Welded Steel Joints Research Articles

Enhancing the tensile performance of 12Cr17Mn6Ni5N steel weld joints through strengthened grinding process-induced gradient structures

This paper investigates the surface enhancement treatment of 12Cr17Mn6Ni5N steel weld joints using the Strengthened Grinding Process (SGP) and explores its effect on their surface characteristics and tensile performance. The study begins by examining the influence of different SGP durations on the weld joints' surface morphology, microhardness, and residual stress. Subsequently, the tensile properties of the SGP-treated samples are analyzed and the potential mechanisms by which SGP enhances the tensile performance of 12Cr17Mn6Ni5N steel weld joints are discussed. The results reveal that SGP treatment increases the maximum microhardness of 12Cr17Mn6Ni5N steel weld joints to 519.3 HV, marking a 109.9 % improvement as compared to untreated samples. Additionally, the samples’ surface residual stress was changed from residual tensile stress (46.5 MPa) to residual compressive stress (−1253.1 MPa). The SGP-treated samples exhibit a tensile strength of 671.43 MPa, marking an 8.51 % increase as compared to the untreated samples, while also achieving a simultaneous elongation of 16.42 %. The research demonstrates that SGP is an effective method for enhancing the tensile performance of specific mechanical components.

Microstructural characteristics of different heat-affected zones in welded joints of UNS S32304 duplex stainless steel using the GMAW process: analysis of the pitting corrosion resistance

Abstract The influence of specific microstructural characteristics on the properties of single-pass welding joints was assessed by optical processed images, transmission electron microscopy, microhardness measurements and corrosion tests conducted in various regions of the heat-affected zone (HAZ) in a lean duplex stainless steel. The welded joints were obtained with heat inputs of 1.5 and 2.5 kJ/mm using a gas metal arc welding (GMAW) process with a shielding gas enriched in Ar. Three selected regions in the HAZ showed different ferrite grain sizes and austenite fractions. The place in the welded joint where the HAZ was narrowest, and therefore experiences the highest cooling rate, is most prone to the formation of cubic CrN metastable nitrides. Conversely, the place where the HAZ was wider promotes the precipitation of stable Cr2N nitrides with more coalesced intragranular austenite (IGA) particles, where presumably random interfaces predominate. The HAZ region where the cooling rate was the highest presented more pitting corrosion resistance.

Evaluation of welded joints of austenitic stainless steels at high temperatures in the presence of SO2, SO3, and O2

This study undertakes a comprehensive examination of crack formation in welded joints of austenitic stainless steel 304, particularly in high-temperature corrosive environments prevalent in sulfuric acid production units. Initially, an investigation was conducted on a steam superheater that had been operational for about 19 years, where a crack formation was discovered. This unit, subjected to a working temperature of approximately 620 °C and exposure to gases composed of SO2, SO3, and O2, allowed for the analysis of corrosion products formed during the crack propagation. Building on the initial findings, a more controlled study was undertaken, focusing on the cracks formed in welded joints using the coated electrode E308L for joining 304H stainless steel plates under similar corrosive conditions. The specimens, constructed using materials typically utilized in sulfuric acid production units, were designed based on the double-beam principle, enabling exposure to both tensile stresses and a corrosive environment at high temperatures. Over a span of 122 days, or roughly 3000 h, microstructural analyses were conducted, revealing that the formation and propagation of cracks preferentially occurred through fragile microconstituents, notably the sigma phase. These findings mirrored the sigma phase formation observed in the initial superheater study and point to a stress corrosion process acting synergistically with sigma phase development, and consequently seen as a probable cause of failure. This comprehensive evaluation, therefore, indicates a significant role of the sigma phase and corrosive environments in influencing crack formation and propagation in welded joints of austenitic stainless steels, which require further studies for preventative strategies in industrial setups.

Thermal aging effects on Tensile and Metallurgical characteristics of Stainless steel weld joint

A girth austenitic stainless steel (say, SS) weld joints are invariably used for joining piping components in typical light water based nuclear power reactor. To avoid hot cracking during the welding of SS, some 5-8% delta ferrite is required in the filler material, which remains in the metastable phase in weld pool. Under prolonged exposure at operating temperature (300 ℃), these delta ferrite which remains in weld metal may get transformed to brittle phases that leads to reduction in its ductility and toughness. Hence, for prolonged safe operation of these piping components in power reactors, it is important to quantify the amount of degradation in toughness and ductility because of thermal aging. Therefore, present work aims at quantifying the reduction in toughness in SS weld joint by carrying out accelerated thermal ageing and thereafter carrying out micro-structural examinations, hardness and tensile tests on specimens machined from different regions of weld joint. Austenitic stainless steel (SA312 Type 304LN) pipe weld joints have been prepared using Gas Tungsten Arc Welding (GTAW) for root passes and Shielded Metal Arc Welding (SMAW) for filling passes. Full-scale pipe weld were subjected to thermally ageing for 10,000 and 20,000 hours at temperature 400 ℃. The effects of thermal aging on the structural morphology, hardness at macro and micro-scale and tensile characteristics of different zones of these joints have been quantified. Micro-structural examination reveals vermicular and lathy morphology in the ferrite and austenite phase. It has been found that, thermal aging leads to significant increase in ferrite hardness and reduction in ductility for the weld specimen from SMAW compared to that of the GTAW and no effect in heat affected zone.

Application of acoustic emission and digital image correlation for detecting diffusion interlayers in dissimilar welded joints

The paper investigates the possibility of using the acoustic emission (AE) method to detect carbide and decarburized interlayers formed in dissimilar welded joints of austenitic and pearlitic steels during welding and subsequent operation.

Numerical validation of fatigue properties and investigation of local deformation of heat-affected zones in P91 steel’s weld joint

The low cycle fatigue (LCF) behavior of P91 steel weld joint (WJ), prepared by gas tungsten arc welding, has been investigated both experimentally and numerically. However, due to the smaller size and complex geometry of various zones of the WJ, the experimental investigation of the local fatigue behavior of different sub-regions of the heat-affected zones (HAZ) could not be made. Hence, the sub-regions of the WJ were reproduced at bulk scale by physical-thermal simulation (PTS) (i.e., heat treatment) to study the LCF behavior of the individual zones of P91 WJ. In the literature, the accuracy of such physical-thermally simulated bulk-scale specimens, which correspond to different sub-regions in the weld joint, is confirmed by comparing the microstructures and microhardness. In this article, a new method, based on the LCF experiment and finite element simulation, is proposed to validate the PTS method and the fatigue properties of the sub-regions of the weld joint. The simulation accurately predicted the failure location and also the most vulnerable sub-region within the WJ, as observed experimentally. Moreover, significant ratchetting and heterogeneous deformation were observed in the sub-regions of the WJ.

Investigation of the High-Temperature Low-Cycle fatigue failure characteristics of P91 steel weld joints and their fatigue strength reduction factors under various load control regimes

Low cycle fatigue tests are conducted on the base metal, weld metal, a welded joint under the condition that the strain control region is the joint (WJWJ) and a welded joint under the condition that the strain control region is the base metal (WJBM) of P91 steel at 500℃ using different total strain ranges. The cyclic stress response is highest for the weld metal, followed by the base metal, and is relatively similar for WJWJ and WJBM. At 2.0 % total strain range conditions, the materials generally exhibit non-Masing behavior and dynamic strain hardening aging. At all total strain ranges, WJWJ failed in the heat-affected zone, and WJBM broke in the base metal. For the difference in fatigue life between base metal and welded joints, the fatigue strength reduction factor of P91 steel welded joints at 500 °C is given as a suggested value. The fatigue behavior of P91 steel welded joints is verified based on a hybrid hardening model and a modified damage model. This study presents a theoretical framework for analyzing the fatigue strength reduction factors of weldments and comparatively analyzes the effects of different geometrical features.

Enhancement of high-temperature fatigue properties of 310S stainless steel welded joints by strengthened grinding process inducing gradient structure

This study employed the strengthened grinding process (SGP) for surface enhancement treatment of 310S stainless steel weld joints. The surface characteristics and high-temperature fatigue performance were investigated. Initially, the effects of different SGP durations on the surface morphology, microhardness, and residual stress of the weld joints were studied. Subsequently, the high-temperature fatigue life of samples processed through SGP was examined, and the potential mechanisms underlying the impact of SGP on the high-temperature fatigue behaviour of 310S stainless steel weld joints were discussed. The maximum hardness of SGP-6M samples was 337 HV, while the average hardness of UP samples was 163 HV, and the maximum hardness of SGP-6M samples increased by 90.18 % compared to UP samples. The surface residual stress changed from a residual tensile stress of 205.24 MPa to a residual compressive stress of −864.76 MPa. At 25 °C, 500 °C, 600 °C, and 700 °C, the fatigue life increased by 36.9 %, 31.7 %, 25.9 %, and 18.6 %, respectively. This research demonstrates that SGP is an effective method for increasing the high-temperature fatigue life of turbine blades.

Kaynaklı Çelik Birleşimlerin Yorulma Analizinde Kullanılan Temel Yaklaşımların Gözden Geçirilmesi

Fatigue damage occurs in welded steel joints under cyclic loads. These joints are particularly vulnerable to fatigue due to high stress concentrations. Today, with the developing numerical analysis software, fatigue life calculations are carried out with different methods based on the fatigue life and the stresses that will occur in the elements. These methods, which may differ from each other, examine the stress distributions occurring under different loading conditions and the initiation, development and collapse of the damage occurring in the element. Fatigue analysis methods are divided into two groups as local and global approaches. In global methods, the critical stress that will occur on the entire structure is considered, while local geometry and local parameters are examined in local methods. This study presents fatigue analysis methods of welded steel joints.

Effect of laser welding and laser wire filling on forming and properties of dissimilar steel welded joints

In order to study the effects of different welding methods and different butt gaps on the microstructure and properties of welded joints of steel with unequal thickness, the medium carbon steel of 2 mm 50CrV and low carbon steel of 6 mm SPHE were used as test materials, and the welding was carried out by single laser and laser wire filling welding. The results show that the laser wire filling welding can reduce the welding cracks, and with the increase of the butt gap, the melt height gradually decreases, and the weld morphology transitions from Y shape to H shape. With the increase of the butt gap, the weld defects form. The hardness of weld center decreases with the increase of butt gap. The average hardness of weld formed by laser welding alone is the highest, and the highest hardness of welded joint is located in the heat affected zone of 50CrV medium carbon steel. The tensile strength of welded joints first increases and then decreases with the increase of butt gaps. When the butt gap is 0.6 mm, the surface morphology is good and the tensile strength is the highest. The fracture position of the welding test is on the side of the 2 mm 50CrV medium carbon steel.

Effect of Ultrasonic Treatment on Microstructure and Properties of 2000 MPa Ultra-High-Strength Steel-Welded Joints

The microstructure and mechanical properties of ultra-high-strength steel weld joints were examined for the effect of ultrasonic treatment. ER120S-G welding wire is necessary for welding 4 mm thick ultra-high-strength steel. After that, the weld toe region underwent different parameters of the ultrasonic stress relief process. As a means of surface treatment for weld seams, noticeable grain refinement and the formation of a fine-grained layer were observed in the weld toe region after ultrasonic treatment. The blind hole method was used to measure residual stresses in the weld seam, which indicated a transition from tensile stress to compressive stress in the treated portion of the joint. Different ultrasonic treatment processes resulted in a significant increase in hardness values near the weld toe region during hardness testing. The hardness of the weld joint that was treated with ultrasound increased initially but then stabilized after increasing the frequency. The ultrasound-treated joints showed a significant improvement in both tensile strength and fracture elongation, as demonstrated in the tensile tests.

Effect of the Filler Metal and Shielding Gas on the Fatigue Life in HSLA Steels Welded Using the GMAW Process

The composition of the filler electrodes, as well as the shielding gases, has a strong impact on the static and dynamic properties of welded joints in HSLA steels. The content of Cr, Ni, and Mo, along with the shielding gases, helps maintain the hardness values in the HAZ of HSLA steels welded using the GMAW process, resulting in a positive impact on the fatigue life of the joints. Maintaining fatigue properties in the regions of the heat-affected zone is crucial. The increase in the size of the HAZ, coupled with microstructural changes, leads to a reduction in the hardness values in this region, contributing to a decrease in the fatigue life of welded joints. In this study, the effects of using different filler electrodes and shielding gases on the fatigue properties of welded joints in LNE 600 steel with a thickness of 4.75 mm, welded using the GMAW process, were evaluated. It was possible to observe a reduction in the hardness values in the HAZ region and a similar static resistance behavior for all evaluated conditions, except for the ER70S-6 electrode with 5% O2 gas, where the fatigue life showed better results with the application of the ER120S-G electrode.

Fatigue performance assessment of thick TIG-Dressing cruciform welded joints made by Q355D structural steel

TIG-Dressing treatment is often used for steel welded joints in construction machinery manufacturing as an effective and reliable method for post-weld fatigue strength improvement. This paper investigates the fatigue performance of thick Q355D cruciform joints in heavy load-carrying steel structures under different TIG-Dressing treatments. Two TIG-Dressing treatments for the full-penetration welded joints were used for fatigue tests considering filling metal during this post-welded processing. Experimental tests studied the fatigue strength of TIG-Dressing cruciform welded joints of Q355D structural steel. The geometric parameters and relevant statistical analyses were performed by actual 3D optical measurement. Moreover, the stress concentration factors are calculated according to the actual geometrics of the welded joint. On the other hand, the effective notch stress and hot spot stress methods were employed to evaluate the fatigue data of Load-Carrying Welded joints (LCWJs) under different notch radius. The collected fatigue data from the literature was compared with the tested data by the above methods. The results show that the fatigue strength of LCWJs under TIG-Dressing processing without filler metal is higher than those under the same TIG-Dressing treatment with filler metal. The effective notch stress method with a fictitious notch radius r = rtrue + 1 mm (rtrue is the actual notch radius at weld toe) could obtain smaller scatter bands for the tested fatigue data.

Microstructure and mechanical properties of AISI 410S ferritic stainless steel narrow gap weld using flux strip constraining arc welding

The achievement of high comprehensive mechanical properties in welded joints of ferritic stainless steels has attracted considerable attention in the manufacturing industry. Here, a low heat input flux strip constrained arc welding (FSCAW) was performed on a hot-rolled AISI 410S sheet. Defect free joints with a small HAZ width were obtained by one side welding both sides formation. The microstructure of HAZ consists of fine ferrite grains and a small amount of M23C6-decorated martensite due to short high-temperature residence time and rapid cooling rate, resulting in high toughness and hardness. Influenced by the stirring effect of the constraining arc and the promotion of heterogeneous grain nucleation by Ti-rich MX particles originating from the transition of alloying elements in the flux strip, the fusion zone (FZ) exhibits a unique precipitates-strengthened martensite+austensite uniform microstructure with weak martensitic texture. This translates into a simultaneous increase in impact toughness and hardness of FSCAW FZ compared to the MAG joint with a non-uniform mixed microstructure, strong martensitic texture, and large grain size. This work establishes the potential for using FSCAW welding to join ferrite stainless steels.

Structure and properties of welded joints of 13KhGMRB steel in pulsed-arc welding

Structure and properties of welded joints of 13KhGMRB steel in pulsed-arc welding

Study on the Influence of Repair Welding Process on the Microstructure and Mechanical Properties About 30CrMnSiNi2A High-Strength Steel Weld Joints

Study on the Influence of Repair Welding Process on the Microstructure and Mechanical Properties About 30CrMnSiNi2A High-Strength Steel Weld Joints

Microstructural aspects of fatigue strength of welded joints of medium carbon steels produced by rotary friction welding

The paper studies the resistance to fatigue failure of welded joints of steels 32Mn2-40CrNi2Mo, intended for the production of drill pipes for geological exploration. The connection of pipe billets for the purpose of manufacturing experimental samples was carried out by means of rotational friction welding at various process parameters. The assessment of resistance to fatigue loads was carried out on solid cylindrical samples with a welded joint under conditions of bending with rotation, which made it possible to identify the weakest zone in which the initiation and development of a fatigue crack occurred. The microstructure was studied using optical and electron scanning microscopy using the electron backscatter diffraction (EBSD) method. In the course of research, it was found that the greatest resistance to fatigue loads is provided due to the intensive development of strain hardening processes in the thermomechanical affected zone of welded joints, which depend on the parameters of rotary friction welding.

Mechanism Study of Stress Corrosion Behavior under Tensile and Compressive Stresses for Welded Joint Used in Nuclear Turbine Rotor.

Stress corrosion damage containing pitting and cracking was investigated for NiCrMoV steel-welded joint used in nuclear turbine rotor in 3.5% NaCl solution. The U-bend specimen containing tensile face and compressive face was adopted which was conducive to study the effects of stress on pitting and stress corrosion cracking. On tensile surface of U-bend specimen, pit grew in open environment and was converted into crack covered with passivated film. Interestingly, corrosion pit was also found on compressive surface, which might attribute to this location creating enclosed environment causing Cl- to diffuse hardly. Then, pit grew under the occluded oxide crust composed of special crystalline corrosion products. When pit approached to critical size, crack initiated from it. The critical size of pit for crack initiation from pit was 35 μm on tensile surface and 95 μm on compressive surface. The sensitivity of crack initiation in tensile surface was higher than that in compressive surface. Then, cracking on compressive surface was controlled by slip dissolution mechanism, that is, dislocation outcrop generated through plastic deformation during manufacturing and absorbed Cl- in enclosed environment to accelerate metal dissolution and film rupture. Thereupon, the stress corrosion cracking on compressive surface was able to be maintained. The findings compared corrosion damage modes caused by the two kinds of stress and emphasized the nonignorable role of compressive stress on stress corrosion damage.

Effect of PWHT on metallurgical and mechanical characterization of dissimilar welded joint of P91 and P92 steels

P91 and P92 steels are widely used in nuclear and thermal power plant’s high-temperature (650–700 °C) operating components. The welding procedure, base plate composition, filler material composition, and post-weld heat treatment (PWHT) significantly affect the metallurgical characterization of weldments at room temperature. This work focuses on joining P91 and P92 steel by the TIG welding with filler ER90S-B9. The study analyzes the materialization of coarse-grained HAZ (CGHAZ), inter-critical HAZ (ICHAZ), and fine grained HAZ (FGHAZ) under welded and PWHT. PWHT was conducted at 840 °C for 2, 4 and 6h. An optical microscopic (OM) scanning electron microscope (SEM) was employed to characterize the welded and PWHT samples. It was perceived that the tensile strength of PWHT increased as the heat treatment times increased from 2 to 6 h, while the hardness value decreased accordingly. The maximum tensile strength (594.71 MPa) was observed in PWHT_6 h, while the minimum tensile strength (537.52 MPa) was perceived in the as-welded sample. The PWHT_6h reveals the minimum hardness values (271.12 HV) at the fusion zone among all the conditions. The WFZ consisted of an untampered lath martensitic grain structure, demonstrating an average hardness value of 314.15 HV in the PWHT_2h condition. The hardness value in CGHAZ samples for as-welded, PWHT_2h, PWHT_4h, and PWHT_6h was observed at 456.85, 436.81, 368.63, and 327.41 HV, respectively.

Achieving superplastic TWIP steel welded joint via vacuum electron beam welding

A crack-free high-Mn TWIP steel welding joint with comparable strength and superplastic was obtained via vacuum electron beam welding (VEBW) where the microstructural evolution, mechanical behaviors and strengthening mechanism of welding joint were investigated. The results indicated that the welding joint with a typical nail-shaped welding cross-section was divided into three zones including the base metal (BM), heat-affected zone (HAZ) and fusion zone (FZ). Massive fine AlN-type precipitates with the hexagonal crystal structure were observed in welding join. The orientation relationship between the γ-austenite matrix and AlN precipitates was determined as [001]γ//[2110]AlN. In FZ, small-sized cellular grains or columnar grains with consistent growth directions were combined into large-sized columnar grains with obvious <001> preferential orientation. Compared with the base mantal, the yield strength, ultimate strength and elongation of the VEBWed specimen were slightly reduced by 6.03%, 4.7% and 13.23%, respectively. However, the impact toughness was obviously decreased from the 87.90 J–68.97 J after the VEBW process, which was mainly attributed to the brittle AlN precipitates, inhomogeneous microstructure and back stress induced by the plastic mismatch between gradient grains. The strength contributions of different regions to overall strength including of BM, HAZ and FZ in welding joint were calculated. Here, the dislocation strengthening and precipitation strengthening were the dominant strengthening mechanisms of FZ, which was attributed to the high level of density and massive fine AlN precipitates induced by micro-elements segregations during the VEBW process.