Strength Of Weld Metal Research Articles

Experimental evaluation of multiple-component residual stress distribution in a dissimilar metal repair joint of ferritic/martensitic steel using the asymmetric-cut and the symmetric-cut contour method

A thick multi-pass butt-welded ferritic/martensitic steel (P91) joint is prepared and the local region of the weld is repaired with an ENiCrFe-3 nickel-based alloy using the manual metal arc welding method. The repair weld including part of the base metal is then subjected to ultrasonic impact treatment (UIT). A three-cut contour method, including two asymmetric cuts and one symmetric cut, is developed in the present study to obtain the two-dimensional residual stress distributions at different locations, and the stress release after multiple cuts is considered to get the original stress distribution before cuts. The measurement procedure is introduced in detail. The longitudinal stresses in the repair weld and the initial weld of the P91 steel joint, as well as the transverse stress at the weld center, are finally obtained. The effects of the dissimilar metal repair weld at the local region on the longitudinal and transverse welding residual stresses are investigated. In addition, the applicability of UIT to mitigate the surface stress in nickel-based alloy repair weld is analyzed. The results show that the transverse and longitudinal stresses in the nickel-based alloy repair weld are both tensile stresses, the maximum longitudinal stress is close to the yield strength of the B91 weld metal and occurs in the heat-affected zone of the repair weld located in the initial weld. Repair welding causes the internal transverse compressive stress region to be narrower than in the original weld. UIT can be used to introduce compressive stress to the surface layer of the nickel-based alloy repair weld.

Flux enhancement with titanium or vanadium oxides addition for superior submerged arc welding of HSLA steel plates

A high-strength low-alloy (HSLA) steel plate of 10 mm thickness underwent submerged arc welding with enhanced fluxes containing additional titanium oxide (TiO2) or vanadium oxide (V2O5). The addition of TiO2 led to the development of a finer acicular ferrite structure but coarsening the carbide and martensite/austenite (M/A) constituents, which marginally improved the hardness, tensile strength, and ductility of weld metal. Conversely, incorporating V2O5 facilitated a substantial vanadium absorption (0.7 wt. %) in the weld metal, giving rise to a distinctive acicular microstructure less reliant on ferrite nucleation at non-metallic inclusions than conventional acicular ferrite. The distinctive microstructure, unique to vanadium steels, combined lath bainite with irregularly shaped granular bainite. The resultant dual-mode bainitic structure, coupled with a more uniform distribution of refined microphase constituents, outperformed the conventional acicular ferrite, delivering more than 20% and 13% improvements in yield and tensile strengths respectively, as evidenced by transverse tensile tests on the weld metals.

Effect of laser beam wobbling and welding speed in X80 steel wire-fed laser root welds

A wobble laser was combined with a wire feed during laser root welding of X80 pipeline steel. The enlarged laser irradiation area and molten pool resulting from the laser beam wobbling provided a better gap-bridging ability, which is critical during laser welding of thick pipes. Applying laser beam wobbling enabled better control of filler metal dilution, which determined the weld metal microstructure and mechanical properties. In the present work, more bainite along with reduced acicular ferrite was formed in the wobble laser weld, due to the effect of dilution resulting from increased base material melting during wobbling beam, along with an inhomogeneous fusion zone microstructure. The instrumented indentation testing was utilized for the first time to distinguish the local yield strength variation of different regions of the fine weld zones, allowing one to verify if the weld metal strength meet the target value in industrial standards. As the productivity being improved when the welding speed increased from 1.0 to 1.5 m/min, the presence of more low temperature transformation products generated with a faster cooling led to a 26 HV higher hardness and a 70 MPa higher yield strength in the upper region of the fusion zone.

Effect of Travel Speed on the Properties of 5087 Aluminum Alloy Walls Produced by Wire and Arc Additive Manufacturing

An innovative Wire and Arc Additive Manufacturing combines the well-studied process of arc welding with direct energy deposition. Effect of travel speed 5.0 and 7.5 mm/s on the microstructure and mechanical properties of 5087 aluminum alloy was investigated. Five thousand eighty-three aluminum alloy was used as a substrate material and 5087 aluminum alloy was utilized as a filler material for the walls fabrication. The presence of pores reducing the strength of the overlay weld metal was detected on both overlay welds. The lower welding speed (5 mm/s) resulted in the smaller amount of porosity in comparison to higher welding speed (7.5 mm/s). Average pore area of wall No. 1 was 0.66% and wall No. 2 was 1.13%. It was found that higher welding speed affected the wall width and overlay weld bead geometry. Increase in welding speed led to a narrowing of wall width from 10.23 to 8.44 mm. The microstructure of weld metal matrix consisted of a α-Al substitution solid solution. The tensile strength of parallel to welding direction removed samples exceeded the tensile strength of perpendicular removed samples. It is a result of the cohesion of the layers in the overlay welding direction compared to the non-uniformity of the layers in the perpendicular direction. Furthermore, the tensile strength was higher in the case of travel speed of 5 mm/s in comparison to that of 7.5 mm/s.

Identifying the influence of transient thermal tensioning treatments on minimizing distortion and improving fatigue behavior of steel welded

Due to the cost efficiency of welding repairs, the use of transient thermal tensioning (TTT) has begun to be applied to minimize distortion and residual stresses, particularly on thin plates. However, it requires a long preheating time especially on large structures, so that the efficiency of welding process cannot be maximized. Application of TTT treatment using flame heater on TTT treatment which require no preheating time so that welding efficiency can be increased. The aims of this study are to investigate the TTT treatment in reducing distortion, investigate the effect of TTT treatment on tensile strength and hardness, investigate the microstructure and its effect on tensile strength and hardness, investigated the effect of TTT treatment on fatigue crack growth rate. In this research, TTT treatment was performed by flame heating on the both side of weld line integrated in welding process. Temperature in both side plates were controlled and measured using thermocouple. The tests on the weld joints were carried out including distortion measurement, microstructure examination, hardness measurement, tensile test and fatigue test. Results showed that the TTT (60) treatment is the most effective in decreasing the longitudinal distortion which placing the flame heating a 60 mm behind welding torch. It tends to increase the tensile strength of weld metal supported by its increasing hardness. The increase in the percentage of the acicular ferrite phase is linearly related to the tensile strength and hardness of the weld joint. The fatigue behavior could be improved by TTT treatment (60) which is associated with the effect of decreasing residual stress in the weld metal region. This treatment is the best parameter in an effort to increase the welding efficiency of the TTT method

Ultrasonic-assisted Pulsed TIG Welding (U-P-TIG) of Inconel 690 for Nuclear Power Plants

Inconel 690 has been extensively used in steam generator tubing materials for pressurized water reactors. In order to improve the weld quality of Inconel 690, ultrasonic-assisted pulsed tungsten inert gas (TIG) welding is studied. In this study, the macrostructure, microstructure, and mechanical properties of Inconel 690 weldments welded by TIG welding with and without ultrasonic assistance were investigated. The microstructures of the fusion zone (FZ) and heat-affected zones (HAZ) were examined by an optical microscope and the Electron Backscatter Diffraction (EBSD) technique, and weldment properties were compared through tensile and impact tests. Experimental results indicate that the base metal (BM) was composed of equiaxed crystalline austenite, and the austenite grains in the heat-affected zone were obviously grown; the fusion zone (FZ) was composed of columnar austenite. Besides, the ultrasonic assistance was effective in refining the structure and improving the strength and toughness of weld metal.

Mechanical properties of high strength steels and weld metals at arctic low temperatures

This paper attempts to acquire fundamental knowledge on the mechanical properties of high strength steels and the corresponding high strength weld metals at arctic low temperatures. Two types of high strength steels (Q890, Q960) and three types of high strength weld metals (made of ER100S-G, ER110S-G, ER120S-G feedstock wires) were tested at arctic low and ambient temperatures ranging from −75 °C to 25 °C. Tensile coupon specimens for steel materials were directly extracted from high strength steel plates, whilst robotic gas metal arc welding was employed to fabricate the tensile specimens of weld metals. The tensile coupon specimens were designed as per ASTM E8M and wire-cut into shapes. Twenty-three tensile coupon tests on high strength steels and eighteen tensile coupon tests on high strength weld metals were carried out. Coupon specimens were tested in liquid nitrogen cooling chamber to mimic the arctic low temperature environment. The stress–strain responses and key mechanical properties of high strength steels and weld metals at both ambient and arctic low temperatures are presented and discussed. Prediction equations for key mechanical properties, including the Young’s modulus, yield stress and ultimate tensile strength, of high strength steels and weld metals at arctic low temperatures were proposed.

Investigation of cold cracking resistance of HSLA 950A steel by taguchi optimization technique

Cold cracking is one of the major issues during welding High Strength Low Alloy (HSLA) 950A steel. The aim of the present research work is to optimize preheating temperature, the addition of oxide particles, and heat input using the Taguchi design of experiments for bead on plate, especially on the improved impact strength of weld metal. The experiments are carried out at three levels of mentioned parameters and Charpy impact strength is considered as a response. L27 orthogonal array is selected for experimentation in the present investigation using three parameters. An addition of vanadium oxide (V2O5) has acted as a nucleation site for acicular ferrite and enhanced the cold cracking resistance of investigated steel. The experimental results suggested that the impact strength of weldment is strongly influenced by pre-heating temperature (74.5%) and less influenced by oxide particle concentration (12.7%), and heat input (12.2%). Microstructure at HAZ revealed the presence of a small proportion of acicular ferrite of Widmanstatten morphology and upper bainite near weldment causes the reason for enhancement in cold cracking resistance. Fractographic examination revealed the presence of both ductile and brittle fracture modes, which attributed to higher and lower impact strength of weld joint respectively.

Effectiveness of Using Low‐Strength‐Grade Filler Wires for 800 MPa Grade Ultra‐High‐Strength Steels Laser Beam Welds

To match the strength of ultra‐high‐strength steel (850 MPa) during laser beam welding (LBW), various filler wires having under‐matching (520–640 MPa) and comparable‐matching (890 MPa) strength grades are used. All‐weld metals with no filler or fillers comprise low‐temperature transformation microstructures such as martensite and bainite, while the base metal (BM) comprises bainite, ferrite, and pearlite. All tensile fractures occur in the BM having the lowest hardness as compared to weld metal and heat‐affected zone. Therefore, the hardness and tensile properties of LBW exhibit insignificant variation regardless of the use of filler and their strength grades. This is because the cooling rate of LBW is fast, where a large dilution of the BM with high hardenability and a small deposition of the under‐matching filler occur at zero gap butt joints. To examine these LBW characteristics, the microstructural and hardness behaviors are successfully discussed through simulation of a continuous‐cooling transformation diagram using JMatPro software and cooling rate T9/3 using Rosenthal's two‐dimensional solution. To obtain the effect of lowering weld metal strength in LBW, it is necessary to increase more deposition of under‐matching filler by creating a gap between BMs, and/or to develop a filler of lower hardenability suitable for LBW.

Effect of strength mismatch on limit load of dissimilar metal welded joint for connecting pipe-nozzle of nuclear pressure vessel

The interface region cracks in dissimilar metal welded joint (DMWJ) for connecting pipe-nozzle of a reactor pressure vessel (RPV) to safe end are important concerned cracks in fracture assessment. In this work, based on a large amount of finite element analyses, the effect of strength mismatch on the limit loads of two interface cracks in an actual DMWJ has been investigated for wide ranges of strength mismatch factors and crack sizes. The results indicate that for shallower cracks, the limit load is dominated by fully yielding of the safe end pipe and are independent of strength mismatch and crack size. For deeper and longer cracks, the limit load is dominated by fully yielding of the ligament area materials. As the mismatch factor M increases from undermatch (M < 1) to overmatch (M > 1), the limit loads increase. To improve the load-bearing capacity of the DMWJ and prevent plastic collapse failure, a high degree of strength overmatch (increasing strength of buttering and weld metals) should be designed and adopted. The normalized limit load solutions as functions of mismatch factor and crack size have been obtained for the two interface cracks.

Testing, characterization and numerical prediction (uni-axial tension and bend test) of Double-side TIG welded SS321 plate for pressure vessel application

This study reports the welding of SS321 nuclear grade stainless steel employed for pressure vessel industries using the novel Double-side tungsten inert gas (DS-TIG) welding. The optimization technique (Taguchi-based Grey relational analysis (GRA)) used in this research will give firsthand knowledge to the industry concerning the process variables to produce quality weldments using the DS-TIG welding method. The optimized combination of input variables was noted to produce a butt joint with SS321 plate having 6 mm thickness: Arc length (Al) 3 mm, Arc current (I) 220 Amps, and Traverse speed (S) 120 mm/min. The Analysis of variance (ANOVA) table was created to estimate the significance of the input process variables in the weldments. The impact of process variables on the Depth of penetration: DoP and Bead width: BW in relation to the heat input was evaluated. The microstructural features and mechanical integrity of the DS-TIG weldment made with the optimized combination of input process variables were analyzed utilizing Optical microscopy, Electron back scattered diffraction (EBSD), Tensile, Hardness, Impact, and Bend tests. A Finite element (FE) model of uni-axial tension and bend test was developed to predict the tension strength (base and weld metal) and stress distribution during bend test of DS-TIG specimen. A good agreement between the experimental and predicted results was noticed (error less than 5%) in terms of stress vs. strain plot (uni-axial tension) and load vs. displacement plot (bend test).

Effect of the strength of steel sheets and wires on residual stress of thin steel sheet lap-fillet GMA weld joint

Weld residual stress of the lap fillet GMA welding joints which was performed using two strength grades of steel sheets and two strength grades of welding wires were measured. In addition, to consider the effects of steel sheet strength and weld metal strength on welding residual stress, thermal elastoplastic analysis using FEM was carried out for the experiments. As a result of the analysis using the temperature history of the heat-affected zone as a fitting parameter, the residual stress distributions near the toe were in agreement with the measurement in the FE analysis. Comparing the residual stress distributions in the direction perpendicular to the weld line on the weld metal surface near the toe, which is the occurring point of fatigue cracks in the FE analysis results, with the same steel sheet, the higher the weld metal strength the smaller the tensile residual stress. And comparing with the same wire, the higher the steel sheet strength the higher the tensile residual stress. The reason for the former is that when using high-strength wire, cooling transformation occurs at a lower temperature than using low-strength wire. As a result, it is considered that the tensile residual stress was effectively reduced by causing transformation expansion while the surrounding strength was high. The reason for the latter is considered to be that each stress value changes based on the yield stress of the steel sheet and weld metal because the plastic strain continues to occur in each direction until transformation occurs after welding. It was considered that the larger the ratio of the hardness of the weld metal to the base metal, the smaller the ratio of the residual stress of the weld metal near the toe to the yield stress.

Characterization of nanoscale precipitates and enhanced mechanical properties of high strength weld metals containing Cu additions after PWHT

In order to match rapidly development of high strength low alloy steels, the new metal cored wire contained copper was designed. The multi-pass weld metals were obtained by gas metal arc welding. Results show that microstructure of weld metals is bainite with M-A constituents, and there are nano-9RCu precipitates after PWHT. The weld metal as welded achieves 737 MPa of yield strength (YS) and 1097 MPa of ultimate tensile strength (UTS), with an elongation 8%. After PWHT, the YS and UTS are 725 MPa and 968 MPa, respectively, and elongation increases to 16%. The lower dislocations density and reduction of Cu element at solid solution state hence for the decrease of YS. As well, the nano-Cu precipitates and reduction of effective grain size make it increase. The combined effect of these factors makes YS decrease by only 12 MPa after PWHT. Besides, a good impact performance (46.6 J) can be obtained after PWHT, while it is only 27.7 J of weld metals as welded. The improved toughness of weld metals after PWHT is obtained by the contributions of finer effective grain size, soft bainite, and dispersed nano-9RCu precipitation. The nano-Cu precipitates can improve strength without damage to toughness of weld metal after PWHT.

Effect of Aluminum on Microstructure and Mechanical Properties of Weld Metal of Q960 Steel

High-strength low-alloy (HSLA) steel is used in important steel structural members because of its strength and plastic toughness. Q960 steel is HSLA steel obtained by adding an appropriate amount of alloy elements and quenching and tempering treatment on the basis of ordinary low-carbon steel. This kind of steel has strong hardenability due to the alloy elements added. Cold cracks, embrittlement and softening of the heat-affected zone easily occur after welding. In particular, the low-temperature impact toughness cannot meet the requirements and limits its use. In this paper, self-shielded welding is used to adjust the content of aluminum in flux-cored wire. The relationship between weld metal (WM) microstructure and strength and properties was studied by tensile test and impact test, and the influence mechanism of Al content on weld metal microstructure and properties was analyzed. The results show that when the content of Al is 0.21%, the impact energy at 0 °C~−60 °C is the best, the tensile strength can reach 1035 MPA and the number of pores is small. The size of inclusions in WM is mostly less than 1.0 μm Al2O3 spherical oxide. It can become the center of acicular ferrite (AF) and increase the nucleation probability. However, with the increase of Al content, large irregular AlN inclusions are produced, which reduces the tensile strength and impact energy of the welded joint.

Effects of weld geometry and HAZ property on low-cycle fatigue behavior of welded joint

A previous experimental study by the authors clearly indicated that, due to the delay of the crack initiation, the butt-welded joint with smoother weld toe profile and harder weld metal had a longer low-cycle fatigue life. In the present study, supplementary numerical studies considering weld geometries and inhomogeneous mechanical properties are executed. Monotonic tensile and strain-controlled low-cycle fatigue tests on the reheated round bars are firstly conducted to characterize the mechanical properties for different zones of the butt-welded joints. The test results are used to calibrate the material constitutive model, which is then embedded into three-dimensional finite element models to investigate the low-cycle fatigue behavior of the butt-welded joints. The numerical results suggest the necessity of considering the effects of inhomogeneous material properties when evaluating the low-cycle fatigue of welded joints. It is also confirmed that decreasing weld toe stress concentration and simultaneously increasing weld metal strength can maximally increase the low-cycle fatigue life of welded joints compared to the individual changes for either one. These findings are expected to provide some insights into the low-cycle fatigue life improvement of welded joints.

Design and development of aluminum alloy 6061-T6 pressure vessel liner for aerospace applications: A technical brief

This work mainly focuses on designing a novel aluminum alloy 6061-T6 pressure vessel liner intended for use in launch vehicles. Fabrication of custom-made welding fixtures for the assembly of liner parts, namely two hemispherical domes and end boss, is illustrated. The parts of the liner are joined using the cold metal transfer welding process, and the welding trials are performed to arrive at an optimized parametric range. The metallurgical characterization of weld joint reveals the existence of dendritic structures (equiaxed and columnar). Microhardness of base and weld metal was 70 and 65 HV, respectively. The tensile strength of base and weld metal was 290 and 197 MPa, respectively, yielding a joint efficiency of 68%. Finite-element analysis of a uniaxial tensile test was performed to predict the tensile strength and location of the fracture in base and weld metal. The experimental and predicted tensile test results were found to be in good agreement.

Strength mismatch effect on residual stress of 10CrNi3MoV steel considering the back-chipping process

The paper investigates the Welding Residual Stresses (WRS) of 10CrNi3MoV high strength steel multipass butt welded joints by experimental measurement and numerical calculation considering the effects of weld metal strength mismatch and back-chipping processing. Firstly, a thermo-metallurgical-mechanical simulation model was developed incorporating the Effect of Solid-State Phase Transformation (SSPT) to obtain multipass welding residual stress distributions after the back-chipping processing for evenmatched filler material. Phase transformation modeling of diffusionless transformation kinetics based on the Koistinen-Marburger formula was performed by a user subroutine implemented in ABAQUS. Additionally, strain transformation calculation due to volumetric and heating change during the SSPT was completed by the user-defined subroutine. Then, the effects of weldment mismatch and back-chipping processing on WRS for the multipass welds were analyzed. Comparing the calculated residual stress results (with and without consideration of SSPT) with experimental data shows that more accurate WRS predictions are obtained when the SSPT effect is incorporated in the simulation procedure. For evenmatched welded joints, the compressive WRS were distributed in the top and back weld layer due to the involvement of SSPT behavior. While the considerable tensile WRS in undermatched weldments was obtained without considering the SSPT, the magnitudes were lower than those in Heat Affected Zone (HAZ). The proposed finite element model can predict the WRS of high-strength steel multipass welded joints and provide a theoretical basis for conducting the structural integrity assessment.

Strength matching factor of pipeline girth weld designed by reliability method

Crack-like defects frequently form in pipes exposed to aggressive environments or during welding fabrication. Appropriate strength matching factors should be determined for welding process evaluation based on the reliability aspect. In this paper, the current research status of codes and standards related to the strength requirement of weld metals in the pipeline industry were reviewed. The results showed that almost all standards considered the lower limit of pipe tensile strength as a requirement for weld strength evaluation for specimens of cross-weld test breaking at the weld position. This was contradictory to the original intention of even-match or over-match of pipeline girth weld. The Monte Carlo Method was then employed to investigate the evolution of girth weld strength matching factor and pipeline failure probability under different high-low misalignments, fracture toughnesses, and standard deviations of pipe strength distribution. The data revealed significantly reduced probability of pipe failure as the weld metal strength matching factor increased. At the same strength matching factor, the failure probability of pipe decreased as fracture toughness of girth weld. The failure probability of pipe also declined as the misalignment and standard deviation of pipe strength distribution diminished. Based on the requirement of certain target reliability and strain demand, a semi-empirical prediction model of critical strength matching factor was proposed for engineering applications. The analysis of parameter sensitivity showed the relative importance of several parameters on the critical strength matching factor of girth weld, including high-low misalignment, standard deviation of pipe material strength distribution, and fracture toughness.

Evaluation of the High Cycle Fatigue Properties of Double-Side-Welded AISI 321 Plates Using GTAW Process for Pressure Vessels

Abstract Titanium-stabilized AISI 321 material (UNS S32100) is generally preferred in the pressure vessel industry as it is not sensitive to intergranular corrosion. In critical applications, the fatigue behavior of weld seams is among the most stringent requirements. The microstructural characteristics and fatigue performance double-side-welded AISI 321 plate having 6 mm thickness was evaluated in this work. AISI 321 was welded with double-side-gas tungsten arc welding (DS-GTAW) process. The fatigue behavior was examined with a loading ratio of R = 0.1 and frequency of 15 Hz for two different specimens: base metal (BM) and weld metal (WM). Monotonic tensile results shows the improved tensile properties of WM compared to BM samples. The fatigue strength of WM (150 MPa) was 25% higher than that of BM (120 MPa) specimen and is attributed to the increase in ferrite volume along with dendritic microstructure. The change in the fraction of low angle grain boundaries (LABs) and high angle grain boundaries (HABs) improved the tensile and fatigue properties. The stress amplitudes influenced the degree of striations in the BM and WM. Final fracture surfaces were characterized with dimples and microvoids, revealing the ductile mode of fatigue fracture. The fatigue rupture surfaces of BM and WM samples at different stress regimes are discussed.

Assessment of Provisions for Load Rating Gusset Plates in Steel Truss Bridges

Many states have load rated their truss bridge gusset plates following the guidelines published in 2009 by the Federal Highway Administration in response to the catastrophic failure of the I-35W Bridge. As the Manual of Bridge Evaluation released new load rating provisions after 2014, the urgency in adopting and applying these mandated provisions became a pending burden for state agencies requiring extensive work to update the ratings of gusset plates. Moreover, this paper argues that the current states’ load rating practices do not involve the rating for the welded gusset plate owing to the lack of established provisions. In addition, the gusset plate with no plans also poses particular challenges for the state agencies. To provide state agencies with better insights on the load rating approach of gusset plates, this paper presents a study that carefully reviewed the states’ current practices and load rating provisions. The results of the study indicate the necessity of adopting the new provisions, as the former load rating methodology exhibited inaccurate results in some cases. Additionally, this paper reviews extensive work done for welded connections and proposes a load rating guidance for welded gusset plates. To deliver better interpretations, a case study is provided for the welded gusset plates. This paper also reviews the evaluation method for deteriorations and staggered bolt patterns with relevant case studies. Lastly, the paper provides guidance on estimating the unknown bolt strength as well as weld metal strength for the gusset plate.