Weld Metal Region Research Articles

Creep damage modelling of P92 pipe weld at 675°C

Creep data from ferritic steel P92 parent material, weld metal, cross-weld and heat affected zone specimens tested at 675°C are used to establish material behaviour models necessary for describing the creep behaviour of a P92 pipe with a circumferential weld. The method for determining the material properties for the heat affected zone of a P92 weld, in a single state variable creep damage constitutive model, using the data from cross-weld and impression creep tests, is described. The material properties for the parent material and weld metal regions have been already been published.Creep continuum damage finite element analyses are subsequently performed for a P92 pipe containing a circumferential weld, subjected to internal pressure and end loading, in order to assess the high temperature integrity and failure behaviour of a typical power plant component, from which the lifetime and potential failure modes can be predicted.

Creep Crack Growth Behavior of a P91 Steel Weld

Modified 9Cr-1Mo steel (P91) weld joints operating at elevated temperatures are well known to be prone to premature failure due to cracking in the heat affected zone because of the gradients in microstructure, popularly referred to as Type IV cracking. A campaign was undertaken to study the creep crack growth behaviour of modified 9Cr-1Mo weld joints. Creep crack growth (CCG) tests were carried out on compact tension (CT) specimens machined from P91 weld joints prepared using multipass shielded manual metal arc welding procedure. Specimens with two notch locations have been employed, (i) within the weld metal, between the centreline and the fusion line and (ii) in the heat affected zone. Constant load CCG tests were carried out at different applied loads at 798 and 898 K. The C* - da/dt correlations (da/dt =A C*m) were established for both notch locations. At 898 K, a higher A (0.064) and lower m (0.533) for the case with notch placed in the HAZ, compared to those for the case of notch in the weld (0.0399 and 0.75 respectively) were observed indicating the higher creep crack growth in HAZ, confirming type IV cracking. The difference increases at lower C* levels which correspond to long term behaviour. Heavy creep damage was observed in the HAZ region even for the sample with notch in the weld, whereas the weld metal regions showed relatively less damage. As the crack grew, a change in its course to follow the HAZ region was observed.

Mechanical Properties of AISI 316L Austenitic Stainless Steels Welded by GTAW

In this study, AISI 316 L types of austenitic stainless steels are welded by GTAW (gas tungsten arc welding) using 430L and 2209 filler metals, respectively. Mechanical properties of 316L austenitic stainless steel weldments, such as tensile properties, hardness and impact properties are determined. GTA weld microstructures are presented by optical microscopy with 1000X magnifications of weld metal region. The values obtained for ultimate tensile strength, yield strength and percentage of elongation for the welded joints are compared to the data obtained. From this investigation, the result shows that the yield, tensile strength and impact energy values of 316L stainless steels welded by GTAW using 2209 filler metal is superior compared to 430L filler metal.

Evaluation of Electromagnetic Characteristics under Creep-fatigue Damage Process at Weld Region for Energy Structural Materials

Creep-fatigue damage for welded specimens of austenitic stainless steel SUS316FR and high-chromium steel Mod.9Cr-1Mo was investigated by magnetic characterization techniques such as vibrating sample magnetometry and magnetic force microscopy. In SUS316FR at weld metal region remanent magnetic flux density decreased as creep-fatigue strain increased and it resulted from the decrease of δ-ferrite at weld metal region. In Mod.9Cr-1Mo steel at weld metal region permeability increased and micro-vickers hardness decreased as creep-fatigue damage increased and it resulted from magnetic domain structures change during creep-fatigue. It was found that the creep-fatigue damage for these energy structural materials was related to magnetic characteristics change which caused by micro-magnetic structure.

Very High Cycle Fatigue Properties of Welded Joints under High Frequency Loading

Very high cycle fatigue (VHCF) properties of welded joints under ultrasonic fatigue loading have been investigated for titanium alloy (TI-6Al-4V) and bridge steel (Q345). Ultrasonic fatigue tests of base metal and welded joints were carried out in ambient air at room temperature at a stress ratio R=-1. It was observed that the fatigue strength of welded joints reduced by 50-60% as compared to the base metal. The S-N fatigue curves in the range of 107~109 cycles of base metal and welded joints for both materials exhibited the characteristic of continually decreasing type. The fatigue failure still occurred after 107 cycles of loading, and the fatigue limit in traditional does not exist. The fatigue facture mainly located in the weld metal region at low cycle fatigue range, but in the fusion area in HCF and VHCF. Analysis of fracture surfaces analyzed by SEM revealed that the fatigue cracks initiated from welding defects such as pores, cracks and inclusions.

Hydrogen effects in duplex stainless steel welded joints – electrochemical studies

In this work results on the influence of hydrogen on passivity and corrosion resistance of 2205 duplex stainless steel (DSS) welded joints are described. The results were discussed by taking into account three different areas on the welded joint: weld metal (WM), heat-affected zone (HAZ) and parent metal. The corrosion resistance was qualified with the polarization curves registered in a synthetic sea water. The conclusion is that, hydrogen may seriously deteriorate the passive film stability and corrosion resistance to pitting of 2205 DSS welded joints. The presence of hydrogen in passive films increases corrosion current density and decreases the potential of the film breakdown. It was also found that degree of susceptibility to hydrogen degradation was dependent on the hydrogen charging conditions. WM region has been revealed as the most sensitive to hydrogen action.

Analysis of metallurgical and mechanical properties of laser welded super austenitic stainless steel

PurposeLaser welding under high power, high degree of automation and high production rate is extremely advantageous in automotive application. Super austenitic stainless steel is the preferable material for high corrosion resistance requirements. These steels are relatively cheaper than austenitic stainless steel and it is expensive than nickel base super alloys for such applications. The main purpose of this paper is to present the investigations of the microstructure and mechanical properties of super austenitic stainless steel butt joints made by 3.5 kW cooled slab CO2 laser welding using different shielding gases such as argon, nitrogen and helium.Design/methodology/approachThe tensile and impact tests were performed and the fractured surfaces were analyzed by scanning electron microscope. The hardness across the joint zone was measured. The X‐ray diffraction technique was used to analyze the phase composition. The microstructure of the laser welds were analyzed through optical microscopy.FindingsThe tensile sample fractures indicate that the specimen fails in a ductile manner under the action of tensile loading. The impact fracture surfaces of the different shielding gas laser welded joints show mixed mode fractures, that is, ductile and cleavage fractures. The hardness values of the Helium shielded laser joints in the weld metal regions are much higher than the others.Research limitations/implicationsThere is no limitation, except for the availability of the high beam power laser welding machine.Practical implicationsThe only practical implication is the laser welding shop hazard during the experiment.Social implicationsSocial implication is limited. The only hazard during the laser welding is that it may affect human body tissues.Originality/valueThe research work described in the paper is original.

Fatigue Performance of Gas Tungsten Arc, Electron Beam, and Laser Beam Welded Ti-6Al-4V Alloy Joints

Titanium alloys have been successfully applied for aerospace, ship, and chemical industries because they possess many good characteristics such as high strength to weight ratio, superior corrosion resistance, and excellent high temperature resistance. Though these alloys show reasonable weldability characteristics, the joint properties are greatly influenced by the welding processes. The evaluation and prediction of fatigue life are very important for the welded joints to avoid catastrophic failure particularly in titanium alloys. This article compares the fatigue performance of Ti-6Al-4V alloy fabricated by gas tungsten arc welding, laser beam welding, and electron beam welding processes. The resultant fatigue properties of the welded joints are correlated with the tensile properties and microstructural characteristics. Of the three processes considered the joint welded by laser beam welding exhibits higher fatigue limit when compared with the other two processes due to the presence of fine lamellar microstructure in the weld metal region.

Effects of Thermal Aging on Ductile-to-Brittle Transition Temperature Behavior of Welded A516 Steel

Prolonged high temperature exposure of welded C-Mn steels is likely to cause microstructural changes leading to an inrease in the ductile-to-brittle transition temperature (DBTT) of the welded joint. Consequently, such degrading material properties should be quantified in view of establishing accurate component life prediction model. This study examined effects of isothermal aging on DBTT behavior of the heat affected zone (HAZ) in welded Type A516 Gr 70 steels. Microstructures of the as-received weld region revealed the presence of pearlite and ferrite in the base metal while upper and lower bainite are found in the HAZ and weld metal, respectively. Hardness measures for the weld metal region, HAZ and base steel are 172, 209 and 150, respectively. Aging at 420 oC, 500 hours lowers hardness value of the HAZ by 20 %. A series of Charpy impact tests on V-notched specimens are performed for as-received and thermally aged samples at 420 oC for 500, 800 and 1200 hours. Results showed that the absorbed impact energy displays a sigmoidal variation with test temperatures. DBTT ranges from -60 to 5 oC for HAZ while narrow range from -25 to 12 oC for weld metal region. Absorbed impact energy variations in samples aged for durations up to 800 hours display another saturation level over test temperatures between -30 to 10 oC. Fractographic analysis on HAZ fracture surface indicated brittle fracture at -60 oC while ductile failure dominated at 27.7 oC. A mix-mode fracture mechanism is displayed for test conducted at -38 oC.

Fatigue crack propagation in API 5L X-70 pipeline steel longitudinal welded joints under constant and variable amplitudes

Fatigue crack propagation (FCP) under constant and variable amplitude loading in base metal (BM), weld metal (WM) and heat affected zone (HAZ) of longitudinal welded joints of an API X-70 pipeline steel was investigated. Constant amplitude loading tests were performed at R = 0.1 and 0.5, whereas for variable amplitude testing single peak tensile overloads (OLs) alternating between 75 and 100% of maximum load were applied at 2.5 mm intervals in crack growth. Results of SE(B) specimens tested under constant and variable amplitude loading revealed that BM, WM and HAZ regions subjected to R = 0.5 and low ΔK-values presented the highest crack growth rates. At higher ΔK values FCP rates in all the studied regions were similar and the R effect on FCP rate was no more observed. Crack growth retardation due to OLs was observed at the three studied regions, showing a decrease on the FCP delay with a decreasing on ΔK.

An Investigation on Microstructure and Mechanical Properties of Nd:YAG Laser Beam Weld of Copper Beryllium Alloy

Nd:YAG pulsed laser beam welding is conducted on UNS-C17200 copper beryllium sheet. Welding is carried out in the as-annealed and as-aged conditions to investigate the effects of preweld condition on weld microstructure and mechanical properties. Two different heat treatments including direct age treating and solution annealing + subsequent age treating are considered after welding. The mechanical and microstructural characteristics of weld metal regions (WMs) and heat-affected zones (HAZ) of four different samples are considered using tensile tests, hardness measurements, optical microscopy, electron microscopy, and X-ray diffraction (XRD). Results indicate that the microstructural and mechanical properties of the HAZ without postweld treatment are adversely affected by grain boundary liquation observed if welding is carried out in the as-aged condition. Tensile strength and hardness of the WM are improved after a postweld artificial age treatment at 315 °C for 3 hours. However, hardness of the WM is lower than that of the base metal (BM) and HAZ, because the precipitation mechanism in the fusion zone is not as effective as that is in the HAZ and BM. The CuBe secondary phase precipitates during solidification. The precipitates/matrix interface is incoherent, which does not significantly raise the hardness of the weld metal. Incoherent interdendritic precipitates are dissolved in the weld structure after postweld solution annealing. Having performed postweld solution treatment and aging, full strength and hardness throughout the copper beryllium material were observed.

Oxidation behavior of base metal, weld metal and HAZ regions of SMAW weldment in ASTM SA210 GrA1 steel

Shielded metal arc welding (SMAW) was used to weld together ASTM SA210 GrA1 steel. The oxidation studies were conducted on different regions of shielded metal arc weldment i.e., base metal, weld metal and heat affected zone (HAZ) specimens after exposure to air at 900 °C under cyclic conditions. The thermo-gravimetric technique was used to establish kinetics of oxidation. X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive analysis (SEM/EDAX) techniques were used to analyze the oxidation products. Base metal showed more weight gain than that of weld metal and HAZ. The HAZ specimen showed the least weight gain due to the formation of densely inner oxide scale.

Estimation of Gurson material parameters in bimetallic weldments for the nuclear reactor heat transport piping system

Bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system itself is the critical part of a nuclear reactor. Any failure of this system can lead to very grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. This paper describes the experimental efforts towards estimation of Gurson material parameters of base metal and weld metal regions of a BMW so as to use the micromechanical modelling approach for addressing the structural integrity issues in BMWs.

Investigations on the influence of post weld heat treatment on fatigue crack growth behaviour of electron beam welded AA2219 alloy

This paper reports the influence of post weld heat treatment on fatigue crack growth behaviour of electron beam welded AA2219 aluminium alloy. An attempt has been made to enhance the fatigue crack growth resistance of the electron beam welded joints through post weld heat treatment methods such as solution treatment (ST), artificial aging (AA), solution treatment and artificial aging (STA). Electron beam welding machine with 100 kV capacity has been used to fabricate the square butt joints. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN has been used to evaluate the fatigue crack growth behaviour of the welded joints. Of the three post weld heat treated joints, the solution treated and aged (STA) joints are offering better resistance against the growing fatigue cracks. The superior mechanical properties, preferred microstructures in the weld metal region and favourable residual stress field of the weld region are found to be the reasons for superior fatigue performance of the STA joints compared to other joints.

Effect of post weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy

Aluminum alloy 2219 (Al-6.5%Cu) is a favourite age hardenable alloy for aerospace applications because of its excellent welding characteristics. Though AA2219 has got an edge over its 6000 and 7000 series counterparts in terms of weldability, it also suffers from poor joint strength when welded. In this investigation an attempt has been made to improve the welded joint strength through post weld aging treatment. This paper presents the effect of post-weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy. Square butt joints were fabricated using an electron beam welding (EBW) machine of 100 kV capacity. The joints were given post-weld artificial aging treatment. Tensile tests were carried out using 100 kN, electro-mechanical controlled universal testing machine. It is found that the post-weld aging treatment is beneficial for improving weld metal hardness and tensile properties. This is mainly due to the uniform distribution of CuAl2 precipitates in the weld metal region in post-weld aged joints compared to as welded joints as evident from weld metal microstructure.

Influence of Welding Speed on Microstructure and Oxidation Behaviour of Laser Welded Austenitic Stainless Steels

Microstructure and high temperature oxidation behaviour of laser weldments of 316L and 316LN steels have been found to influence by the variation in welding speed. Ferrite content and ferrite morphology change for both type 316L and 316LN laser weld with welding speed. Laser weldments consisting mainly of weld metal and base metal region of two austenitic stainless steels (ASS) were oxidized in dry air at 973 K for 240 h. Steel weldment was found to have a higher oxidation rate when joined with lower welding speed of 11.66 mm/s as compared to 25 mm/s speed. On the other hand, 316LN steel weldments have indicated much superior oxidation resistance property under similar condition. Oxidation behaviour of two ASS weldments has been correlated with microstructure and oxide scales formed over the different regions have been characterized by scanning electron microscopy (SEM/EDXA).

Parametric Analysis of Stresses in Welded Branched Pipes Under Creep Conditions

The effect of weld properties on the steady-state creep rupture stresses, failure lives, and failure positions within multi-material finite element models of three typical branched steam pipe configurations is investigated using service-aged CrMoV creep properties. A general formulation, multi-material interpolation technique for steady-state creep is shown to be applicable to the parametric study of a three-material welded branched pipe with respect to the steady-state creep constants. An approximate interpolation procedure for power-law creep is implemented to reduce the number of analyses needed to span the range of material parameters. The method is used to predict creep stresses at several critical regions within the heat-affected zones, parent material, and weld metal regions of the branched pipe for three typical CrMoV weldment material sets. The advantages of the method are related to the small number of analyses required and the simple and compact way of presenting results for weld assessment and design. The results can be used to improve life-assessment procedures and to provide guidance to component designers.

Effect of prestraining and strain-aging on toughness of MnMoNi steel weld metal

Specimens of both as-deposited and reheated submerged arc weld MnMoNi weld metal have been subjected to plastic deformation and static strain-aging treatments. These treatments were carried out in an attempt to simulate some aspects of the thermomechanical conditions occurring in pressurised water reactor components such as the ferritic pressure vessel. Ductile to brittle transition curves were investigated using Charpy impact tests. The influence of such treatments on the tensile properties was also studied. The strain-aging treatment is found to have a more pronounced effect on the impact toughness of the as-deposited (AD) weld-metal region than of the reheated microstructure (RH).

Fracture toughness test for flux cored wire welded joint

Test techniques using unloading compliance single specimens to determine crack opening displacement (COD) resistance curves for flux cored arc welded joints were investigated in detail. Computer based methods for data acquisition and processing were incorporated in the test procedure. The causes of the shorter calculated crack length in comparison with the length measured according to unloading compliance single specimen techniques were studied, and the counter measures used to correct the crack length were analysed. The COD resistance curves for YJ657 basic flux cored wire (FCW) weld metal and joint line regions were then obtained using these techniques. The correlation coefficient using the least squares method to fit the curves was greater than 0.99. The results showed that the present test system and computer based data acquisition and processing techniques offered advantages such as flexibility of operation, stability of performance, and high accuracy when they were used to measure the COD resistance curves for FCW welded joints. The test results also indicated that the characteristic value of fracture toughness (extrapolated COD at zero crack length) for the YJ657 basic FCW weld metal and joint lines at 253 K was greater than 0.1 mm, indicating high toughness. This was because the weld metal microstructure consisted of a large proportion of acicular ferrite plates which were in different orientations and therefore able to deflect propagating cleavage cracks.

Solidification and microstructure modelling of welds in aluminium alloys 5754 and 6111

A solidification and microstructure modelling approach has been developed to predict weld metal and heat affected zone (HAZ) characteristics. The freezing range and phase evolution in the weld metal region were predicted using thermodynamic and diffusion controlled growth calculations. The calculated freezing range was correlated with the weld solidification cracking tendency. A simplified analytical model was suggested to describe thermal cycles that are experienced by the HAZ. This analytical model was coupled with a published microstructure model for age hardenable alloys to predict the hardness variations across the HAZ. The above integrated approach was evaluated using experimental welds made on non­age hardenable 5754 (Al–Mg) and age hardenable 6111 (Al–Mg–Si) alloys using gas tungsten arc, electron beam, and gas metal arc welding processes.