Weld Heat-affected Zone Research Articles

Corrosion Performance of Welded Joints for E40 Marine Steel

Marine steel requires excellent toughness and corrosion resistance in a low-temperature seawater environment. In this study, corrosion tests on E40 steel were performed, including electrochemical testing of the weld metal and heat-affected zone, dynamic corrosion testing in a simulated seawater environment, and the analysis and comparison of results obtained using different methods. The corrosion resistance of E40 was determined by measuring the saturation current density of the anodic dissolution of the steel in a corrosive medium by an electrochemical method. Under laboratory conditions, the corrosion resistance was investigated under simulated seawater. The results showed that regions with uneven microhardness corresponded to the inhomogeneity of the corrosion potential, with measured fluctuations of up to 40 mV. Nanoscale corrosive–aggressive non-metallic inclusions served as a substrate for the deposition of titanium and niobium carbonitrides, thereby weakening the corrosion resistance. The corrosion rate of the base metal was 1.16–1.64 mm/year, which was slightly higher than that of the heat-affected zone. The influence of deposition on the corrosion performance of welded joints under different deoxygenation processes was studied, and the deposition composition was controlled by a deoxygenation process to improve the corrosion resistance of the steel plate.

Impression creep behaviour of different zones of pulsed gas tungsten arc welded Ti-6Al-4V alloy

Ti-6Al-4V alloy has several industrial applications, because of their excellent combination of mechanical and physical properties. However, welding of Ti-6Al-4V alloy is very challenging due to its high reactivity with atmospheric gases at elevated temperatures (as low as 480 °C). In this work, defect-free bead on plate welding has been carried out on 3 mm-thick Ti-6Al-4V sheets with the help of an indigenously developed shielding set-up, using the pulsed gas tungsten arc welding (GTAW) process, and the impression creep responses of different zones of the weld have been investigated using the impression creep method. A detailed microstructural examination has been carried out, because the creep behaviour of each zone is dependent on the microstructure of that region. Base metal revealed a typical fine bi-modal microstructure with an average grain size of 4.2 µm, but there was significant grain coarsening in the heat affected zone (HAZ) and weld zone with an average prior β grain size of 37 µm and 105 µm respectively. Weld zone and HAZ also showed Widmanstätten morphology as fine laths of α inside the prior-β grains. Coarse prior-β grains and Widmanstätten morphology in HAZ and weld zone assisted in reducing grain boundary sliding and impeding dislocation glide, respectively, which led to an improvement in the creep resistance of these zones in comparison to base metal. In the testing range, dislocation creep appeared as the governing creep mechanism, where activation energies ranged from 255 to 312 kJ-mol−1 in different zones of the weldment.

Experimental and numerical study on the distribution of temperature field and residual stress in a multi-pass welded tube joint of Inconel 617 alloy

The purpose of this study is to compare the residual stress generation during hot wire gas tungsten arc welding (HW-GTAW) welding and conventional gas tungsten arc welding (GTAW) in a multi-pass pipe weld of a nickel-based superalloy. HW-GTAW yields better mechanical properties at low heat input than conventional GTAW, and decreases the accumulation of residual stress significantly. The distribution of residual stress developed in the through-thickness direction is determined experimentally using the Deep hole drilling method. As a result of the analysis, it was observed that the highest residual stress arises in Fusion Zone (FZ) and Heat Affected Zone (HAZ). In the case of conventional GTAW the hoop stress was observed to be tensile and distributed over 70% of the weld whereas only 20% of the weld is found to be under tensile hoop stress in the case of HW-GTAW along the weld center. The results show that shrinkage at the weld HAZ region affects the stresses produced at the cylinder's outer surface. The bending effect created during the welding process is primarily responsible for the distribution of residual stresses in the weld zone. A comprehensive numerical analysis has been carried out using ABAQUS software to predict the level of thermal and residual stresses in the weld zone, FZ, and HAZ in the case of both welding process. A 2D finite element models have been developed to simulate the welding process using the ABAQUS FE tool based on coupled thermal-mechanical analysis. A double ellipsoidal heat source model has been developed using a DFLUX subroutine file to simulate the welding process during the numerical analysis. The predicted residual stresses were validated with the experimentally obtained results.

FRACTURE SAFETY OF LIQUEFIED NATURAL GAS TANK IN CRYOGENIC CONDITIONS

High-manganese austenitic steel has been developed as a new cryogenic steel for application in liquified natural gas (LNG) storage and fuel tanks, with improved fracture toughness and safety at cryogenic temperatures. Generally, the fracture toughness decreases at lower temperatures; therefore, cryogenic steel requires a high fracture toughness to prevent unstable fractures. This study conducted unstable ductile fracture tests with 30-mm-thick high-manganese austenitic steel and evaluated its applicability to LNG storage and fuel tanks. The ductile fracture resistance in the weld joints was evaluated, including the weld metal and heat-affected zone. The unstable fracture resistance was evaluated for different LNG tank types. It was found that high-manganese austenitic steel has excellent unstable fracture characteristics and good material performance as a cryogenic steel; therefore, it can be applied in LNG storage and fuel tanks.

Microstructure and properties of underwater wet laser welded 0Cr25Ni6Mo3N duplex stainless steel joints

A self-designed welding flux was successfully applied to underwater wet welding of a 5 mm thick 0Cr25Ni6Mo3N duplex stainless steel in 6 mm simulated seawater. After welding, the microstructure of the weld centre, heat-affected zone, and base metal were observed using a metallographic microscope. Further, the microstructural evolution mechanism was derived, and the phase transition process of the metal in the fusion zone was analysed by thermodynamic calculations. After the experiment, the average tensile strength of the specimens was 811 MPa, which reached 95.3 % of the tensile strength of the base metal, and the average elongation was 35.5 %. The microstructure of the fracture showed obvious cleavage steps and a small number of tendons, which belonged to the mixed fracture type. The Vickers microhardness test results were as follows: the average values of the weld centre and the heat-affected zone are 297.7 HV and 278.0 HV. Electrochemical tests showed that the corrosion resistance of the weld were better and the passivation ability was weaker than that of the base metal.

Fatigue Crack Propagation Behavior and Life Prediction of Welded Joints of SMA490BW Steel for Bogies

In this paper, the precrack propagation behavior of an SMA490BW welded joint in the core zone and heat-affected zone was analyzed through experiments based on the FRANC 3D and ABAQUS cosimulation method, and life prediction of these cracks was also investigated. The results show that the experimental crack propagation path and crack propagation rate in the weld core zone and heat-affected zone agree well with the simulation results, with a small relative error. The life span of the prefabricated crack in the heat-affected zone was higher than that in the core zone. Furthermore, regarding the life prediction results for the two samples, the relative error obtained using FRANC 3D was about 5%, which was verified using the method of joint simulation of crack propagation behavior in the zone simulation and their life prediction with accurate feasibility.

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Weld Heat-Affected Zone of 2.25Cr-1Mo Steel

The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of 2.25Cr-1Mo steels was investigated. SA-387 Gr. 22 Cl. 2 steel was employed, and the specimens taken from the steel were thermally cycled using Gleeble to simulate the coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), and intercritical HAZ (ICHAZ). Before the PWHT, the simulated HAZs exhibited poor impact toughness as compared with the base metal. The base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730℃ for 8 h; their impact toughness improved significantly irrespective of the PWHT temperature. The microstructural changes owing to the PWHT were observed using scanning electron microscopy and correlated with the mechanical properties.

Microstructure and corrosion behavior of welded joint between 2507 super duplex stainless steel and E690 low alloy steel

Microstructure and corrosion behavior of welded joints between super duplex stainless steel 2507 and low alloy steel E690 were characterized herein. The joints are composed of base metal and heat affected zone (HAZ) of the two steels, weld metal, and dilution zone at the interface between weld metal and HAZ of E690 steel. Concentration gradients of Fe, Ni, Cr, and Mo exist between fusion boundary and Type-II boundary, and martensite band with a high hardness is formed. The changes of microstructure, element diffusion in different regions, and local acidification in E690 HAZ lead to heterogeneous corrosion attacks on the welded joints in artificial seawater. After long-term exposure, a corrosion groove is generated at the HAZ of E690 adjacent to the interface, where high stress corrosion cracking vulnerability is expected.

Investigation of mechanical and microstructural properties in joining dissimilar P355GH and stainless 316L steels by TIG welding process

In this study, the joining of high-temperature and pressure-resistant P355GH and austenitic stainless 316L steels by the Tungsten Inert Gas (TIG) welding method was investigated in terms of microstructure, mechanical properties, and weld efficiency. Comprehensive tests were carried out for the weld zone, heat-affected zones (HAZ), and base metals. In metallographic characterization research, optical microscope (OM), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX/EDS), X-ray diffraction (XRD), and EBSD analyses were performed. Average grain size and IPF (Inverse Pole Figure) map were determined from the EBSD analysis of P355GH steel, welded zone, heat-affected zones (HAZ), and 316L steel. Vickers microhardness, bending, Charpy V-Notch impact, and tensile tests were performed to determine the mechanical properties of the welded joint and the base materials. According to the EBSD results, the average grain size of the P355GH base metal was 5.13 ± 1 μm, the average grain size of the 316L base metal was 16.33 ± 5 μm, and the average grain size of the weld center was 10.09 ± 6 μm. As a result of XRD analysis, the delta ferrite phase was determined in the microstructure of the welding region. The highest Vickers microhardness value was determined as 268 ± 15 HV at the weld center. In the tensile test results, the highest tensile strength observed in the transverse weld joint was 593.92 ± 06 MPa and rupture occurred in the 316L region. Bending forces were measured as 34.331 ± 10 kN and 32.966 ± 11 kN for transverse and longitudinal welded samples, respectively. The TIG welding process showed superior properties such as toughness, high plastic deformability, and high weld efficiency of 101.89% in the joining of 316L and P355GH materials.

Effects of N2 content in shielding gas on microstructure and toughness of cold metal transfer and pulse hybrid welded joint for duplex stainless steel

The influences of N2 content in shielding gas on microstructure and impact toughness of different zones in cold metal transfer and pulse (CMT-P) hybrid welded joint of duplex stainless steel (DSS) were systematically studied. The results showed that the N2-supplemented in shielding gas significantly facilitated austenite formation (weld root: 39.9%→41.2%, weld filler: 40.5%→43.7%, and heat affected zone (HAZ): 36.4%→39.6%). However, when the N2 content in the shielding gas exceeded 4%, there was no significant change in austenite content because of reaching the solubility limit of N atoms. In addition, γ2 precipitated both in the weld root and HAZ but not in the weld filler, which cannot be inhibited by N2 addition in the shielding gas. Besides, a great number of Cr2N and dislocations in addition to γ2 formed in the HAZ, and the content of Cr2N and dislocation significantly increased with the increase of N2 content in the shielding gas. Furthermore, the HAZ exhibited the lowest toughness in comparison with other zones. In addition, with the increase of N2 content in the shielding gas from 0% to 6%, the toughness increased first and then decreased, and reached the maximum when 4% N2 added to the shielding gas as (weld root: 122.0 J/cm2, weld filler: 135.0 J/cm2, and HAZ: 91.8 J/cm2). According to detailed microstructure analysis and toughness level, Ar+4% N2 was recommended as the shielding gas to join DSS by using CMT-P welding technique.

Metoga GTAW Welding Joint Strength Study For Aisi 1045 Application Of Milling Tools

The welding process is a permanent connection process for metal materials using heat energy. The GTAW (Gas Tungsten Arc Welding) welding method is carried out on AISI 1045 steel material with a solid round shape, which has the characteristics and properties of the material slightly above low carbon steel. The welding process was carried out based on AWS A5.18 standard specifications, in this study. by varying the welding amperage between 70, 90, and 110 amperes as well as the ER70S-G series electrodes.To check the results of the welding with the amperage variation, perform tensile testing with standard ASTM A-370 testing, hardness testing using the Vickers method with standard ASTM E-92 testing, microstructure inspection, and grain size calculations as a control for the results of the hardness test. The focus of testing and inspection is carried out in three influential areas, namely, areas of weld metal, HAZ (heat-affected zone), and base metal.The results of this study show that for 70 A welding amperage, the tensile test results in all samples breaking in the weld metal area. While welding amperage 90A broke two samples in the weld metal area, welding amperage 110A broke one sample in the weld metal area. For the results of the hardness test at 110 A amperes, the hardness ratio in the weld metal area to the HAZ area shows that the difference in hardness is not too large compared to the two amperes used, so a welding amperage of 110 A can be recommended. While the results of the microstructure examination in the weld metal area were dominated by pearliet and martensite with a little bainite, the hardness results in the weld metal area were harder compared to the HAZ area and base metal. Likewise, the results of grain size calculations using the Heyn method for regions with higher hardness make the grain sizes appear denser and smaller.

Strain-based fracture analysis for internal surface cracks of X80 pipe girth welds

The girth weld is the weakest region of the entire pipeline. When the pipeline crosses areas with complex terrain or where natural disasters are frequent, the pipeline may be subjected to large displacement effects and large plastic deformations. In these scenarios, the traditional stress-based assessment methods will no longer be applicable. Therefore, it is of great importance to develop strain-based assessment methods for pipelines. This paper investigates the effects of crack size, strength mismatch, heat affected zone (HAZ) width and HAZ softening/hardening coefficient on the crack driving force (CDF) of weld center crack (WCC) and HAZ center crack (HAZCC) on the inner surface of X80 pipes using finite element method. The results show that the CDF is significantly affected by crack size, crack location, strength mismatch, HAZ softening coefficient but slightly affected by HAZ width when HAZ width is greater than 2 mm. The CDF of WCC is greater than that of HAZCC under large strain conditions with HAZ width of 2 mm. The distribution of the J-integral at the crack tip is then investigated and the results show that the maximum value of the J-integral does not necessarily occur at the deepest point of the crack tip. Finally, the factors influencing the failure assessment curve (FAC) of WCC are investigated and the lower bound strain-based failure assessment diagram (SB-FAD) considering strength mismatch and HAZ softening coefficient is developed with varying crack depths. This study can provide a reference for the safety assessment of crack-like defects on the inner surface of X80 pipeline girth welds.

Corrosion of Weld Heat-Affected Zones Submersed in Seawater with Indigenous Microorganisms

Corrosion of Weld Heat-Affected Zones Submersed in Seawater with Indigenous Microorganisms

Experimental research and numerical analysis of welding residual stress of butt welded joint of thick steel plate

The thickness of steel plates used in the member has gradually increased to meet the load-bearing capacity requirements of long-span steel bridges. As the primary connection method of thick steel plate, welding will result in considerable welding residual stress with complex distribution. Large welding residual stress will significantly impact the performance of steel bridges. In this paper, the distribution of residual stress in welded thick steel plate is systematically studied, a specimen with a thickness of 80 mm was designed and fabricated, and the welding residual stress was measured by X-ray diffraction. The finite element model was established and verified by test results. Subsequently, the finite element calculation of the welding residual stress of steel plates with thicknesses of 20, 40, 60, 80, and 100 mm was carried out, and the distribution of surface residual stress and the influence of plate thickness on residual surface stress were studied; then the spatial evolution mechanism of welding residual stress was studied, and the distribution of residual stress inside steel plate and the influence of plate thickness on the distribution of residual stress were revealed. The results show that the surface and internal residual stresses of 20–100 mm thick plates have good symmetry on the paths perpendicular to the weld seam, and asymmetry only occurs in the weld seam and heat-affected zone where the stress fluctuates. On the paths perpendicular to the weld seam, the stress in the X direction transitions from the “M” shape distribution on the surface to the “Π” shape distribution inside for 20–40 mm thick plates, and the residual stress near the weld seam gradually changes from compressive to tensile; The distribution of stress in the X direction in the 80–100 mm thick plate has experienced the transition from “M” shape to “Π” shape to “M” shape, and the stress near the weld seam has experienced the transition from compressive to tensile to compressive. The stress change in the X direction of the 60 mm thick plate is between the above two cases. On the path of internal stress along the thickness, the maximum stress in the X direction is 310–400 MPa for 20–40 mm thick plates, which appears at about 1/2 plate thickness. The maximum stress in the X direction for 60–100 mm thick plates is 400–480 MPa, which appears at 0.2–0.3 times the thickness of the plate from the upper surface. The results could serve as a reference for welding residual stress analysis and guide optimization design of steel bridges made of thick steel plate.

A comparative study on the mechanical behavior of S355J2 steel repair-welded joints

The mechanical behavior of repair-welded joints was particularly important for the service safety of steel structures. The microstructure and mechanical behavior of S355J2 steel base metal, welded and repair-welded joints were investigated in this paper. The low cycle fatigue tests on S355J2 steel base metal, welded, and repair-welded joints were conducted fully reversed with strain amplitudes varying from ±0.2% to ±1.1%. The results found that the microhardness of repair-welded joints decreased by about 20 HV with the growth in grain size of weld metal and heat-affected zone. Both elongations of welded and repair-welded joints were reduced by about 25.1% compared with the base metal. Considering the cyclic loading behavior, S355J2 steel base metal, welded, and repair-welded joints exhibited continuously softened, while the repair-welded joints exhibited a greater amount of softening than welded joints. Based on the Coffin-Manson equation, the decreased ratio of permissible total strain amplitude of repair-welded joints was significantly higher for medium and high cycle fatigue (> 104) compared to low cycle fatigue (< 104). The low cycle fatigue fracture surface shows that the defects in the repair-welded joints were the fatigue crack initiation position, but the S355J2 steel base metal and welded joints were initiated on the surface of the specimen.

Preliminary assessment of the possibility to use large-diameter pipes of Х52 steel for transportation of pure gaseous hydrogen under pressure

To assess resistance to hydrogen embrittlement caused by the presence of hydrogen in the transported product, and, accordingly, suitability of pipes for hydrogen transport, the base metal of large-diameter pipes of X52 strength class manufactured by JSC “ChelPipe” (part of the PJSC “TMK” group of companies) was studied. The work included the study of pure gaseous hydrogen effect under pressure up to 10 MPa on change in mechanical characteristics of the base metal of large-diameter pipes (LDP) during preliminary hydrogen charging for various time periods in a stationary autoclave under pressure, and during simultaneous loading with a slow strain rate (SSRT) under expected operating conditions. Results of the X52 LDP metal study show that there is no significant impact on the effect of gaseous hydrogen under pressure for up to 144 hours on mechanical characteristics of the base metal determined by static uniaxial tension (decrease in ductile characteristics does not exceed 9 %). During SSRT at a rate of not more than 1·10–6 s–1 in pure gaseous hydrogen environment under a pressure of 10 MPa, the change in strength and ductile characteristics does not exceed 13 % in comparison with reference tests in nitrogen environment under the same pressure. The results obtained allow us to consider that the base metal of low-alloy pipe steel with ferrite-perlite microstructure of X52 strength class is sufficiently resistant to hydrogen embrittlement. Final confirmation of the possibility to use LDP made from steel under study will be the results of further qualification tests, including the study of the weld metal and heat-affected zone properties.

Variation of liquation cracking susceptibility for over–aged 247LC superalloy repair weld heat–affected zone

In this study, the liquation cracking temperature range (LCTR) of over-aged 247LC superalloy repair welds was quantitatively evaluated using spot-Varestraint testing, especially for application in the repair weld heat-affected zone (HAZ). The metallurgical mechanism of the evaluated liquation cracking susceptibility and variation of the LCTRs of the over-aged 247LC superalloys was clarified by analyzing the microstructural characteristics at the liquation cracking surface, and using thermodynamic calculations. From the spot-Varestraint tests of the over-aged materials, the LCTR was quantitatively evaluated to be 410 and 620 K for the 500 and 1000 h over-aged specimens, respectively. These results demonstrate that the over-aged 247LC superalloys face significant and serious liquation cracking susceptibility in repair weld HAZ. Based on local element distributions at the liquation cracking surface, analyzed by transmission electron microscopy and the Thermo-Calc calculations, the underlying metallurgical mechanism of high LCTRs of overaged materials could be attributed to the precipitation of fine MC and M6C carbides during the over-aging treatment. The carbides promote local liquation at the interface between the gamma phase at temperatures lower than the equilibrium solidus (1530 K) of the 247LC. The estimated liquation initiation temperatures at the MC/γ and γ/M6C interfaces were 1125 and 1420 K, respectively.

Effect of grain orientation on microstructure and mechanical properties of laser welded joint of additive manufactured 300M steel

The mechanical properties of 300 M steel welded joint are closed related to the morphology and orientation of the grain. Laser welding was used to join the laser additive manufactured (LAM) 300 M steel. The effect of grain orientations (0°, 45°, 90°) on the microstructure and mechanical properties of the laser welded joint was studied. The results showed that with the increase of orientation, the columnar to equiaxed transition (CET) occurred in the center of the weld joint. Microstructures of the welding line, heat-affected zone (HAZ) and base metal presented obvious changes. The HAZ of the as-welded samples showed the highest micro-hardness, then the welding line, and the base metal was the lowest. After heat treatment, the micro-hardness of the whole joint became uniform. Grain orientation had great influence on tensile strength of the sample. With the increase of orientation, the tensile strength of the joints increased while the elongation was decreased. However, the strength of the heat-treated joints was significantly higher than that of the as-weld samples and presented little difference. Fractures mode of the as-welded and heat-treated joints showed the ductile fractures.

Effect of pearlitic and bainitic initial microstructure on cementite spheroidization in rail steels

To improve the performance of the rails and wheels for the railway industry, new microstructures need to be researched. Nevertheless, the soft region observed in the weld heat-affected zone (HAZ), caused by the spheroidization of cementite, leads to localized loss of hardness. A methodology for calculating the percentage of cementite spheroidization is not well defined in the literature. Accordingly, a new calculating method for determining the spheroidized cementite fraction was proposed through image analysis. This calculation method observes the cementite area/morphology, not the spheroidized cementite gross area. Two starting microstructures (pearlite and lower bainite) were compared in their spheroidization tendency by divorced eutectoid transformation (DET) during a simulated HAZ thermal cycle. The phase transformation kinetics through the heat treatments was also analyzed using high-resolution dilatometry tests. The results showed that the lower bainite has a higher tendency for cementite spheroidization than the pearlite due to its initial configuration of carbides. Furthermore, it was confirmed that the higher the cooling rates, the lower the spheroidization tendency.

Corrosion Resistance of Dissimilar GTA Welds for Offshore Applications

The pitting corrosion resistance of dissimilar pipeline steel API X70 and Super Duplex 2507 Stainless Steel gas tungsten arc (GTA) welds was studied. The GTA welds were fabricated using Super Duplex 2594 Filler Metal or austenitic 309L Filler Metal. The specimens extracted from the base metal, weld fusion zone, fusion boundary, and heat-affected zones (HAZs) were subjected to a potentiodynamic corrosion test in a 3.5% NaCl water solution. The weld made using the 309L Filler Metal was found to have a smaller pitting resistance equivalent number (PREN) difference between ferrite and austenite, making it more corrosion resistant than the weld fabricated using the 2594 Filler Metal. The HAZ on the X70 side was the most susceptible to pitting and galvanic corrosion for both filler metals.