scholarly journals Shielding Gas Influence On AA5086 Welded Joints: Residual Stresses Analysis, Microstructural Characterisation and Mechanical Properties

2021 ◽  
Author(s):  
Maria Cindra Fonseca ◽  
Marcos Caetano Melado ◽  
Marcel Souza ◽  
Cássio Barbosa
Keyword(s):  
Residual Stresses ◽  
Weld Metal ◽  
Base Metal ◽  
Welded Joints ◽  
Gas Mixture ◽  
Shielding Gas ◽  
Pure Argon ◽  
Gas Tungsten Arc ◽  
Microstructural Characterisation ◽  
Mechanical And Microstructural Properties

Abstract Samples of AA5086 aluminium alloy were welded by gas tungsten arc welding (GTAW) with alternating current using three different shielding gases. The samples were welded with pure argon (Ar), a mixture of argon and helium (Ar + He) and a new mixture composed of argon, nitrous oxide and oxygen (Ar + N2O + O2). The effect of the shielding gas on the residual stresses and on the mechanical and microstructural properties of the welded joints was evaluated and compared with the base metal. The new gas mixture produced compressive residual stresses in the longitudinal and transverse directions in the weld metal. Tensile test of welded joints indicated similar values for yield strength and ultimate tensile strength; however, these values were lower compared to the base metal. The new gas mixture provided a welded joint with hardness values in the weld metal and heat affected zone close to the base metal values and with greater magnitude compared to samples welded using pure argon and mixture of argon and helium. Microstructural characterisation performed by optical and scanning electron microscopy showed that the new mixture produced welded joints with lower porosity.

Apply the Acoustoelastic Method to Determine Residual Stresses in Welded Joints

NDT World ◽  
2020 ◽  
pp. 10-17
Author(s):  
Arkady Kamyshev ◽  
Aleksandr Danilov ◽  
Lev Pasmanik ◽  
Aleksandr Getman ◽  
Dmitry Kuzmin ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Weld Metal ◽  
Base Metal ◽  
Welded Joints ◽  
Nuclear Power ◽  
Power Plants ◽  
Stress Measurement ◽  
Metal Structure ◽  
Mechanical Tests ◽  
Residual Welding

The problem of maximum stresses estimation in the weld metal, where the direct measurements are not possible due to the influence of the metal structure on the measurement error, was solved. The influence of features of welding joints manufacturing technology on the structure of the weld metal was also determined. We use several reference welded joints of pipelines at nuclear power plants in our studies. Instrumental estimation of acoustoelasticity parameters in the weld metal in welded joints and in adjacent areas of the base metal was used together with computational modeling of the residual welding stresses distributions. Results obtained demonstrate that the error of stress measurement in the metal in the joint, which is related to the structure of the weld metal, is comparable to the material yield strength. Due to that a direct measurement of the maximum values of welding stresses is not possible. Comparison of results of acoustoelasticity parameters measurements with results of the metal macrostructure studies and mechanical tests allowed us to determine the relationship between peculiarities of structure of the weld metal sections at vertical joints with their tendency to brittle destruction. We propose and justify the NDT method of residual welding stresses in the weld metal. It is based on the principle of residual stresses balancing and employs the results of stress measurements in the base metal by acoustoelasticity. Applicability of non-destructive testing of acoustoelasticity parameters to identify the areas of welded joints with a higher tendency to brittle fracture is also justified.

Creep Strength Evaluation of a New and a Used Grade 91 Welded Joints by Using a Miniature Specimen

2018 ◽  
Author(s):  
Takashi Ogata
Keyword(s):  
Weld Metal ◽  
Strain Rate ◽  
Creep Strain ◽  
Base Metal ◽  
Welded Joints ◽  
Welded Joint ◽  
Creep Damage ◽  
Creep Strain Rate ◽  
Standard Size ◽  
Grade 91

Grade 91 is widely used for steam pipes and tubes in high temperature boilers of ultra-super critical power plants in Japan. It was reported that creep damage may initiate at the fine grain region within the heat affected zone (HAZ) in welded joints prior to the base metal, so called “Type IV” damage, which causes steam leakage in existing power plants. Therefore, development of creep damage assessment methods is not only an important but also an urgent subject to maintain operation reliability. In order to evaluate creep damage of welded joints based on finite element analyses, creep deformation properties of a base metal, a weld metal and a HAZ have to be obtained from creep tests. However, it is difficult to cut a standard size creep specimen from the HAZ region. Only a miniature size specimen is available from the narrow HAZ region. Therefore, development of creep testing and evaluation technique for miniature size specimens is highly expected. In this study, a miniature tensile type solid bar specimen with 1mm diameter was machined from a base metal, a weld metal and a HAZ of a new and a used Grade 91 welded joints, and creep tests of these miniature specimens were conducted by using a special developed creep testing machine. It was found that creep deformation property is almost identical between the base metal and weld metal, and creep strain rate of the HAZ is much faster than that of these metals in the new welded joint. Relationships between stress and creep strain rates of the base metal and the HAZ in the used welded joint are within scatter bands of those in the new material. On the other hand, creep strain rate of the weld metal in the used welded joint became much faster than that in the new one. Then both the standard size and the miniature size cross weld specimens were machined from the new and the used welded joints and were tested under the same temperature and stress conditions. Rupture time of the miniature cross weld specimen is much shorter than that of the standard size cross weld specimen. The finite element creep analysis of the specimens indicates that higher triaxiality stress yields within the HAZ of the standard size specimen than that of the miniature specimen causing faster creep strain rate in the HAZ of the miniature cross weld specimen.

Application of FIB/SEM/EBSD for Evaluation of Residual Strains and Their Relationship to Weld Metal Hydrogen Assisted Cold Cracking

2012 ◽  
Author(s):  
W. L. Costin ◽  
I. H. Brown ◽  
L. Green ◽  
R. Ghomashchi
Keyword(s):  
Residual Stresses ◽  
Weld Metal ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Ion Beam ◽  
Base Material ◽  
Welding Process ◽  
Cold Cracking ◽  
Predictive Methods ◽  
Residual Strains

Hydrogen assisted cold cracking (HACC) is a welding defect which may occur in the heat affected zone (HAZ) of the base metal or in the weld metal (WM). Initially the appearance of HACC was associated more closely with the HAZ of the base metal. However, recent developments in advanced steel processing have considerably improved the base material quality, thereby causing a shift of HACC to the WM itself. This represents a very serious problem for industry, because most of the predictive methods are intended for prevention of HACC in the HAZ of the base metal, not in the weld metal [1]. HACC in welded components is affected by three main interrelated factors, i.e. a microstructure, hydrogen concentration and stress level [2–4]. In general, residual stresses resulting from the welding process are unavoidable and their presence significantly influences the susceptibility of weld microstructures to cracking, particularly if hydrogen is introduced during welding [5]. Therefore various weldability tests have been developed over the years which are specifically designed to promote HACC by generating critical stress levels in the weld metal region due to special restraint conditions [4, 6–8]. These tests were used to develop predictive methods based on empirical criteria in order to estimate the cracking susceptibility of both the heat-affected zone and weld metal [4]. However, although the relationship between residual stress, hydrogen and HACC has received considerable attention, the interaction of residual stresses and microstructure in particular at microscopic scales is still not well understood [5, 9–21]. Therefore the current paper focuses on the development and assessment of techniques using Focused Ion Beam (FIB), Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction for the determination of local residual strains at (sub) micron scales in E8010 weld metal, used for the root pass of X70 pipeline girth welds, and their relationship to the WM microstructure. The measurement of these strains could be used to evaluate the pre-existing stress magnitudes at certain microstructural features [22].

Effect of Filler Alloy on Microstructure, Mechanical and Corrosion Behaviour of Dissimilar Weldment between Aisi 201 Stainless Steel and Low Carbon Steel Sheets Produced by a Gas Tungsten Arc Welding

2012 ◽  
Vol 581-582 ◽  
pp. 808-816 ◽  
Author(s):  
Chuaiphan Wichan ◽  
Srijaroenpramong Loeshpahn
Keyword(s):  
Stainless Steel ◽  
Carbon Steel ◽  
Weld Metal ◽  
Base Metal ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Delta Ferrite ◽  
Steel Sheets ◽  
Gas Tungsten Arc ◽  
Weld Metals

The joining of austenitic stainless steel (AISI 201) to low carbon steel sheets (CS) was attempted by gas tungsten arc welding (GTAW) with four types of consumables. The studied consumables were ER308L, ER309L, ER316L stainless steel wires, and AWS A5.18 carbon steel wire. The welding parameters – i.e. the current of 90 A and the welding speed of 62 mm.min-1 – were fixed in all welding operations. The microstructure of weld metal produced by stainless steel consumables consisted of delta ferrite in austenite matrix. The delta ferrite in the form of continuous dendrite was observed in weld metals produced by 308L and 309L fillers. The dendrite of delta ferrite was relatively discontinuous in weld metal produced by 316L filler. The microstructure of weld metal produced by carbon steel filler consisted of equiaxed ferrite and pearlite, similar to that of carbon steel. The corrosion behavior of weld metal was investigated by potentiodynamic method. Specimens were tested in 0.35-wt% NaCl solution saturated by laboratory air at 27°C. It was found that the corrosion potential of weld metal produced by carbon steel filler was considerably lower than those of AISI 201 base metal and weld metals welded using stainless steel consumables. Weld metals produced by stainless steel fillers –308L,309L and316L– exhibited the similar corrosion potentials as that of 201 base metal. The pitting potentials of weld metals produced by 309L, 316L fillers were higher than those of 201 base metal and weld metal produced by 308L filler respectively. It was discussed that the increase of Cr content in weld metals by using 309L filler contained with 24.791 wt% of Cr, or the addition of Cr and Mo in weld metals by using 316L filler contained with 21.347 wt% of Cr and 2 wt% of Mo, promoted the pitting corrosion resistance of weld metal to be comparable with that of Fe-17Cr-3Ni (201) base metal. An emission spectroscopy was applied to quantify the amount of elements in weld metals. By considering the contents of Cr and Mo, the pitting resistance equivalent number (PREN) of each weld metal was calculated. The discussion of the corrosion resistance of weld metals related to PREN and microstructure was made in the paper.

scholarly journals Shielded Metal Arc and Thermite Welding Effect to Residual Stress, Hardness and Crack of R54-Rail Weld Joint

2020 ◽  
Vol 55 (4) ◽  
Author(s):  
Yurianto ◽  
Gunawan Dwi Haryadi ◽  
Sri Nugroho ◽  
Sulardjaka ◽  
Susilo Adi Widayanto
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Arc Welding ◽  
Welding Process ◽  
Shielded Metal Arc Welding ◽  
Metal Arc Welding ◽  
Crack Susceptibility

The heating and cooling at the end of the welding process can cause residual stresses that are permanent and remain in the welded joint. This study aims to evaluate the magnitude and direction of residual stresses on the base metal and heat-affected zone of rail joints welded by the manual shielded metal arc and thermite welding. This research supports the feasibility of welding for rail. The material used in this study is the R-54 rail type, and the procedure used two rail samples of one meter long each, welded using manual shielded metal arc welding and thermite welding. The base metal and heat-affected zone of the welded joints were scanned with neutron ray diffraction. The scan produces a spectrum pattern and reveals the direction of the residual stress along with it. We found the strain value contained in both types of welded joints by looking at the microstrain values, which we obtained using the Bragg equation. The results show that the magnitude and direction of the residual stress produced by manual shielded metal arc welding and thermite welding are not the same. Thermite welding produces lower residual stress (lower crack susceptibility) than manual shielded metal arc welding. The melt's freezing starts from the edge to the center of the weld to create random residual stresses. The residual stress results of both the manual shielded metal arc welding and thermite welding are still below the yield strength of the base metal.

Microstructural Characterization and Corrosion Behavior of Activated Flux Gas Tungsten Arc-Welded and Multipass Gas Tungsten Arc-Welded Stainless Steel Weld Joints in Nitric Acid

CORROSION ◽  
10.5006/0515 ◽  
2012 ◽  
Vol 68 (8) ◽  
pp. 762-773 ◽  
Author(s):  
A. Ravi Shankar ◽  
S. Niyanth ◽  
M. Vasudevan ◽  
U. Kamachi Mudali
Keyword(s):  
Stainless Steel ◽  
Weld Metal ◽  
Base Metal ◽  
Corrosion Behavior ◽  
Delta Ferrite ◽  
Thick Sample ◽  
Weld Joints ◽  
Gas Tungsten Arc ◽  
Gtaw Process ◽  
Gas Tungsten

AISI Type 304L (UNS S30403) austenitic stainless steels are widely used in spent nuclear fuel reprocessing plants, and welding is an indispensable tool used for joining these materials. In the present study, manual gas tungsten arc-welded (M-GTAW) and activated gas tungsten arc-welded (A-GTAW) weldments of Type 304L stainless steel were prepared to examine the microstructural and corrosion behavior of the weldments. A total of 6 passes were required to complete the 6 mm thick sample welding, and 16 passes were required for 12 mm thick sample welding using the M-GTAW process, compared to single-pass A-GTAW welding. Characterization of weld joints was done by radiography, optical microscopy, microhardness tester, a feritscope, and scanning electron microscopy (SEM). The optical microstructure of the fusion zone of weld joints showed delta ferrite in various morphologies. The presence of delta ferrite stringers were observed in the weld joints, extending from the weld metal to the base metal. The corrosion rate results showed that the M-GTAW sample showed only a marginal increase in the corrosion resistance when compared to those welded by the single-pass A-GTAW process. SEM examination revealed the morphology of attack in the base metal was predominantly intergranular while in the weld metal it was interdendritic. The SEM micrograph also showed preferential attack of the delta ferrite stringers.

Heating Characteristics of Gas Tungsten Arc Welding of Copper Thick Plates with Shielding Gas of Argon, Helium or Nitrogen

2007 ◽  
Vol 353-358 ◽  
pp. 2096-2099 ◽  
Author(s):  
Jiu Chun Yan ◽  
Yi Nan Li ◽  
Wei Wei Zhao ◽  
Shi Qin Yang
Keyword(s):  
Welded Joints ◽  
Arc Welding ◽  
Gas Tungsten Arc Welding ◽  
Rise Velocity ◽  
Shielding Gas ◽  
Welding Temperature ◽  
Thick Plates ◽  
Gas Tungsten Arc ◽  
Gas Tungsten ◽  
Weld Pools

The welding temperature patterns of gas tungsten arc welding for copper thick plates during Ar, He or N2 shielded arc welding were simulated, and the size of weld pools and heat-affected zones have been compared. It was predicted that the heat-affected zone in the welded joints during Ar arc welding is the widest and that during N2 arc welding is the narrowest, while the size of weld pools using Ar (preheating at 400°C), He and N2 (without preheating) shielding arc welding is very similar. Among the three kinds of gases shielded arc welding, the temperature gradient of welded joints during Ar arc welding is the least and that during N2 arc welding is the greatest. The temperature rise velocity at the arc center during N2 arc welding is the highest, and those at the zone close to the weld pool of welded joints during He arc and N2 arc welding are a few higher than that during Ar arc welding.

scholarly journals Influence of Friction Pressure at a Given Burn-off Length on the Mechanical and Microstructural Properties of Welded Joints from Medium-Carbon Alloyed Steels in Rotaty Friction Welding

2018 ◽  
Vol 7 (4.36) ◽  
pp. 978
Author(s):  
Elena Priymak ◽  
Nadezhda Firsova ◽  
Elena Bashirova ◽  
Svetlana Sergienko ◽  
Elena Kuzmina ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Welded Joints ◽  
Friction Welding ◽  
Thermal Deformation ◽  
Tensile Tests ◽  
Welding Parameters ◽  
Microstructural Properties ◽  
Medium Carbon ◽  
Friction Pressure ◽  
Mechanical And Microstructural Properties

This study investigates the influence of friction pressure at a given  burn-off length on the microhardness, tensile properties and microstructure of the welded joints from steel 32-2-Mn and 40-Cr-Ni. Phase transformations occurring in the materials to be welded as a result of thermal deformation effects are analyzed. The change in the length of the thermomechanical affected zone (TMAZ) depending on the friction pressure is shown. The results of the distribution of microhardness in the weld, clearly illustrating the formation of hardened and weakened areas. The results of tensile tests of welded joints are given. Analyzed the place of fracture at various welding parameters. The necessity of studying the distribution of internal residual stresses to explain the mechanism of fracture of welded joints is shown.  

Sign in / Sign up

Export Citation Format

Share Document