austenite. Computer simulation shows that enough quality of welded seam can be provided by laser welding of plates of up to 4 mm in thick at the room temperature. For bigger thicknesses preliminary heating is necessary. Microstructure, phase compositions, lattice periods, X-ray diffraction peak broadening, microhardness, bending strength and ductility, resistance against intercrystalline, pitting and total corrosion was studied for bulk metal and laser welded joints of high-temperature thermomechanically treated hot-rolled plates, including tests after 1000 thermal cycles in range –163…+20 °C were investigated. It was shown that welded seams are 300…1000 μm in wide and have no porosity and no thermal affected zone. The welded seam strength is the same as for bulk metal, 180° bend test shows no cracks in the seam. The resistances of welded seam and bulk of Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu steels against total corrosion in the sea water (3 % NaCl) and in acid environment (0,5M H2SO4, including additional blowdown by H2S), pitting and intercrystalline corrosion in standard environments are practically equal. The structures, phase compositions, hardnesses and corrosion resistances of welded joints of both new-developed steels are constant after the thermocycling.

Weld Metal Microstructure Prediction in Laser Beam Welding of Austenitic Stainless Steel

In the present work an approach to weld metal microstructure prediction is proposed, based on an analytical method that allows the evaluation of the thermal fields generated during the laser beam travel on thick plates. Reference is made to AISI 304L austenitic steel as a base material, with the aim to predict the molten zone microstructure and verify the best condition to avoid hot cracking formation, which is a typical issue in austenitic steel welding. The “keyhole” full penetration welding mode, characteristic of high-power laser beam, was simulated considering the phenomenological laws of conduction by the superimposition of a line thermal source along the whole thickness and two point sources located, respectively, on the surface and at the position of the beam focus inside the joint. This model was fitted on the basis of the fusion zone profile, which was experimentally detected on a weld seam obtained by means of a CO2 laser beam, in a single pass on two squared edged AISI 304L plates, that were butt-positioned. Then the model was applied to evaluate the thermal fields and cooling rates, the fusion zone composition and the solidification mode.

Analysis of Flaw Detection Sensitivity of Phased Array Ultrasonics in Austenitic Steel Welds According to Inspection Conditions.

The anisotropy and inhomogeneity exhibited by austenitic steel in welds poses a challenge to nondestructive testing employing ultrasonic waves, which is predominantly utilized for the inspection of welds in power plants. In this study, we assess the reliability of phased array ultrasonic testing (PAUT) by analyzing the flaw detection sensitivity of ultrasonic beams in anisotropic welds, based on the inspection conditions. First, we simulated the sectorial scan technique, frequently employed for the inspection of actual welds, while taking into account the ultrasonic wave mode, frequency, and shape and position of a flaw. Subsequently, we analyzed the flaw sensitivity by comparing A-scan signals and S-scan results. The sensitivity analysis results confirmed the detection of all flaws by considering at least two inspection methods based on the shape and position of the flaw. Furthermore, we verified our model by performing an experiment under the same conditions as the simulation and found that the results were in agreement. Hence, we find that the simulation modeling technique proposed in this study can be utilized to develop suitable inspection conditions, according to the flaw characteristics or inspection environment.

시뮬레이션을 통한 오스테나이트 강 용접부에서 위상배열초음파의 전파특성 연구

시뮬레이션을 통한 오스테나이트 강 용접부에서 위상배열초음파의 전파특성 연구

Numerical and Metallurgical Analysis of Laser Welded, Sealed Lap Joints of S355J2 and 316L Steels under Different Configurations.

This paper presents the results of laser welding of dissimilar joints, where low-carbon and stainless steels were welded inthe lap joint configuration. Performed welding of austenitic and ferritic-pearlitic steels included a sealed joint, where only partial penetration of lower material was obtained.The authors presented acomparative study of the joints under different configurations. The welding parameters for the assumed penetration were estimated via anumericalsimulation. Moreover, a stress–strain analysis was performed based on theestablished model. Numerical analysis showed significant differences in joint properties, therefore, further study was conducted. Investigation of the fusion mechanism in the obtained joints wascarried out using electron dispersive spectroscopy (EDS) and metallurgical analysis. The study of the lap joint under different configurations showed considerable dissimilarities in stress–strain distribution and relevant differences in the fusion zone structure. The results showed advantages of using stainless steel as the upper material of a microstructure, and uniform chemical element distribution and stress analysis is considered.

Characterization of hot cracking in multi-pass weld metal of high manganese austenitic steel

ABSTRACT In multi-pass welding of high manganese austenitic steel, weld metal is solidified in austenite single phase and hot cracking may occur depending on residual stress. In order to identify the cracking morphology, a fracture surface of the cracking of weld metal in multi-pass welding test was observed. The fracture surface indicated a dendritic morphology and a bunching pattern; therefore, it is considered that the crack in the multi-pass weld metal is caused by residual liquid film or remelting liquid film. Varestraint test was carried out in order to clarify the characterization of the crack, and then the fracture surface of cracks obtained by the test was observed. Transverse-type and longitudinal Varestraint test were used for getting typical fracture surfaces of solidification cracking in weld metal, and liquation cracking in reheat weld metal and heat affected zone of base metal, respectively. Comparing the fracture surfaces of cracks of Varestraint test and crack in practice, the fracture surface of the solidification cracking was most similar to the crack in multi-pass weld metal in this study. Thus, it is considered from comparing the fracture surfaces that solidification cracking might mainly occur in the multi-pass welding of the high manganese steel.

Metallurgical Effect of Rare-Earth Lanthanum Fluoride and Boride in the Composite Coating of Wires in the Arc Welding of Bainitic-Martensitic and Austenitic Steel

For arc welding of high-strength and cold-resistant steels, the author developed an advanced design of steel wire with a micro-composite coating of a nickel matrix and nanoparticles of LaF3 and LaB6, which improves the metallurgical influence of rare-earth elements (REE) and forms refractory sulphides and oxides of REE, as well as boron nitride. The addition of 0.1–0.3 wt% La in the weld pool leads to an increase in the content of the refractory compounds La2O3, LaO2, and LaS, and to the reduction in the content of the low-melting and brittle oxides and sulphides SiO2, SiO, MnO, MnS, and SiS. The use of steel wire with the composite coating of LaF3 and LaB6 allows for microstructural refinement when welding S960QL bainitic-martensitic steel and X70 API bainitic steel, and increases the impact toughness of the welds by 1.17–1.6 times.