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Microstructure, mechanical properties and corrosion behavior of austenitic stainless steel sheet joints welded by gas tungsten arc (GTA) and ultrasonic–wave–assisted gas tungsten pulsed arc (U–GTPA)

Xie Weifeng, Yang Chunli

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 2

177--190

EN

Here, ultrasonic–wave–assisted gas tungsten pulsed arc (U–GTPA) welding is proposed as a new alternative welding process to gas tungsten arc (GTA) welding. To better understand the advantages of this new process, in this paper, the microstructure, mechanical properties and corrosion behavior of GTA- and U–GTPA-welded joints of 316L stainless steel are systematically compared. These results show that the weld zone (WZ) depth-to-width ratio of the U–GTPA-welded joint increased, and the area of the equiaxed grain zone was larger than that of the GTA-welded joint. This results in finally increasing the strength and hardness for U–GTPA-welded joints, and the ultimate tensile strength and elongation of the U–GTPA-welded joints were 7.1% and 26.2% greater than those of the GTA-welded joint, respectively. For the U–GTPA-welded joint, under the action of the pulsed arc, the grain distribution with high-angle boundaries (HABs) was different from that of the GTA-welded joint. The minimum of the HAB fraction corresponded to the fracture position for both joints in tensile tests. It shows that a large number of HABs were beneficial in improving joint tensile properties. However, for electrochemical corrosion experiments of two WZs in 3.5% NaCl solution, despite this GTA WZ having a higher HAB fraction, the corrosion current density and corrosion potential of U–GTA WZ were lower and higher than those of the GTA WZ, respectively. The corrosion rate and corrosion sensitivity of U–GTPA WZ indicated good corrosion resistance.

2

Effect of post-weld heat treatment on thermal diffusivity in UNS S32304 duplex stainless steel welds

Betini E. G., Mucsi C. S., Luz T. S., Orlando M. T. D., Avettand-Fènoël M.-N., Rossi J. L.

Archives of Materials Science and Engineering

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2017

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Vol. 88, nr 2

49--58

EN

Purpose: The thermal diffusivity variation of UNS S32304 duplex stainless steel welds was studied after pulsed GTA welding autogenous process without filler addition. This property was measured in the transverse section of thin plates after welding process and post-heat treated at 750°C for 8 h followed by air-cooling. Design/methodology/approach: The present work reports measurements of thermal diffusivity using the laser-flash method. The thermal cycles of welding were acquired during welding by means of k-type thermocouples in regions near the weld joint. The used shielding gas was pure argon and 98% argon plus 2% of nitrogen. The temperature profiles were obtained using a digital data acquisition system. Findings: It was found an increase of thermal diffusivity after welding process and a decrease of these values after the heat treatment regarding the solidified weld pool zone, irrespective of the welding protection atmosphere. The microstructure was characterized and an increase of austenite phase in the solidified and heat-affected zones was observed for post-weld heat-treated samples. Research limitations/implications: It suggests more investigation and new measurements about the influence of the shielding gas variation on thermal diffusivity in the heat-affected zone. Practical implications: The nuclear industry, especially, requests alloys with high thermal stability in pipes for power generation systems and safe transportation equipment’s for radioactive material. Thus, the duplex stainless steel grades have improved this stability over standard grades and potentially increase the upper service temperature reliability of the equipment. Originality/value: After heat treatment, the welded plate with 98%Ar plus 2%N2 as shielding gas presented a thermal diffusivity closer to the as received sample. By means of 2%-nitrogen addition in shielding gas during GTAW welding of duplex stainless steel may facilitate austenite phase reformation, and then promotes stability on the thermal diffusivity of duplex stainless steels alloys.

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Wymagania spawalnicze dla instalacji rurociągowych w systemach dystrybucji gazów wysokiej czystości w przemyśle półprzewodnikowym

Meka K.

Przegląd Spawalnictwa

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2015

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R. 87, nr 5

72--77

PL

Hale fabryczne każdego producenta mikroprocesorów wyposażone są w setki kilometrów instalacji rurociągowych wykonanych ze stali stopowej do dystrybucji różnego rodzaju gazów technicznych stosowanych w produkcji elementów półprzewodnikowych. Technologia ich łączenia musi zachować szczelność i odporność na korozję całej instalacji. Ponadto system dystrybucji musi zagwarantować bardzo wysoką czystość gazów, co oznacza, że wysokiej i ultrawysokiej czystości gaz musi przejść przez rurociąg bez gromadzenia pyłów, wilgoci lub innych zanieczyszczeń. W przeszłości standardy wykonania rurociągów do transportu gazów w przemyśle półprzewodnikowym określały specyfikacje producentów. Tak zwane praktyczne lub standardowe procedury operacyjne (SOP – standard operating procedure) zostały opracowane przez wykonawców instalacji w celu dotrzymania rygorystycznych norm czystości narzuconych przez przemysł półprzewodnikowy. W latach 1993-94 międzynarodowe stowarzyszenie producentów i dostawców dla branży półprzewodnikowej SEMI wprowadziło dwie nowe normy, które dotyczą orbitalnego spawania metodą TIG instalacji do dystrybucji mediów w przemyśle mikro- i nano-elektroniki. Przepisami tymi są: SEMI F78 „Zasady spawania metodą TIG systemów dystrybucji mediów do zastosowań w przemyśle półprzewodnikowym” (Practice for Gas Tungsten Arc (GTA) Welding of Fluid Distribution Systems in Semiconductor Manufacturing Applications) – przedstawiają wytyczne dotyczące spawania podczas produkcji i montażu rurociągów oraz SEMI F81 „Specyfikacja dla badań wizualnych i oceny spoin wykonanych metodą TIG w systemach dystrybucji mediów do zastosowań w przemyśle półprzewodnikowym” (Specification for Visual Inspection and Acceptance of Gas Tungsten Arc (GTA) Welds in Fluid Distribution Systems in Semiconductor Manufacturing Applications) – opisują szczegóły badań wizualnych i kryteria oceny spoin. Artykuł opisuje procedury i wymagania tych dwóch norm.

EN

Workshops of every microchip manufacturer are equipped with hundreds kilometers of stainless steel tubing transporting gases used in production. The welding technology must maintain the integrity, corrosion resistance and leek free of the system. Additionally, high and ultra-high purity gases must be able to pass through the piping systems without accumulating particulates, moisture or other contaminates. In the past standards for semiconductor gas lines based on company specifications. Practices or standard operating procedures (SOPs) were issued by contractors to meet the high purity standards set by the industry. The society Semiconductor Equipment and Materials International (SEMI) in 1993-94 introduced two new standards that apply to orbital GTA welding in semiconductor fluid distribution systems. These standards are SEMI F78 “Practice for Gas Tungsten Arc (GTA) Welding of Fluid Distribution Systems in Semiconductor Manufacturing Applications” - a guideline for fabrication, and SEMI F81 “Specification for Visual Inspection and Acceptance of Gas Tungsten Arc (GTA) Welds in Fluid Distribution Systems in Semiconductor Manufacturing Applications” - weld acceptance criteria. The paper present procedures and requirements of these two standards.

4

Welding of metallic AlSi foams and AlSi–SiC composite foams

Nowacki J., Moraniec K.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 4

940--950

EN

In this paper, possibilities as well as limitations of aluminium foam welding are defined, and current state of the art methods are presented. In the face of difficulty of achieving joints with TIG welding, the authors’ own innovative methods of preparation of aluminium and composite foams top layer are proposed in order for the foams to be TIG and laser beam welded. Filler consumption was estimated for different variants of edge preparation. Joint structure was examined and tensile strength of the joints was tested. Joints whose strength exceeded the strength of parent material were obtained.

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Zrobotyzowane spawanie GTA złączy zakładkowych i spoin grzbietowych blach ze stali S235JRG2 i X5CrNi18-10

Luksa K.

Przegląd Spawalnictwa

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2008

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R. 80, nr 12

13-16

PL

Przedstawiono wyniki badań technologii spawania zrobotyzowanego GTA (TIG) złączy blach o grubości 1 mm bez dodatku spoiwa. Celem badań było uzyskanie możliwie dużej prędkości spawania złączy zakładkowych i spoin grzbietowych. Uzyskane prędkości spawania wynoszące 7-12 mm/s dla złączy stali S235JRG2 i 10-16 mm/s dla złączy stali X5CrNi18-8 są zbliżone do prędkości uzyskiwanych przy spawaniu plazmowym.

EN

The article offers a presentation of robotised GTA welding (TIG) of metal sheets 1 mm thick without filler metals. The research works focussed on achieving the maximum possible travel speed of overlapping and edge joint welding. The results demonstrated that welding speeds ranging from 7 to 12 mm/s for S235JRG2 steel welds and from 10 to 16 mm/s for X5CrNi18-8 steel welds were similar to those obtained by means of plasma-arc welding.

6

GTA remelting of surface spot defects

Klimpel A., Luksa K., Kik T.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 25, nr 2

73-76

EN

Purpose: A statistical model that explains the interaction between cross-section dimensions of a GTA remelted spot area and remelting parameters is presented. It will be utilized in the repair of an investment casting made of nickel-based superalloys. Design/methodology/approach: An experimental design of response surface was used to elaborate the model of GTA remelting. Results of experiments were verified experimentally. Findings: The dimensions and volume of a remelted area are a linear function of the GTA welding process parameters. It is possible to remelt small surface defects and keep a smooth surface. Research limitations/implications: Research results are limited to the tested range of parameters and base material properties. Changes in thermal conductivity can strongly influence the presented results. Crack sensitivity of material can restrict the range of parameters. Practical implications: Results of the research will help in the repair of surface spot defects of nickel-based superalloys. The proposed method of repair can help to minimize the number of rejected parts. Originality/value: A new approach to welding technology is presented. A statistical model of GTA remelting process could be a useful tool for the precise selection of process parameters.

7

Modelling of transport phenomena in gas tungsten arc welding

Farzadi A., Serajzadeh S., Kokabi A. H.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 7

417-420

EN

Purpose: Since numerical heat transfer and fluid flow models have provided significant insight into welding process and welded materials that could not been achieved otherwise, there has been an important interest in the quantitative representation of transport phenomena in the weld pool. On the other hand, the temperature and velocity distributions of the molten metal as well as the cooling rate after welding operation affect the weld geometry, the microstructure, and the mechanical properties of weld zone. This work demonstrates that the application of numerical transport phenomena can significantly add to the quantitative knowledge in welding and help the welding community in solving practical problems. Design/methodology/approach: The temperature and velocity fields are simulated using the solution of the equations of conversation of mass, energy and momentum in three-dimension and under steady-state heat transfer and fluid flow conditions. Findings: The weld pool geometry and various solidification parameters were calculated. The calculated weld pool geometries were in good agreement with the ones obtained using the experiments. The solidification parameters of G and G/R are determined. It is found that as the welding speed increases, the value of G/R at the weld pool centerline decreases. Research limitations/implications: Welding process used is this study is gas tungsten arc (GTA) welding and base metal is commercial pure aluminum. This model can be investigated to simulate other materials and welding processes. Also the results of this study such as the temperature field can be used in the simulation of microstructure, mechanical properties, etc of welding zone. Originality/value: In this research the solidification parameters of G, R and G/R can be used for prediction of the solidification morphology and the scale of the solidification structure.