TIG Welding Of Steel Research Articles

Analyzing weld bead geometry and microstructure in ultrasonic-assisted activated flux TIG welding of ST37 steel

Analyzing weld bead geometry and microstructure in ultrasonic-assisted activated flux TIG welding of ST37 steel

Investigations of Microstructure and Mechanical Properties of Post-Weld Heat-Treated DP780 Steel TIG Welds

This study investigates the microstructure and mechanical properties of DP780 steel that has been tungsten inert gas welded and post weld heat treated. Microscopy studies revealed that the weldment’s microstructure varied from martensite in the fusion zone to a mixture of martensite and ferrite in the heat affected zone (HAZ). This heterogeneity in the microstructure resulted in the formation of hardened and softened zones in the cross section of the weldment. The DP780 as-welded joint exhibited lower strength and ductility [yield strength (YS): 492 ± 5 MPa, ultimate tensile strength (UTS): 668 ± 8 MPa, and percent elongation (%El): 8 ± 1] compared to the base metal (BM) (YS: 538 ± 2 MPa, UTS: 794 ± 5 MPa, and %El: 27 ± 2) due to strain localization in the subcritical HAZ. The weldments subjected to post weld heat treatment (PWHT) at 500°C exhibited lower strength and higher ductility (YS: 471 ± 3 MPa, UTS: 624 ± 5 MPa, and %El: 13 ± 1) than the weldments subjected to PWHT at other conditions: 300°C (YS: 501 ± 7MPa, UTS: 658 ± 6 MPa, and %El: 9 ± 1) and 400°C (YS: 492 ± 3 MPa, UTS: 649 ± 5 MPa, and %El: 11 ± 1). The decrease in strength and ductility after PWHT can be attributed to the tempering of martensite present in the weldment. Erichsen cupping tests indicated a reduction in the formability of the as-welded joint due to the presence of a softened zone. While a significant increase in formability is observed in the weldments subjected to PWHT with an increase in temperature, the formability is still inferior to that of the BM due to the inhomogeneity in the microstructures across the weldment.

Narrow-gap TIG welding of thick steel 20

Narrow-gap TIG welding of thick steel 20

Identifying the influence of the ultrasonic-arc technique on the He+ irradiation damage resistance of CLAM steel TIG welds

Identifying the influence of the ultrasonic-arc technique on the He+ irradiation damage resistance of CLAM steel TIG welds

Study on arc and TIG welding of earthquake-resistant structural steels with a higher carbon equivalent

Study on arc and TIG welding of earthquake-resistant structural steels with a higher carbon equivalent

Influence of Groove on Metal Vapour Behavior and Arc Characteristics in TIG Welding of High Manganese Stainless Steels

Influence of Groove on Metal Vapour Behavior and Arc Characteristics in TIG Welding of High Manganese Stainless Steels

Use of backing mediums increase penetration during TIG welding of P91 steel

Use of backing mediums increase penetration during TIG welding of P91 steel

Finite element and experiment analysis of welding residual stress in S355J2 steel considering the bainite transformation

This paper investigated the residual stress distribution and evolution in single-pass bead-on-plate TIG welding of S355J2 steel using the coupled thermo-metallurgical-mechanical model. The metallurgical calculation was based on parameterizing the continuous heating transformation and continuous cooling transformation diagrams. The simulated phase fraction in welding joints was validated against the dilatometric curves. The predicted results of welding residual stress revealed that the solid-state phase transformation incorporating undercooling austenite and transformation strain had significant consequences on the welding residual stress. The residual stress measurement was obtained by the XRD and relaxation methods. The good agreements between the simulated and experimental results indicated that the undercooling austenite and the bainitic transformation strain were crucial for predicting welding residual stress. The accurate thermo-metallurgical-mechanical model contributed to controlling the residual stress distribution reasonably by numerical method.

Activated flux TIG welding of austenitic stainless steels

The tungsten (W) inert gas (TIG) welding process that is applied with an active flux deposited on the workpiece surface just before welding is called activated flux TIG (A-TIG) welding. Layer deposition can be achieved by brushing or spraying over the surface, and welding is carried out after the surface dries out. This process has shown that it is possible to increase weld penetration and productivity up to three times higher or more compared with the TIG process in steels. In this review paper, A-TIG welding applications of steels were examined. The chemical composition and thickness of the flux and welding parameters (welding current, welding speed, arc length and shielding gas composition and its flow rate) affect the weld geometry. The activated flux welding mechanisms, effects of flux and welding parameters on weld geometry and microstructure and properties of A-TIG welds were explained.

Research on Automatic TIG Root Welding of Low Temperature Carbon Steel and Stainless Steel Pipeline for LNG Module Construction

We investigated the application of automatic TIG welding for LNG process pipeline in Yamal LNG module construction project. The study achieved efficient automatic TIG welding of low temperature carbon steel and stainless steel pipeline in root welding and hot welding. The properties of the weld meet the requirements of project technical specification and standard ASME B31.3. Welding efficiency increases 2 times compared with conventional manual TIG welding in root welding and hot welding. Therefore, the construction quality and progress of the project are improved.

A Three-Stage Mechanistic Model for Solidification Cracking During Welding of Steel

A three-stage mechanistic model for solidification cracking during TIG welding of steel is proposed from in situ synchrotron X-ray imaging of solidification cracking and subsequent analysis of fracture surfaces. Stage 1—Nucleation of inter-granular hot cracks: cracks nucleate inter-granularly in sub-surface where maximum volumetric strain is localized and volume fraction of liquid is less than 0.1; the crack nuclei occur at solute-enriched liquid pockets which remain trapped in increasingly impermeable semi-solid skeleton. Stage 2—Coalescence of cracks via inter-granular fracture: as the applied strain increases, cracks coalesce through inter-granular fracture; the coalescence path is preferential to the direction of the heat source and propagates through the grain boundaries to solidifying dendrites. Stage 3—Propagation through inter-dendritic hot tearing: inter-dendritic hot tearing occurs along the boundaries between solidifying columnar dendrites with higher liquid fraction. It is recommended that future solidification cracking criterion shall be based on the application of multiphase mechanics and fracture mechanics to the failure of semi-solid materials.

Numerical Simulation of Keyhole TIG Welding of Dissimilar Steels Based on Asymmetric Heat Source

Numerical Simulation of Keyhole TIG Welding of Dissimilar Steels Based on Asymmetric Heat Source

Optimization of hybrid laser – TIG welding of 316LN steel using response surface methodology (RSM)

In the present study, the hybrid laser – TIG welding parameters for welding of 316LN austenitic stainless steel have been investigated by combining a pulsed laser beam with a TIG welding heat source at the weld pool. Laser power, pulse frequency, pulse duration, TIG current were presumed as the welding process parameters whereas weld bead width, weld cross-sectional area and depth of penetration (DOP) were considered as the process responses. Central composite design was used to complete the design matrix and welding experiments were conducted based on the design matrix. Weld bead measurements were then carried out to generate the dataset. Multiple regression models correlating the process parameters with the responses have been developed. The accuracy of the models were found to be good. Then, the desirability approach optimization technique was employed for determining the optimum process parameters to obtain the desired weld bead profile. Validation experiments were then carried out from the determined optimum process parameters. There was good agreement between the predicted and measured values.

Some effects of the nitrogen introduction in argon shielding gas in TIG welding of stainless steels

In the case of austenitic stainless steels, nitrogen can be considered as alloying element. One reason is that the nitrogen, interstitially dissolved in the crystal lattice of iron contributes to improved tensile properties, primarily of the yield point. In addition, thanks to its strong austenite forming action contributes to increasing the stability of austenite, thereby enabling partial substitution of expensive and scarce nickel. Alloying of the weld metal of austenitic stainless steels with nitrogen can affect its properties. In welding processes with gas protection, weld metal can also be alloyed through the addition of nitrogen in the shielding gas. This paper discusses some of the effects of the addition of nitrogen in argon shielding gas at TIG welding of austenitic stainless steel X5 CrNi 18 10.

Residual stress characterization of steel TIG welds by neutron diffraction and by residual magnetic stray field mappings

The residual stress distribution of tungsten inert gas welded S235JRC+C plates was determined by means of neutron diffraction (ND). Large longitudinal residual stresses with maxima around 600 MPa were found. With these results as reference, the evaluation of residual stress with high spatial resolution GMR (giant magneto resistance) sensors was discussed. The experiments performed indicate a correlation between changes in residual stresses (ND) and the normal component of local residual magnetic stray fields (GMR). Spatial variations in the magnetic field strength perpendicular to the welds are in the order of the magnetic field of the earth.

Design of gas trailing shields for TIG-welding of stainless steels

In this paper, the suitability of different constructional concepts of gas trailing shields concerning the reduction of heat-tints is discussed. The evaluation of these concepts as well as the description of the main contamination mechanisms of gas trailing shields with atmospheric gases are performed for tungsten inert gas welding of stainless steel by a purposeful coupling of experimental as well as numerical methods. Furthermore, advantages and disadvantages of these design concepts are investigated regarding their constructional complexity, robustness against varying process parameters, and its feasible working distances. Finally, a modular concept is presented which allows the usage of the same constructional concept for a variety of different welding tasks.

슈퍼듀플렉스 스테인리스강의 TIG 용접에서 질소 침투 모델에 관한 연구

Superduplex stainless steels are important materials to the oil and gas industry, especially for off-shore production. TIG welding of super duplex stainless steels to obtain the optimal phase balance between austenite and ferrite is mainly achieved by controlling the cooling rate and the weld chemistry. The latter depends on the filler wire chosen and the shielding gas used. If TIG welding of superduplex stainless steels is performed with argon shielding gas only, then nitrogen gets lost from the weld pool, which can result in a ferrite-rich weld metal, with an inferior corrosion resistance than parent metal. In the present study, nitrogen permeation model from the shield gas which gets into the weld metal in DCEN-TIG welding has suggested. This plasma stream model shows characteristics of permeation of nitrogen ions into the molten metal due to the strong physical effect of plasma stream which formed by the arc pressure rather than the permeation of nitrogen ions caused by electric effect.

Effect of the Purging Gas on Properties of Ti Stabilized AISI 321 Stainless Steel TIG Welds

AbstractGas purging is necessary to provide a high quality of stainless steel pipe welding in order to prevent oxidation of the weld zone inside the pipe. AISI 321 stabilized austenitic stainless steel pipes commonly preferred in refinery applications have been welded by the TIG welding process both with and without the use of purging gas. As purging gases, Ar, N2, Ar +N2 and N2 + 10% H2 were used, respectively. The aim of this investigation is to detect the effect of purging gas on the weld joint properties such as microstructure, corrosion, strength and impact toughness. Macro sections and microstructures of the welds were investigated. Chemical composition analysis to obtain the nitrogen, oxygen and hydrogen content of the weld root was done by Leco analysis. Ferrite content of the beads including root and cap passes were measured by a ferritscope. Vickers hardness (HV10) values were obtained. Intergranular and pitting corrosion tests were applied to determine the corrosion resistance of all welds. Type of the purging gas affected pitting corrosion properties as well as the ferrite content and nitrogen, oxygen and hydrogen contents at the roots of the welds. Any hot cracking problems are not predicted as the weld still solidifies with ferrite in the primary phase as confirmed by microstructural and ferrite content analysis. Mechanical testing showed no significant change according to the purge gas. AISI 321 steel and 347 consumable compositions would permit use of nitrogen rich gases for root shielding without a risk of hot cracking.

Parametric Studies on Effect of Trailing Liquid Nitrogen Heat Sink on TIG Welding of Steels

Welding is an efficient material joining process. But the localised temperature rise up to the melting point in the vicinity of arc causes non uniform expansion and contraction resulting in residual stress and distortions. Post weld, Pre weld and in-process methods have been studied to reduce these unwanted effects of welding. A trailing heat sink is one such method. This consists of a cooling agent traversing at a constant distance behind the weld arc. Introduction of a cooling agent is reported to reduce the distortion. A liquid nitrogen jet is used as the cooling agent in the present study. A finite element model developed using Sysweld is used to study the effect of liquid nitrogen heat sink on weld distortions and residual stresses. The finite element model developed is used to make a parametric study on the effect of cooling jet radius, cooling strength and the distance between the jet and weld arc on out of plane distortions and stresses. Comparative study of the effect of cooling jet is made for mild steel (MS) and stainless steel (SS). It is observed that the out of plane distortions reduce with increasing cooling strength, jet radius. Reduction in distance between the jet and weld arc also causes a reduction in distortions.

Increasing the productivity of TIG welding of steels and aluminium alloys by adding ultrafine particles of activating fluxes

The results of investigations of the effect of ultrafine activating fluxes on the properties of the welding arc and the formation of welded joints in welding with direct in alternating current to increase the productivity of automatic argon-shielded arc welding of steels in aluminium alloys and improve the quality of welded joints are presented.