Weld Seam Metal Research Articles

Determination of the temperature dependence of the fracture toughness of the metal of a thick-walled shell taking into account the inhomogeneity of the material

The estimates of the reference temperature T 0 , obtained for the base metal and the weld-seam metal of the Cr - Ni - Mo - V type (shell 200 mm thick) on the basis of statistical modeling by the Monte Carlo method are presented. T 0 was determined according to the ASTM E1921 standard taking into account the inhomogeneity of the material. The sample size of the fracture toughness values KJC for T 0 modeling was 12, 24 and 70. The Monte Carlo method was used for analysis of the correctness of metal identification (homogeneous/inhomogeneous). It is shown that sampling of 12 samples do not provide a reliable determination whether the metal is homogeneous or inhomogeneous (incorrect results were obtained in 50% of cases for the base metal and in 37% of cases for the weld-seam metal). When the sample size increased to 24 samples, the incorrect results were obtained in 5% of cases. The T 0 values with allowance for the material inhomogeneity were determined by two ways: using a screening procedure and proceeding from the actual bimodal representation of the fracture toughness distribution (parameters of the bimodal distribution were determined by the maximum likelihood method). It is shown that both methods give close results for the base and weld-seam metal, the magnitude of the shift towards positive values in the average T 0 values determined with allowance for the inhomogeneity being about 22°C. Using the obtained T 0 estimates, the lower envelopes of the temperature curves of the fracture toughness are constructed (master curves for 5 % failure probability).

Influence of filler metal on microstructure and properties of titanium/copper weld joint by GTAW weldments

Gas tungsten arc welding (GTAW) is a widely used joining technique due to its low welding cost and flexible process. To promote the application of titanium/copper dissimilar metal welded structure, the microstructures and properties of TA2 titanium and T2 copper butt joint prepared by GTAW with pure copper filler metal (S201) and Cu–Al filler metal (S214) were systematically investigated. The microstructures of the joints were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), and the properties of the joints were evaluated by tensile, microhardness and electrochemical corrosion tests. The results suggested that the intermetallic compound layers of S201 filler metal weld joint were composed of rod-like Ti2Cu, plate-like TiCu, needle-like TiCu and a small amount Ti3Cu4. While plate-like TiCu were not found when using S214 filler metal. Moreover, the weld joint with S201 filler metal displayed a better plasticity and a higher tensile strength having 73.0% tensile strength of copper base metal. The electrochemical corrosion tests indicated that Al elements in weld joint with S214 filler metal could inhibit the cathodic reaction, and decrease the dissolution of weld seam metal.

Влияние высоких температур на механические свойства металла шва сварного соединения малоуглеродистой низколегированной стали

The mechanical properties of the seam metal of a low-carbon low-alloy steel welded joint of the 22K type (Russian standard) have been investigated when testing for uniaxial tension in the temperature range from room temperature to 1200 °C. A comparative analysis of the changes in the structure, the strength and plastic properties of base metal and weld seam metal in the selected temperature range was carried out.

Heat transfer and metal flow behavior of AA7075 high-strength aluminum alloy in a new current-induced friction stir welding with a multi-physics field model based on the inverse method and parameter scanning batch processing technique

A new multi-physics field mathematical model is established to describe an advanced current-induced friction stir welding (CFSW) process. A reverse method and large-batch parameter scanning technique are used to analyze the influence of the axial force, welding rotational speed ratio, and current on the temperature field, flow field, residual strain, and stress field of CFSW. The thermal-force comprehensive effect of the additional current is studied in CFSW. The research results show that the hybrid current can achieve effective metallurgical bonding as a new current-induced friction stir welding mode, when the effective welding joint cannot be obtained due to insufficient heat input in traditional FSW. The high-temperature zone area of CFSW is larger than that of conventional FSW, and the hybrid current is helpful to reduce residual stress and strain. The additional current can increase the flow velocity of metal in welding seam, but it has little influence on the flow path and pattern of welding seam metal. More importantly, CFSW process allows higher welding speed and lower axial force owing to auxiliary resistance heat compared with traditional FSW, which makes CFSW able to achieve higher production efficiency and save tool cost. The three-dimensional multi-physics field mathematical model of CFSW is reliable and correct in this paper.

Mechanism of Change In VVER-440, -1000 Vessel Material Properties in Irradiation–Recovery Annealing–Irradiation Cycle

The efficacy of recovery annealing of weld-seam metal for VVER vessel service life extension is examined. A comparative complex assessment of the degradation of VVER-440, -1000 weld-seam metal, as most subjected to radiation embrittlement due to operational factors, is presented. The main difference of the recovery annealing regimes associated with differences of their chemical composition and structural-phase state as well as the mechanisms of the degradation of the structure and properties during operation is substantiated. Comparative studies of the recovery of the structural state and mechanical properties of weld-seam metal after annealing in the chosen regimes as well as radiation embrittlement during re-irradiation were performed.

Evaluation of Influence of Thermal Methods of Metal Separation Cutting on Welding Quality

We have investigated a possibility of obtaining high-quality welded joints after oxygen and plasma cutting of steel С355 without removing the heat-affected zone (HAZ), in which the changes in chemical, phase and structural compositions are observed. Numerical and experimental studies of the effect of heat input of MAG and Submerged Arc welding on the quality of welded joints are performed. In particular, it was found that when the heat input of welding is at least 6.5 kJ/cm, the metal of HAZ of the edges after cutting is heated during the welding to temperatures above Ас3, which leads to its full recrystallization. When the heat input of welding is at least 10 kJ/cm, the edges after cutting are completely melted and become a part of the welding seam metal. The presence of extensive areas of melting and recrystallization of the edges in the welding process contributes to obtaining high-quality welded joints without removing the HAZ of the edges after cutting. To verify the results of numerical studies, experimental tests of control welded joints were conducted, which showed that the values of bending angle and impact toughness of the welding seam metal and heat affected zone are significantly above the regulatory requirements to quality of welded joints, and not less than the same requirements for steel С355. The obtained results confirm the possibility of revising domestic regulatory requirements for the steel constructions production in terms of the preparation of edges for welding using technologies of thermal cutting without subsequent machining.

METALLOGRAPHIC INVESTIGATIONS OF QUALITY OF WELDING SEAM OBTAINED BY SILICOMANGANESE SLAG FLUX WELDING

Results of the study of metallurgical wastes application as components of welding fluxes are given. Composition and production technology of a new welding flux using silicomanganese slag as a component have been developed. Results of this slag application in manufacture of welding fluxes are presented. In order to study quality of welded seams, metallographic analysis was carried out and the grain size and level of nonmetallic inclusions contamination were determined. Metallographic studies were made with the help of OLYMPUS GX-51 optical microscope in magnification range of 100 – 1000 times. Influence of fractional composition of fluxes on their welding technological properties was studied. Optimal fraction was selected, ensuring low level of contamination of metal of welding seam with non-metallic oxide inclusions, in particular non-deformable silicates and oxides. It has been established that application of welding flux fine fraction in an amount of 30 – 40 % ensures reduction in degree of welding seam metal contamination with non-metallic inclusions. The metallographic analysis of welding seam metal shows that introduction of fine fraction does not affect its structural components. Welding seam metal has a ferrite-pearlite structure; ferrite is presented in form of non-uniform grains elongated in the direction of heat extraction. It was determined that the optimum content of a fraction less than 0.45 mm in the flux is 30 – 40 %. To raise technical and economic indicators, it is suggested to mix fine fraction with liquid glass. Application of ceramic flux made of silicomanganese slag dust of 0.45 mm fraction, bonded by liquid glass, provides reduction in the welding seam metal level of contamination with nonmetallic inclusions. At the same time, increase in its volume from 15 to 40 % does not significantly affect the level of welding seam metal contamination with nonmetallic inclusions and its microstructure. Microstructure of welding seam metal is represented by perlite and ferrite. It was found that fine fraction introduction with use of liquid glass in an amount of 15 – 20 % is optimal in production of ceramic flux.

Effect of the process parameters on the three-dimensional shape of molten pool during full-penetration laser welding process

The present study designs a low-cost method for determining the three-dimensional (3D) shape of a molten pool formed during a laser full penetration welding process and verifies the feasibility and reproducibility of this method. A dissimilar metal is introduced into the molten pool at the instant when the laser full penetration welding process is about to finish. Under intense stirring, the dissimilar elements are rapidly distributed in the entire molten pool. After the molten pool rapidly solidifies, the 3D shape of the region of the weld seam metal that contains the dissimilar elements can be approximately considered to be the 3D shape of the molten pool. In the present study, 2205 duplex stainless steel is selected as the dissimilar metal, and a test for detecting the 3D shape of a molten pool formed during a fiber laser full penetration welding process is performed on a 5.5-mm-thick low carbon steel plate. The results show that the method designed to detect the 3D shape of molten pool in laser full penetration welding process exhibits good feasibility and reproducibility, and this method can be used to realize the reconstruction of the 3D shape of molten pool in laser full penetration welding process. Welding experiments based on the three-factor and five-level regression orthogonal design are carried out to obtain the ternary quadratic regression equations of the relationships between the welding process parameters (welding power, welding speed, and defocusing distance) and the geometric shape parameters of the molten pool (the lengths and widths of the top, middle, and bottom sections of the molten pool). The significance of the regression equations is then tested. The effect of each process parameter on the 3D shape of the molten pool formed in laser full penetration welding process is discussed based on the regression equation.

Evaluation of the Radiation Resistance and Thermal Stability of 15KH2MFA-A, Modifications a and B, Steel and Weld-Seam Metal

A comparative evaluation is made of the thermal stability and radiation resistance of VVER-1000 vessel materials and new compositions of 15Kh2MFA-A steel of modifications A and B with low nickel content 0.2–0.8%. For this, complex structural studies and mechanical tests were performed on samples of materials in the following states: the initial state; after isothermal soaking at 330°C up to 7500 h, provoking grainboundary embrittlement of heat treatment in the interval of maximum development of reversible temper brittleness; and, accelerated irradiation to fluence corresponding to the service life of a reactor vessel to 60 or more years. The advantages of reducing the nickel content of steel with the new compositions, which is expressed in their improved radiation resistance and thermal stability, are shown.

MICROSTRUCTURE AND MECHANICAL PROPERTY OF LASER WELDED JOINT FOR HYPOEUTECTOID U-Nb ALLOY

The microstructures and mechanical properties of hypoeutectoid U- Nb alloy laser welded joint were investigated by optical microscopy(OM), X- ray diffractometer(XRD), transmission electron microscopy(TEM), split hopkinson pressure bar(SHPB) and other analysis apparatus. The results show that the microstructure of hypoeutectoid U-Nb alloy base metal is α-U+γ-U lamellar pearlite under isothermal heat treatment, while the laser welding seam is composed of α' lath martensite for pre-heated or α' twin martensite for no pre-heated with orthogonal crystal structure. The quasi-static tensile strength of welded joint(about 400 MPa) is much less than base metal and microstructures of weld, for the main reason of incomplete penetration weld and low fracture toughness. Between dynamic impact loading for base and welded joint, the strain rate of welded joint is lower than base metal, and the yield strength of welded joint is higher. Also, the compressive stress-strain curves indicated that the flow stresses for welded joint increased with the increase of strain rate and the obvious effect of strain rate hardening has been observed. At strain rate of 2000 s-1, selected plastic deformation taking place in welded joint is due to the tremendous difference mechanic properties between weld seam and base metal, and the adiabatic shear band(ASB) only appears in the rest of welded joint.

Experimental assessment of the effectiveness of recovery annealing of VVER-1000 vessels

An experimental assessment of the effectiveness of recovery annealing of VVER-1000 vessels on the basis of mechanical tests and structural studies of control samples of the main metal and the weld-seam metal with high nickel content (>1.65%) in the No. 1 unit of the Balakovo nuclear power plant in states after primary irradiation in the control sample channels, annealing in a chosen regime, and repeat accelerated irradiation in the IR-8 research reactor to fluence corresponding to extended service to 60 yr and longer is presented. The mechanical tests and structural studies showed a high degree of recovery of the structure and properties for the chosen temperature–time regime of annealing as well as a lower rate of repeated after the recovery annealing embrittlement as compared with the rate of embrittlement with primary irradiation.

Investigation of the Beltline Welding Seam and Base Metal of the Greifswald WWER-440 Unit 1 Reactor Pressure Vessel

Abstract The investigation of reactor pressure vessel (RPV) materials from decommissioned nuclear power plants (NPPs) offers the unique opportunity to scrutinize the irradiation behavior under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterization. The paper describes the investigation of trepans taken from the decommissioned WWER-440 first generation RPVs of the Greifswald NPP. Those RPVs represent different material conditions such as irradiated (I); irradiated and recovery annealed (IA); and irradiated, recovery annealed, and re-irradiated (IAI). The working program is focused on the characterization of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the American Society for Testing of Materials (ASTM) Test Standard E1921–08 to determine the fracture toughness of the RPV steel in different thickness locations. In a first step, the trepans taken from the RPV Greifswald unit 1 containing the X-butt multilayer submerged welding seam and from base metal ring 0.3.1 both located in the beltline region were investigated. Unit 1 represents the IAI condition. It is shown that the master curve (MC) approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behavior. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on subsize Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy-V transition temperature TT41J estimated with results of subsize specimens after the recovery annealing was confirmed by the testing of standard Charpy-V-notch specimens. The evaluated TT41J shows a better accordance with the irradiation fluence along the wall thickness than the master curve reference temperature T0. The evaluated T0 from the trepan of base metal ring 0.3.1 varies through the thickness of the RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The re-embrittlement during two campaign operations can be assumed to be low for the weld and base metal.

Reduced activation Fe-Cr-Mn austenitic steels for nuclear power plants

The structure and mechanical properties of candidate materials for nuclear power plants, namely, reduced activation chromium-manganese steels, grade Cr12Mn20W, are investigated, including mechanical properties of weld joints and seams just after the welding process and after additional aging at 400 and 600°C. The investigated steels are characterized by high values of strength properties irrespective of the carbon content. The ultimate strength and yield stress of the weld seam metal are higher than the respective properties of the weld joint. Destruction of nearly all samples arranged with weld joints occurs in the parent metal. Extended holding at the temperature of 400°C for 5000 h actually does not affect the mechanical properties and does not result in a decrease in the material ductility irrespective of the carbon content. Holding at 600°C for over 100 h results in a decrease in elasticity of both the parent metal and the weld joint. Carbides of M23C6 type are evolved in aging, mainly at the grain boundaries. Formation of σ-phase was not observed in the aged samples. The tendency of the steels to form hot cracks upon welding is significantly decreased when the carbon content is decreased. The best combination of strength and elasticity, esspecially at low temperatures, is observed for steel, grade 10Cr12Mn20W.

Nonuniformity of the ductility of 15X2HMΦA low-alloy steel

Irradiation of low-alloy steel used for the manufacture of nuclear-reactor housings poses the risk of reducing its plasticity and shifting the transition from ductile failure to brittle failure to markedly higher temperatures [1, 2]. The embrittlement of reactor housings will largely depend on the content of phosphorus, copper, and nickel in the steel [3‐5]. The resistance to embrittlement is specified by the structure and hence the grade composition of the steel. It depends on factors such as the position of the nonmetallic inclusions, small impurities, and structural inhomogeneity. These factors have not been adequately studied for steel used in reactor housings [6]. Estimation of their contribution to failure may provide useful information for the verification of models and refinement of mechanisms of radiation embrittlement; the prediction of the remaining operational life of reactor housings; identification of effective reduction conditions for housings with short radiation life; and improvement in the production technology for such materials [5, 7]. The housings of the water‐water reactors installed at most nuclear power plants are generally made from 15X2M iA steel (VVER-440 reactors) and 15X2HM iA steel (second-generation VVER-1000 reactors) [5]. In the present work, we investigate the ductility of 15X2HM iA steel and the weld-seam metal for the given technology; the composition of these metals is summarized in the table. After standard heat treatment, some of the Charpy samples (from the basic metal and the weld seam) are subjected to additional (reducing [5]) annealing, in the temperature range corresponding to the development of reversible tempering brittleness. Impact tests (with a Roell Amsler RKP-450) pile driver in the range 20‐100 ° C are accompanied by ductile failure both after initial heat treatment and after reductive annealing. However, the spread of the work of destruction is relatively large: 178‐240 J for the basic metal; and 86‐159 J for the weld seam. Such nonuniformity of the ductility is usually a consequence not only of an increased content of nonmetallic inclusions but also of their wide dimensional range and nonuniform distribution within the metal [6].

Low Energy Welding Technology in Bonding Steel with Aluminum

In welding steel with aluminum, the intermetallic compound of Fe and Al will appear, which will decrease the tenacity, increase the hardness, and lead to a bad joint performance. A new kind of low energy input (LEI) welding technology is introduced and it can be used to weld steel with aluminum by using 4047 wire. The whole welding process is a circulation process of "arcing-short circuit", in which the heat input is reduced greatly. By using this technology, brazing is located on the steel side and arc fusion welding on the aluminum side. From the metallic phase and scanning electron microscope, a continuous and compact intermetallic compound layer with a thickness of 3～4 μm can be observed, which forms in the interface region of the welding seam metal and the galvanized sheet. The main components in the layer are Fe2Al5 and FeAl3, without Zn. Tensile strength tests prove that the joint breaks in the heat affect zone, and the strength is higher than 70% that of the aluminum alloy base material. So, LEI can lead to a good performance joint.

Influence of low-frequency treatment on the mechanical properties and internal stress of weld-seam metal in structural steel

531 The further development of manufacturing calls for energy-saving production technology at each stage of the process. One of the most energy-intensive procedures is heat treatment of large welded structures—in particular, high-temperature tempering to remove residual stress. At OAO GOZ Obukhovskii Zavod, high-temperature tempering of welded structures has been replaced by low-frequency vibrational treatment. Low-frequency treatment is applied to large (length up to 12 m, width up to 4 m) welded 09 E2e and 10 iecN steel structures operating at ambient temperatures between –60 and +50 ° C in considerable (up to 98%) humidity at high dynamic loads. The previous high-temperature tempering included the following operations: placing the billet in the furnace at a temperature no higher than 200 ° C; heating to 510–540 ° C at a rate no greater than 50 ° C/h; temperature equalization and holding (depending on the cross-sectional area and mass of the part); and cooling to 200 ° C at a rate no greater than 50 ° C/h, with final air cooling. High-temperature tempering is a prolonged, energy-intensive process that requires special large furnaces and associated equipment.

Strength of a weld-seam metal and glass-enamel coating composite under conditions of cyclical creep

In the temperature interval 293–573 K we have experimentally established the relationship of the failure stress of a coating (UES 300 with a base sublayer of brand 3132) in a weld-seam metal (Sv08GA steel) composite with a glass-enamel coating under conditions of cyclical creep at levels of up to ttest=6.105 sec. It was noted that below 448 K the failure stress of the coating over the metal of the weld seam is lower by 50–60 MN/m2 than in a composite with a base layer of a hot-rolled thick-sheeted 08GT-brand steel exhibiting greater ductility in tests of short duration, but under identical temperature conditions. The derived results are explained by the appearance within the weld-seam metal in contact with the coating of additional local stresses generated by volumetric changes within the process of residual austenite decay.

Structural characteristics of welded pipe of steel 12Kh18N10T

1. The microstructural mechanism of the development of plastic deformation in the weld seam and base metal are identical. At small deformations the deformation occurs by intragranular slip, and with increasing deformations by additional slip along grain boundaries. 2. The intergranular mechanism of deformation is stronger in the weld seam than in the base metal, as the result of which the first microcracks and then intercrystalline fracture of the metal occur in the weld seam. 3. Analysis of the mechanism of plastic deformation of welded pipe from the type of strain microrelief makes it possible to determine fairly accurately the deformability of the steel and its tendency to intergranular fracture, which should be taken into consideration in determining the maximum deformation of the pipe.

Tensile strength and thermophysical characteristics of weld seam metal in heat-resistant Cr?Ni alloys

Tensile strength and thermophysical characteristics of weld seam metal in heat-resistant Cr?Ni alloys

Corrosion of materials for apparatus used in the production of organic synthetic dyes

1. The weld seams of 1Kh18N9T, Kh18N12M2T, Kh18N12M3T steels have a biphase austenitic-ferrite structure and are subject to selective corrosion around the \gd-ferrite in media used for the production of maleic anhydride. The weld seams of OKh23N28M3D3T steel have a purely austenitic structure and are subject to very slight general corrosion in this medium. 2. OKh21N5T steel and weld seams in this steel undergo insignificant general corrosion in media used for wet recovery of waste gases in the production of phthalic anhydride, but separate deep corrosion pits occur in the weld seam metal. Shallow pitting corrosion occurs in welded 1Kh18N9T steel. Stainless steels containing molybdenum (Kh18N12M2T and OKh21N6M2T) and their weld seams are subject neither to general nor to pitting corrosion. 3. Technically pure VT1-1 titanium is corrosion resistant in media used for the production of isatin by precipitation with hydrochloric acid. When isatin is precipitated with sulfuric acid then OKh23N28M3D3T steel should be used. 4. Weld seams of Kh18N12M2T and OKh21N6M2T steels have a biphase structure (\gg+\gd); they undergo accelerated corrosion in the austenite matrix in the media used for the production of 3-amine-5-sulfosalicilic acid. 5. OKh23N28M3D3T steel with residual stresses induced by forming, welding, and other technological processes undergoes transcrystalline corrosion cracking in media used for the production of benzanthrone.