Welded Structures Research Articles

APPLICATION POSSIBILITIES OF THE S960 STEEL IN UNDERWATER WELDED STRUCTURES

In this paper, the application possibilities of the ultra-high strength (UHSS) Domex 960 steel in the underwater welded structures are analyzed. In the research, the investigated material has been tested in bead-on-plate wet welding conditions with the usage of different heat input values, namely 0.63 kJ/mm, 0.72 kJ/mm and 0.93 kJ/mm. Specimens were performed by the manual metal arc (MMA) welding method with the usage of rutile covered electrodes. Firstly, the nondestructive visual testing (VT) was carried out. In the next step, the metallographic macro- and microscopic tests were performed. Finally, the hardness of the weld metal and heat-affected zone (HAZ) was measured by the Vickers HV10 method. The performed experiments allow the statement that the Domex 960 steel could be welded in a water environment. It also showed that increasing heat input leads to decreasing the hardness in HAZ by 30 HV10. It may result in decreasing the susceptibility to cold cracking during butt- and filet welding in the water environment.

Hot spot stress and fatigue strength assessment of marine 5059 aluminum alloy reinforced structure considering welding effect

AbstractWith the increasing demand for lightweight ships, marine alloy materials such as aluminum alloy and titanium alloy are widely used; 5059 aluminum alloy is considered as an ideal steel for hull structure because of its good mechanical properties and corrosion resistance. The influence of welding residual stress and welding deformation must be considered in fatigue evaluation of thin‐plate welded structures. However, due to the more complex welding deformation and residual stress distribution of thin‐plate welded structures, the fatigue evaluation of thin‐plate welded structures is challenged. In this paper, a series of fatigue tests of actual reinforced T‐shaped welded joints are carried out, and the accurate welding deformation and residual stress are obtained by numerical simulation. Finally, taking welding deformation and residual stress as initial conditions, the hot spot stress S‐N curves of typical joints are modified by hot spot stress method.

Study on Grain Boundary Sensitization in Heat Affected Zone of Austenitic Stainless Steel and its Evaluation Method

In this paper, the simulated welding structure at different areas of heat affected zone (HAZ) of austenitic stainless steel are prepared by heating furnace, and the deference of intergranular corrosion resistance of all samples were determined by comparative methods of oxalic acid etching, hot-acid test and electrochemical potentiodynamic reactivation tests (EPR), and the effectiveness of all those methods were analysis and determination at the same time. The result shows that the susceptibility degree at different areas of HAZ increased with the heating temperature increase, but all structures can pass hot-acid test and EPR test, indicating that it could maintain good performance of intergranular corrosion resistance. The hot-acid test results have good consistency with EPR test , but inconsistent with oxalic acid etching test. The results show that the evaluation of oxalic acid etching is too much strict to be used as a judgment method, so that not suitable of use for inspection.

Study on Corrosion Tendency Evaluation of Microstructure in Welding Heat Affected Zone of Austenitic Stainless Steel

In this paper, the simulated welding structure in different area of heat affected zone (HAZ) of S30408 austenitic stainless steel are prepared, and the corrosion resistance properties are evaluated by electrochemistry method and micro-morphology analysis. The result shows that the corrosion resistance of different areas of the HAZ presents different performance, and the corrosion resistance of the area with the highest heating temperature of 1000-1100 °C is slightly lower than that of other areas.The micro-morphology shows that the pitting of the simulated structure in the HAZ have a certain orientation. The rapid cooling process at high temperature is conducive to the uniform distribution of alloying elements, and it can increase the pitting corrosion resistance of the raw material.

Study on Corrosion Behavior of Simulated Welding Microstructure of Austenitic Stainless Steel

In this paper, the simulated welding structure of austenitic stainless steel is prepared by external heating, and the corrosion resistance of austenitic stainless steel in different areas of heat affected zone (HAZ) is evaluated by means of metallographic structure analysis, electrochemical impedance spectroscopy (EIS) test and equivalent circuit numerical fitting analysis. The result shows that the simulated welding structure of austenitic stainless steel had a growth trend with the increase of heating temperature, but the growth trend is not very obvious. The short thermal process has insufficient driving force for the growth of single-phase austenitic structure. The resulting of product resistance and charge transfer resistance of simulated welding microstructure of austenitic stainless steel is not completely consistent. The simulated welding microstructure of stainless steel shows the tendency of corrosion resistance degradation with the heating temperature increasing, and it has slightly lower when the maximum heating temperature locating at 1000-1100 °C.

Feasibility of early fatigue damage evaluation using the Neutron diffraction method

One of the most successful applications of the Neutron Diffraction (ND) method is the evaluation of residual stress, specifically in welded structures, and many examples exists in the literature. The present study explores the feasibility of applying the ND method to the evaluation of early high-cycle fatigue damage (i.e. the damage prior to formation of fatigue micro- or macro-cracks). In metals and advanced alloys early fatigue damage is normally associated with the accumulation of irreversible and highly localised micro-plastic strains. These strains change the micro-strain/stress field on various scale levels. In this study we attempt to measure these changes applying the ND method to G350 steel fatigue samples, which have been relieved from residual stress and subjected to various degrees of high-cycle fatigue damage. Multiple measurements of the strain/stress field in each sample have been undertaken using the ND method with an incoming beam of 0.5×0.5 mm2. The outcomes demonstrate that it is feasible to evaluate severe fatigue damage using the ND method, and, in general, the severity of the fatigue damage correlates relatively well with the averaged hydrostatic component of the residual stresses measured by the ND. However, more accurate evaluation may require higher spatial resolution (smaller gauge length) and, possibly, a larger number of measurement points to improve the quality of the experimental data.

Development of analysis method for hot cracking considering mechanical and metallurgical factors

Since welding hot cracking is one of the most harmful defects which may largely reduce the strength of welded joints and structures, it is very important to study the prediction and prevention of its generation. Hot cracking is caused by both mechanical and metallurgical factors. In this research, authors proposed a new computational method for evaluating the occurrence of hot cracking through considering both mechanical and metallurgical behavior. As the metallurgical behavior, strain due to solidification shrinkage and mechanical resistance of molten metal were modelled using the solidification ratio as a parameter. The mechanical behavior, an index for generation of hot cracking using the increment of plastic strain is proposed. In addition, authors proposed a simplified prediction method using the temperature gradient for the direction of columnar crystal growth, which affects the location of hot cracking, and is used to evaluate the associate angle of the columnar crystals. The developed method was applied to butt welding. Through the computation using proposed method, it was found that the predicted direction of columnar crystal growth by the proposed method is in good agreement with the experimental results. In addition, the generation of hot cracking in the same butt welding was predicted using the proposed method and the obtained cracking positions agreed well with those observed by experiment. The Influence of the strain of solidification shrinkage on hot cracking was investigated in relation to the surrounding constraints, the temperature gradient and solidification mode, which are presumed to be highly related to the occurrence of hot cracking. From the above results, it can be concluded that the proposed method can analyze the effects of mechanical and metallurgical factors on hot cracking.

Structure, defect substructure and fracture surface of low-carbon alloy steel welds

By the methods of scanning and transmission electron microscopy a structural phase state, defect substructure and fracture surface of low carbon alloy steel welds produced with use of carbon-containing addition and without it are investigated. The study of etched metallographic section structure of welds revealed a presence of a large amount of second phase particles (carbides, sulfides, oxides, etc.). It is shown that in weld with a carbon-containing addition the particles locate chaotically, and in weld without addition they decorate boundaries of ferrite grains. Dimensions of second phase particles vary in the limits from 0.8 μm to 5 μm and are identical for both types of welds. Analysis of fracture surface structure of welds is carried out. A presence of nonmetallic inclusions is detected. They are typical of mainly weld produced without a carbon-containing addition which may indicate its increased brittleness. Amount of micropores in fracture of weld with carbon-containing addition is many times greater than that in weld without addition, which is indicative of gas removal in use of carbon-containing addition. The quantitative analysis of structure and dislocation substructure parameters of weld metal is carried out, the estimates of contributions of scalar and excess dislocation density to strength of welds are performed. It is shown that higher values of scalar and excess dislocation density in the weld formed without carbon-containing addition in flux may be responsible for material embrittlement. A large quantity of stress concentrators in the weld without carbon-containing addition may result in material embrittlement.

A Review on Cold Cracking Phenomenon in High Strength Steel Welded Joints (Causes and Cures)

Welding engineering becomes essentially important in all fabricating branches, such as; oil pipelines, ship industry, oil platforms, vehicle industry, oil tanks, and more applications. Hydrogen-induced cracking related to welding could be a source of genuine harm to welded structures. In this manner, it may be a common topic in such areas and its avoidance is an imperative issue. Steel weldability, with respect to cold cracking, is relative to steel hardenability, which indicates the forming of hard and fragile martensitic microstructure. The most perfect way to dodge martensite is by abating the cooling rate of the parent metal and warming the heat-affected zone. There are numerous arrangements to avoid the over issue, two of them are: preheating and the utilization of fewer hydrogen consumables. The current paper surveys a few of past and later inquiries that are coordinated towards getting a more coherent understanding of the impact of welding parameters on cold breaking shirking, centering especially on the impact of preheating technique and diffusible hydrogen levels on cold cracks of different steel types. However, one of the foremost vital discoveries of this ponder is that resistance to hydrogen-induced cracks has for the most part progressed in numerous steel types, and the required ways to dodge cold cracks by control of the welding conditions are well set up.

PERFORMANCE CHARACTERISTICS OF NICKEL-CONTAINING STEEL STRUCTURES DURING MECHANIZED WELDING-SURFACING WITH MODIFIED (DOSED) ELECTRODE WIRE FEEDING

Purpose. To study and analyze in a comparative order the influence of factors of the controlled pulse process of electrode wire supply on some basic mechanical characteristics of seams and welded rollers in the processes of welding and surfacing of nickel-containing steels.
 Methods of research. The study the mechanical characteristics of seams and welded rollers was carried out using modern laboratory equipment and appropriate techniques. This made it possible to determine how the pulse feed parameters affect the strength characteristics of the weld and near the weld zone over the entire cross-sectional area of the weld or weld layer. Detailed characteristics of feed pulses were determined using a welding process analyzer to obtain oscillograms of power parameters of arc combustion with their analysis, including determining the stability of the arc process for different types of pulses. Important for the improvement of welding results is the controlled nature of the electrode metal transfer synchronous with the pulsed movement of the electrode. It is noted that the energy consumption of the arc process during the pulse supply of the electrode wire with an indication of its reduction compared to traditional welding.
 Experimental work was performed using a special electrode wire, which is usually used for welding and surfacing of nickel-containing steels. These processes were carried out in a protective environment of CO2 in automatic mode.
 Results. Due to the fact that the strength characteristics of the weld are among the most important, attention is paid to their definition and analysis. The strength characteristics depend on many parameters, in particular the thermal characteristics of the process, the structure of the weld metal, the presence of non-metallic inclusions and so on. All these factors were studied with the help of appropriate instruments, and on the basis of numerous comparative photos of microstructures on sections of the cross section. The analysis of the sections revealed the types of microstructures obtained, the presence of inclusions and more. It is determined, in particular, that the structure of weld metal in pulsed electrode wire welding differs significantly from the structure of traditional welding in reducing inclusions, finer grains, etc., which improves the mechanical properties of the weld and seam area.
 Scientific novelty. Based on a series of experimental studies, the use of pulse algorithms for the movement of the electrode wire with certain parameters in automatic mode for welding and surfacing of nickel-containing steels to improve the mechanical properties of seams and welded rollers.
 Practical value. It is determined that the method of pulse welding of electrode wire to the controlled variant, including nickel-containing steels is effective and can be widely used in industry using specially designed equipment that provides a suitable process with stronger characteristics.

A strength estimation method for aluminum alloy butt welded joints with mismatched mechanical properties

Aluminum alloy thin-walled welded structures have been widely used in automotive lightweight design. However, during the welding process of aluminum alloy sheets, the mismatched welded joints with different microstructure and mechanical properties are formed. The entire mismatched welded joint can be divided into four zones, including welded zone (WZ), hardening heat affected zone (HZ), softening heat affected zone (SZ) and base metal zone (BM). This study aims to analyze the effects of mechanical properties and geometrical characteristics of different welding zones on the load-bearing capacity of aluminum alloy thin-wall welded structures. According to experimental results, the relationship between hardness and ultimate tensile strength was investigated. And then, a tetra-material model of mismatched welded joints was established based on the hardness distribution, and the strength of mismatched welded joints was systematically investigated by numerical simulation. Additionally, the statistical analysis of the relationship between mismatched parameters and the strength of welded joints was conducted through the design of experiments (DOE). The results show that the existence of SZ exerts a crucial role in the loading capacity of the welded joint. The main effects and interactions of geometrical and mechanical properties parameters have a great influence on the load-bearing capacity of welded joints. Moreover, the proposed meta-models could effectively predict the strength of thin-wall welded structures, providing a guideline for evaluating the load-bearing capacity of the complex components with the welded structures.

Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Causes of damage occurrence in vital components of welded structures of the bucket-wheel excavator boom (DU1) at the coal landfill of the thermal power plant 'Nikola Tesla A' in Obrenovac (Serbia) are investigated. Bucket-wheel excavator was produced by French company 'Ameco' and it moves along the circular track. Taking into account lack of technical documentation, all tests and were carried out under the assumption that welded structures were made of structural steels S355 and S235. Investigation of causes of damage occurrence are based on results of non-destructive tests (NDT) and tensometric measurements.

Evaluation of local stress‐based fatigue strength assessment methods for cover plates and T‐joints subjected to axial and bending loading

AbstractThis study aims to find suitable fatigue assessment methods for welded structures (cover plates and T‐joints) subjected to axial and bending loading. The Hot Spot Stress (HSS), 1‐mm stress (OM), Theory of Critical Distances (TCD), Stress Averaging (SA), and Effective Notch Stress (ENS) methods are evaluated in terms of accuracy and reliability. The evaluation is based on fatigue test data extracted from the literature and carried out in this study. It is found that the SA method can be used to assess the fatigue strength of cover plate joints under axial loading with relatively good accuracy and low scatter, followed by the ENS method. The HSS, TCD, SA, and ENS methods are conservative estimation methods for T‐joints under bending, while the accuracy is low. Furthermore, fatigue design curves applicable for T‐joints under bending are discussed, which can be used in the TCD method and SA method.

Comparative analysis of methods for reducing residual stresses in welded structures made of austenitic steels

In this article, the authors conducted a comparative analysis of methods for removing residual stresses in welded structures. The reasons for the formation of residual stresses and methods of their removal are given.

Spot Weld Inspections Using Active Thermography

Spot welds have a significant part in the creation of automotive vehicles. Since the integrity of, for example, a car, is dependent on the performance of multiple welds, it is important to ensure the quality of each spot weld. Several attempts have been made in order to determine the quality of spot welds, but most of them do not focus on the applicability in the manufacturing process. Spot weld inspections are often performed using back heating. However, during manufacturing, robotic inspections are desired, and since the bodywork of a car is a complex shape, the accessibility from the inside of the vehicle is minor. Therefore, inspections using front heating are more suitable. In this manuscript, multiple excitation methods are compared as well as different post-processing techniques. The used excitation techniques can be divided into light heating and inductive heating. Light heating is further divided in lock-in thermography and pulse thermography. The used post-processing techniques are principle component analysis and fast Fourier transform. Inductive heating turns out to be the most suitable measurement technique since it is fast and can be performed as front and back heating. Both investigated post-processing techniques deliver suitable information, such as relief images and information of the internal structure of the spot weld.

On the Accurate Prediction of Residual Stress in a Three-Pass Slot Nickel-Base Repair Weld by Numerical Simulations

The activities within a European network to develop accurate experimental and numerical methods to assess residual stresses in structural weldments are reported. The NeT Task Group 6 or NeT-TG6 project examined an Alloy 600 plate containing a three-pass slot weld made with Alloy 82 consumables. A number of identical specimens were fabricated and detailed records of the manufacturing history were kept. Parallel measurement and simulation round robins were performed. Residual stresses were measured using neutron diffraction via five different instruments. The acquired database is large enough to generate reliable mean profiles, to identify clear outliers, and to establish the systematic uncertainty associated with this non-destructive technique. NeT-TG6 gives a valuable insight into the real-world variability of diffraction-based residual stress measurements, and forms a reliable foundation against which to benchmark other measurement methods. The mean measured profiles were used to validate the accuracy achieved by the network in the prediction of residual stresses.

Fatigue life prediction of gasoline storage tank considering varying current density and weld stress

In the field of corrosion fatigue crack research, how to couple corrosion and fatigue under various conditions is a problem worthy of discussion. According to the electrochemical corrosion principles and the superposition principles, studies have been made on the interaction between corrosion and fatigue, and the relationship model between the corrosion fatigue crack size and the corrosion fatigue remaining life in the Corrosion of Hydrogen evolution (COHE) fatigue long crack growth stage is established. The feasibility of the model is verified by using the experimental data. According to the specific structure of the dislocation butt weld of large storage tank, the stress at the crack is calculated. Based on the above model and the experimental data, the corrosion fatigue residual life of large storage tank is predicted. The feasibility of the model is verified, which provides a new method for corrosion fatigue life prediction of large storage tanks.

Fine Structure and Fracture Surface of Low-Carbon Steel Welds

Fine Structure and Fracture Surface of Low-Carbon Steel Welds

Micro-crystallographically unraveling strength-enhanced behaviors of the heavy-thick Ti-6Al-4V welded joint

Developing high-strength welded joint of heavy-thick titanium alloy plates is in immediate need to unravel the strength-enhanced behaviors for high-pressure and low-temperature performance of deep-sea submersibles. Here, we synergistically employed transmission electron microscope (TEM) and electron back-scattered diffraction (EBSD) technologies to micro-crystallographically unravel the evolution behaviors of weld microstructure, grain orientation and grain boundaries for the welded joint of the heavy-thick Ti-6Al-4V plates with the thickness of up to 60 mm. Resulted, the strength-enhanced welded joint was evidently ascribed to the transformation of lath martensite into basketweave-martensite and the rigid-flexible mixture strategy of the enhanced conical-texture and the weakened basal-texture and cylindrical-texture. Furthermore, the remarkably lowered geometrically necessary dislocations (GNDs) density and the greatly decreased deformation-prone grains number due to the transformation of low-into-high angle grain boundaries indispensably strengthened the joint strength. Therefore, this work has made clear the strength-enhanced behaviors of Ti-6Al-4V welded joints for substantially improving high-strength welded structure of heavy-thick titanium alloy plates, and sufficiently promoting the service safety for deep-sea submersibles. • Transformation of lath martensite into basketweave-martensite enhanced the welded joint strength. • Thermal cycling caused the rigid-flexible mixture of the enhanced conical-texture and the weakened basal-texture. • Transformation of low-into-high angle grain boundaries lowered GNDs density and decreased deformation-prone grains number.

Influence of pulsed-arc welding modes on the structure and mechanical properties of welds and haz metal of welded joints of 30Kh2N2MDF steel

The Paton Welding Journal, 2022, №05. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.