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Correlation between Tensile Deformation Behavior and Microstructural Morphology of Nuclear Grade Austenitic Stainless Steel Welded Joints using Infrared Thermography Technique

Rajasekaran R., Lakshminarayanan A. K., Menaka M.

Welding Technology Review

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2020

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R. 92, nr 1

7--15

EN

Tensile deformation behavior of nuclear grade Austenitic Stainless Steel (SS) and its welded joints fabricated by Gas Tungsten Arc Welding (GTAW) and Activated Flux Gas Tungsten Arc Welding (AGTAW) processes were studied and correlated with relevant microstructural morphologies using Infrared Thermography (IRT) technique. The microstructure of base metal showed a complete austenite phase. GTAW Fusion Zone (FZ) exhibited both primary ferrite and primary austenite mode of solidification. Meantime, AGTAW FZ exhibited only primary austenite mode of solidification. A strain rate of 4.4x10-4 s-1 was used during the tensile test of the base metal and welded joints. The failure locations of the base metal, GTAW and AGTAW samples were noticed at the center of the gauge portion, the base metal side away from Fusion Line (FL) and Heat Affected Zone (HAZ) respectively. The temperature variations of the base metal and weld zones were recorded in the form of thermograms using the IR camera at the different stages of the tensile deformation. During deformation study, peak temperature of 39.2 °C, 38.8 °C and 34 °C were observed at the base metal, GTAW and AGTAW samples respectively. The lesser peak temperature of the AGTAW sample compared to the base metal and GTAW samples indicated that the AGTAW sample undergone lesser deformation. Moreover, tensile deformation behaviours of the base metal and welded joints were correlated with their microstructural morphologies using corresponding temperature curves.

PL

W pracy zbadano zachowanie deformacji podczas rozciągania austenitycznej stali nierdzewnej i jej połączeń spawanych wykonanych metodą GTAW (Gas Tungsten Arc Welding) oraz AGTAW (Activated Flux Gas Tungsten Arc Welding), a następnie skorelowano je z odpowiednimi morfologiami mikrostrukturalnymi za pomocą termografii w podczerwieni (ang. lnfrared Thermography). Mikrostruktura materiału bazowego wykazała całkowitą fazę austenitu. Spoina GTAW wykazywała zarówno ferryt, jak i austenit, podczas gdy spoina AGTAW wykazywała jedynie austenit. Podczas próby rozciągania materiału bazowego i złączy spawanych zastosowano prędkość odkształcania o wartości 4,4x10-4 s-1. Do zerwania poszczególnych próbek doszło odpowiednio na środku próbki materiału bazowego, w linii wtopienia złącza spawanego GTAW i w strefie wpływu ciepła (SWC) złącza spawanego AGTAW. Zmiany temperatury w materiale rodzimym i poszczególnych obszarach złączy spawanych rejestrowano w formie termogramów za pomocą kamery na podczerwień, przy różnych etapach deformacji podczas rozciągania. Podczas badań odkształceń zaobserwowano maksymalne wartości temperatury: 39,2 °C, 38,8 °C i 34 °C odpowiednio w próbkach z materiału bazowego, spawanych GTAW i spawanych AGTAW. Niższa maksymalna temperatura próbki spawanej metodą AGTAW w porównaniu z pozostałymi próbkami wskazała, że uległa ona mniejszemu odkształceniu. Ponadto zachowania deformacji przy rozciąganiu materiału rodzimego i złączy spawanych zostały skorelowane z obrazami ich mikrostruktur przy użyciu odpowiednich krzywych temperatur.

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A combined full-field imaging and metallography approach to assess the local properties of gas tungsten arc welded copper–stainless steel joints

Saranarayanan R., Lakshminarayanan A. K., Venkatraman B.

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 1

251--267

EN

The local material properties of gas tungsten arc welded (GTAW) C21000 grade copper alloy (Cu) to AISI 304 grade stainless steel (SS) joints using (ErNiCu-7) filler material are studied using a range of material characterization techniques. Electron Back Scattered Diffraction (EBSD) studies across the weld confirmed the relationships existing between the solidification modes (dendritic, planar) and their corresponding grain morphology in a high resolution. The SEM-Backscattered Electron Mode (BSE) integrated with Energy Dispersive Spectroscopy (EDS) analysis evidenced the local heterogeneous compositions across the dissimilar weld. The global and local mechanical performance of the weld joints are assessed using a conventional uniaxial tensile tests and full-field 2D-digital image correlation (DIC) respectively. The local material behaviour of the weld joint is in-line with the compositional and microstructural gradients. The weld joint has achieved the ultimate tensile strength (UTS) of 258 ± 14 MPa, which is very close to the strength of the Cu base metal (BM) and all the joints were fractured in the Cu-HAZ. Microhardness distributions measured using a spatially positioned indents found that the weld fusion zone (129.28 ± 19.22 HV) has higher hardness in compared to the Cu-BM (80.51 ± 2.58 HV).

3

Enhancing the properties of friction stir welded stainless steel joints via multi-criteria optimization

Lakshminarayanan A. K.

Archives of Civil and Mechanical Engineering

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2016

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Vol. 16, no. 4

605--617

EN

An attempt is made to establish empirical relationships to predict the properties of friction stir welded stainless steel joints. The process parameters namely, rotational speed, welding speed and shoulder diameter and the properties such as tensile strength, notch tensile strength, impact toughness and degree of sensitization are considered. The investigated properties are correlated with the macrostructure and microstructural characteristics of different zones of FSW joints to understand the influence of process parameters. Multi-criteria optimization is used to obtain optimum welding conditions that can yield enhanced properties of FSW joints. The optimized results indicated that, the properties can be enhanced with the use of rotational speed of 441 rpm, welding speed of 118 mm/min, and shoulder diameter of 17.5 mm. This is mainly due to very fine stir zone grain structure in the order of 5.5 μm and the presence of thin layer of banded structure at the advancing side of fabricated joints under optimum parameters.