Welded Steel Joints Research Articles

APPLICATION OF ACOUSTIC EMISSION METHOD FOR DETECTING DIFFUSION INTERLAYERS IN DIFFERENT WELDED JOINTS

The paper investigates the possibility of detecting specific structural defects of dissimilar welded joints by the method of acoustic emission (AE). Carbide and decarburized interlayers are formed in dissimilar welded joints of austenitic and pearlitic steels during welding and subsequent operation. Diffusion interlayers, as a structural defect, are usually small in size and cannot be detected by traditional non-destructive testing (NDT) methods, while the AE method is promising for detecting such defects. In the present work, we studied the AE data obtained during testing of defect-free specimens of a welded joint and specimens with diffusion interlayers. It has been established that the AE parameters for defective and defect-free welded joints have significant differences, which makes it possible to identify the presence of diffusion interlayers in dissimilar welded joints.

Effect of cyclic waveforms on cavitation propensity of P91 steel weld joint at 873 K

Effect of cyclic waveforms on cavitation propensity of P91 steel weld joint at 873 K

Microstructures and Creep Properties of Type 316LN Stainless Steel Weld Joints

Microstructures and Creep Properties of Type 316LN Stainless Steel Weld Joints

Structure and properties of welded joints of 06G2BDP steel

Structure and properties of welded joints of 06G2BDP steel

Структура і властивості зварних з’єднань сталі 06Г2БДП

Структура і властивості зварних з’єднань сталі 06Г2БДП

The effect of vanadium micro-alloying on the microstructure of welded joints in high-strength structural steels

The balance between high strength and toughness in high-strength-low-alloy (HSLA) steels can be defined by the thermal cycles in the heat-affected zone (HAZ) of a welded joint, during a double-pass welding process with secondary heating in the inter-critical zone (IC CG HAZ). After multiple heating cycles in the temperature range between Ac1 and Ac3, the steel undergoes a strong loss of toughness and resistance to fatigue, mainly caused by the formation of residual austenite (RA). This study aims to investigate the influence of vanadium addition on the behavior of IC GC HAZ in S355-grade HSLA steel. The welding thermal cycles were simulated, considering five different inter-critical temperatures, between 720 and 790 °C. The addition of vanadium as a micro-alloy to an S355 structural steel was found to increase the mechanical strength of the IC GC HAZ zone of a welded joint without compromising toughness and fatigue resistance. This result is obtained through the generation of a bainitic microstructure with dispersion of fine regions of residual austenite and a fine and uniformly distributed precipitation.Graphical abstract

Microstructural characterization of welded plates of austenitic low-density Fe-Mn-Al-C steels microalloyed with Ti/B and Ce/La

The excellent combination of tensile strength and elongation of low-density (LD) steels of the Fe-Mn-Al-C system has generated great interest in the metallurgical field. The need to understand the effects produced by welding processes has increased the studies carried out on the weldability of LD steels. Researchers have focused their attention on the weldability issues of LD steels, which occur due to the high Mn, Al, and C contents and their harmful effects in welded joints, such as segregation, hot cracking, and phase transformations, which, in turn, may decrease mechanical resistance. The main objective of this research work is to study the microstructural and mechanical behavior of the fusion zone (FZ) and different heat-affected zones (HAZs) generated by the welding of Fe-31Mn-8Al-1.9 C, Fe-31Mn-8Al-1.9C-Ce/La, and Fe-27Mn-7Al-1.2C-Ti/B austenitic LD steels in 3.5 mm thickness plates through an autogenous GTAW process. The welded plates were mechanically, metallographicaly, and structurally characterized by means of Vickers microhardness (HV), light optical microscopy (LOM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results exhibited strong variations in the microhardness profile of the welded joint, particularly in the heat-affected zones. The lowest hardness values (≈ 250 HV) were found in the FZ, which was associated with the dendritic structure. The HAZ-1 near to the FZ showed hardness values in the range of 300–375 HV, whereas HAZ-2 furthest from the FZ showed the highest hardness values (up to 430 HV), which could be associated with moderate and high κ-carbide precipitation with modulated structure, respectively. The welded joints of the LD steels under study did not exhibit cracking and showed austenite as the main phase, as well as low presence of α-ferrite, κ-carbides, and β-Mn.

The Effects of Post-Weld Heat Treatment on the Microstructure and Mechanical Properties of 9% Ni Steel Weld Joint with Fe-Based Filler Material

A Fe-based filler material with the composition of Fe-20Ni-5Co-2.5Mn-0.2C was used for welding 9% Ni steel, and the effect of post-weld heat treatment on the microstructure and mechanical properties of the welded joints was investigated. Post-weld heat treatment of the welded joint was performed in the temperature range of 200 to 600 ℃. After the experimental selection, the microstructure changes of the weld metal and base metal were investigated in detail at heat treatment temperatures of 350 and 600 ℃. Grain morphology, size, and the location of precipitated cementite were studied using SEM and EBSD phase maps. The mechanical properties of the weld joint were characterized by tensile properties and micro-hardness. Based on the experimental results, this study provides key insights into the applicability of post-weld heat treatment to weld joints of 9% Ni steel prepared using Fe-based filler material to improve the mechanical properties, toughness and ductility of the weld joints.

Comparative study of microstructure and toughness of automatic welded joints of X70 pipeline steel with no slope and 25° slope

X70 pipeline steel is the most widely used for oil and gas pipeline transportation. When it is used in mountainous areas, the probability of pipeline failure increases dramatically due to the lack of toughness of welded joints. In order to ensure the welding quality, fully automatic welding has become the trend of pipeline welding. In this paper, X70 pipeline steel is butt welded by fully automatic welding under the condition of both no slope and 25° slope, and the microstructure and the toughness of two welded joints were observed and measured. The results show that the slope affects grain size and impact toughness. The grain size of the coarse-grained heat-affected zone (CGHAZ) in the root weld at the lower groove is larger than that at the upper groove. The impact energy of the heat-affected zone (HAZ) at the upper groove is significantly higher than that at the lower groove. For no slope welded joint, the weld CTOD value in the NQ direction is the lowest. For the 25° slope welded joint, the weld CTOD values are lower than HAZ CTOD values. Meanwhile, the HAZ CTOD values in the NP direction are significantly lower than those in the NQ direction. The fracture morphology of impact and CTOD of two welded joints is similar. The root-weld CGHAZ at the lower groove is the weakest area in the welded joint. For welding under slope conditions, the effect of slope on the performance of welded joints must be taken seriously.

Microstructure and properties of magnetic field assisted laser wire-filled welded 22MnB5 steel joints

The magnetic field-assisted laser wire-filled welding test of 1.5 mm automotive 22MnB5 steel is performed to investigate the influence of magnetic field on the microstructure and properties of the welded joints. When no magnetic field is applied, and the laser heat input is 190 J mm−1, the welded joint width and the grain size of the coarse grain region are large. Also, there is an obvious hump defect at the bottom of the weld. Under the same heat input conditions, when a 5 mT and 15 mT steady magnetic field is applied, the thermoelectric magnetic force generated by the magnetic field promoted the flow of molten pool and concentrated laser energy. It is found that the hump defect is eliminated, the width of the welded joint is reduced, the grain size of the coarse grain region is significantly reduced, and the overall hardness of the welded joint is improved. However, different magnetic induction intensities have different effects on the solid phase transformation of the weld. When no magnetic field is added, the weld center is mainly composed of granular bainite and polygonal ferrite due to the slow cooling rate of the molten pool. When the applied magnetic field is 5 mT, the center of the weld is mainly composed of brittle and hard upper bainite because the thermoelectric magnetic force stirs the molten pool and accelerates the cooling rate of the molten pool but the overall mechanical properties of the welded joint were relatively poor. At 15 mT, lath martensite and lower bainite predominate in the weld center due to the increased cooling rate of the molten pool, thereby increasing the overall mechanical properties of the welded joint. Therefore, choosing the appropriate magnetic induction intensity is critical for improving the microstructure and properties of welded joints.

The Influence of Steel Variability on the Reliability of Welded Beam‐to‐Column Joints

AbstractBeam‐to‐column joints have a significant impact on the reliability of load‐bearing steel frame structures. Proper characterisation of the joint behaviour affects the distribution of internal forces and bending moments in frame structural members and affects their reliability level. This article addresses the effect of the variability of steel mechanical properties on the overall behaviour and reliability of welded beam‐to‐column joints. Monte Carlo simulations and parametric numerical analyses were performed to investigate the influence of the variability of mechanical properties on the behaviour (failure modes and resistances) of the joint and to generate data for the reliability analysis. Reliability analyses were performed to calculate partial resistance factors (γM1) for welded steel joints using the procedure given in Annex D of EN 1990. The analyses included the FprEN 1993‐1‐1:2022 and JCSS probabilistic models for mechanical properties of steel and two approaches for determining joint plastic bending resistance. It was concluded that FprEN model gives more favourable values of γM1. It was also found that the approach for determining joint plastic bending resistance can have a large effect on the partial resistance factor γM1 and ultimately on the reliability of the joint.

Towards an advanced fatigue assessment of welded steel joints with multiaxial stress states

AbstractAdvanced fatigue assessment methods, e.g. the Two‐Stage‐Model, are needed for the design of complex constructions or to accurately evaluate the remaining fatigue life of existing structures. The applicability of the Two‐Stage‐Model, including strain‐life approach and linear elastic fracture mechanics, was experimentally validated for uniaxial stress states only. However, typical construction details of steel and composite structures often exhibit a multiaxial non‐proportional stress state, which leads to variable principal stress values and directions. Comprehensive extensions of the Two‐Stage‐Model from uniaxial to multiaxial stress states are missing so far. This paper shows a study on advanced approaches that incorporate multiaxial stress states for both the crack initiation stage and the crack propagation stage, and their application in the Two‐Stage‐Model. For crack initiation, several approaches for the strain‐life approach, including multiaxial non‐proportional hardening and damage assessment based on critical planes are evaluated with respect to an application on the strain‐life approach. For the extension of the crack propagation stage, a computational procedure using XFEM and mixed‐mode approaches is presented.

Influence of Oxygen Content in the Protective Gas on Pitting Corrosion Resistance of a 316L Stainless Steel Weld Joint.

Gas tungsten arc welding (GTAW) is commonly used for joining pipelines; however, it often leads to discoloration in the heat-affected zone (HAZ). In this study, 316L pipes were welded with different concentrations of oxygen present in the argon purge gas during welding. The objective of this study was to investigate the effect of oxygen concentration in the protective gas on the pitting corrosion resistance of welded pipes. The experimental results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas resulted in an increase in pitting corrosion resistance until a critical value, beyond which the resistance decreased. The results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas increased the pitting corrosion resistance until a critical value, beyond which the resistance decreased due to the formation of iron oxide. This study provides valuable insights for improving the corrosion resistance of welded pipes in the oil and gas industry.

Effects of V-N Microalloying on Low-Cycle Fatigue Property in the Welded Joints of Constructional Steel.

Low-cycle fatigue testing was carried out for the welded joints of constructional steels containing 0% V + 0.0021% N and 0.10% V + 0.0078% N, and the effects of V-N microalloying on the low-cycle fatigue property of the welded joints were investigated. The results showed that when the total strain amplitudes were 1.2%, 1.4% and 1.6%, the mean low-cycle fatigue lives of the welded joints of steel containing 0.10% V + 0.0078% N were 5050, 2372 and 1535 cycles, respectively, which were significantly higher than those of the welded joints of steel containing 0% V + 0.0021% N; however, when the total strain amplitudes increased to 1.8% and 2.0%, the mean low-cycle fatigue lives of the welded joints of steel containing 0.10% V + 0.0078% N were 575 and 367 cycles, respectively, which were gradually lower than those of the welded joints of steel containing 0% V + 0.0021% N. The reasons causing the difference of low-cycle fatigue life were explained by the dislocation structure and precipitates in the welding heat-affected zone, plastic strain energy density of the welded joints, and fatigue fracture morphology. When the low-cycle fatigue life is between 100 and 200 cycles, the cyclic toughness of the welded joint of steel containing 0.10% V + 0.0078% N is between 57.48 and 78.22 J/cm3, which is higher than that of the welded joint of steel containing 0% V + 0.0021% N, indicating that the welded joint of steel containing 0.10% V + 0.0078% N is able to absorb more energy in a seismic condition, therefore possessing better seismic resistance.

Determination on the fracture toughness of the welded joints of X80 pipeline steels based on small punch test

For the sake of design and integrity assessment of the fracture toughness of high-grade pipelines, it is necessary to carry out accurate fracture toughness assessment of the welded joints. The study of more concise and effective fracture toughness testing methods has important theoretical and engineering value. At present, the fracture control of girth welding joints is mainly based on J integral, CTOD and CTOA. However, it is hard to carry out standard fracture toughness tests at some local narrow areas of the welded joints such as the heat affected zone for the difficulty of sampling. On this basis, this paper aims to propose a method to determine the fracture initiation toughness JIC of the welded joints of high-grade pipeline steels based on the micro-sample test method - small punch test. Firstly, small punch specimen with through-thickness notch was designed. Secondly, the finite element model of the notched specimen was established, and verified by the notched specimen tests of X80 steel. Furthermore, the elastic–plastic material properties of different zones of the welded joint were obtained by the empirical correlation method of small punch test and further used for the determination of J contour integral. The GTN damage parameters were calibrated by the three-point bending tests and further used for the determination of the crack initiation displacement. Finally, the fracture initiation toughness JIC(SPT) of different zones of the welded joint were obtained by the SPT method and verified by the three-point bending test. The results show that the fracture initiation toughness JIC(SPT) of each region of the welded joint obtained by notched SPT specimen were all less than the SENB test results. But there is a good empirical correlation between the two results so that the SPT method can be further modified by establishing an empirical correlation model. The SPT method has good engineering application prospect for the accurately characterization of the different distribution of fracture toughness in different areas of the welded joints.

Effect of post-welding sensitisation on the degree of sensitisation of the welding zones of AISI 304 resistance spot welding joints studied by using an electrochemical minicell

ABSTRACT In resistance spot welding (RSW) joints of austenitic stainless steel (ASS), a small-scale electrochemical cell (minicell) was used for assessing individually, on each of the three welding zones, of size less than 1000 µm (fusion zone (FZ), heat affected zone (HAZ) and base metal (BM)), the combined effect of a RSW process and post-welding sensitisation on the degree of sensitisation (DOS). The results show that the three welding zones have different microstructures that make each of them respond differently to post-welding sensitisation. The DOS varies with post-welding sensitisation time in all three welding zones, but it varies at a different rate in each welding zone (the highest rate in the FZ). This variation is due to the fact that when the DOS reaches a certain level, which is observed when plotting the reactivation charge (Qr) versus the post-welding sensitisation time, a microstructural regeneration occurs.

Microstructure and Pitting Corrosion Characteristics of Tig Welded Joints of Super 304HCu Austenitic Stainless Steel

Abstract Super 304HCu is an advanced ultra-super critical (A-USC) boiler grade austenitic stainless steel with the distinct addition of 3 wt.-% of Copper. A-USC power plants intended to operate in chloride rich environments (sea shore, feed water residues, etc.) are susceptible to chloride assisted corrosion failures. In this study, the pitting corrosion behaviour of the Super 304HCu parent material and tungsten inert gas weld joints was studied using a potentiodynamic cyclic polarization test in 3.5 % NaCl solution at three different pH levels (pH = 3, pH = 7, and pH = 11). The Epit values of the parent material is found to be much nobler than that of the weld joints. The micrographs of the pitted weld joints and the oxalic acid etched structure of Super 304HCu joints are presented. From the micrographs it is revealed that the heat affected zone is the most susceptible region to pitting corrosion.

Use of laser welding and surfacing technologies for repair and manufacture of thin-walled welded joints of high-alloy steels

Use of laser welding and surfacing technologies for repair and manufacture of thin-walled welded joints of high-alloy steels

Mitigating HAZ softening of friction stir welded ferrite-martensite DP steel followed by post weld heat treatment

This study investigates the development of microstructure and mechanical properties in welded joints of ferrite-martensite DP780 steel, with different cooling pathways applied after post-weld heat treatment (PWHT). The findings suggest that quenching in liquid nitrogen (PWHT-LNQ) effectively mitigates the softening of the heat-affected zone by suppressing the formation of tempered martensite and reducing carbide coarsening. The technique promotes a refined microstructure characterized by the discrete distribution of block martensite within the ferrite islands. This microstructural arrangement significantly enhances the strength and ductility properties of the material. Notably, PWHT-LNQ achieves the highest tensile elongation of 17%, which is approximately 2.2 times that of the as-welded joint.

ВЛИЯНИЕ ТЕРМИЧЕСКОГО ЦИКЛА СВАРКИ НА СТРУКТУРУ И СВОЙСТВА ФЕРРИТО-АУСТЕНИТНЫХ СТАЛЕЙ 08Х22Н6Т И 08Х18Г8Н2Т

The results of researches on influence of thermal cycle of welding on structure and phase transformations in metal of heat-affected zone of welded joints of 08Cr22Ni6Ti and 08Cr18Mn8Ni2Ti steels are presented. It is shown, that at automatic submerged-arc welding of welded joints of ferrite-austenite steels the fall of plasticity is observed. It is established that the impact toughness of overheat section of heat affected zone at normal temperature has high values of impact toughness, and at test temperature of minus 20 oC values of impact toughness below 0.4 MJ/m2 were obtained.