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RISS 인기검색어
- 검색키워드
- 저자 : Goutam Mukhopadhyay (검색결과 2 건)
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Gorti Janardhan,Kaushal Kishore,Goutam Mukhopadhyay,Krishna Dutta 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9
This study aims to investigate the influence of nugget diameter on tensile-shear and fatigue properties of the dissimilar resistancespot-welded joints of interstitial free and high strength niobium microalloyed steel sheets. The spot-weldings are doneat currents of 7 kA and 9 kA at welding time of 300 ms with electrode force of 2.6 kN. Fatigue tests are done at different loadamplitudes, considering the maximum tensile-shear load bearing capacity of the joints. The tests are interrupted before thefinal failure to understand the crack initiation and propagation paths. The study is supplemented by the microstructural anddetailed fractographic analyses. The results indicated that the fatigue strength of the spot-welds increased with a decrease innugget diameter. This could be attributed to the higher microhardness of heat affected zone (HAZ), presence of compressiveresidual stress and lower variation in thickness reduction on the IF steel side, welded at 7 kA. However, the tensile-shearload bearing capacity of the spot-welds increased with increase in the nugget diameter. The failure of the spot-welded jointunder static loading initiates from the HAZ/base metal interface of the IF steel side. Nevertheless, under cyclic loading crackinitiates from the notch root at the interface of two sheets lying in the HAZ of IF steel side. Fractographic investigationsindicate intergranular fracture features in combination with striations, secondary cracks on the IF steel side under cyclicloading. Fracture surfaces of the specimens failed under static loading shows however, shear dimples on the IF steel side.
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Kaushal Kishore,Pankaj Kumar,Goutam Mukhopadhyay 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.4
Galvannealed (hot dip galvanized and annealed) dual phase (DP600) steel and interstitial free (IF) steel are two of the widelyused materials in automotive industries owing to their high specific strength, toughness, formability and corrosion resistance. This inevitably requires their joining to form larger components. Resistance spot welding has emerged as the predominantwelding technique for joining of sheet metals in automotive industries. There are complexities regarding microstructuralvariation of the fusion zone and across heat affected zones during spot welding of fundamentally dissimilar steels. This isfurther aggravated by the prospect of zinc redistribution during the welding process. Current study presents the evolution ofmicrostructure in different zones of welding in IF and DP600 steel. Micro-hardness profiles and electron back scattered diffractionstudies were performed. Furthermore, redistribution of elements in different welding zones is studied using electronprobe micro analysis. The effect of welding current and time on the nugget size and the strength of the weld during tensile–shear is determined. It was observed that there was an increase in nugget diameter and maximum load bearing capacity ofthe joint with an increase in heat input, until the occurrence of expulsion. Furthermore, critical nugget diameter for pull-outfailure was determined and existing empirical models were verified for the applicability in this case. None of the existingempirical models could predict the critical nugget diameter correctly and thus a new empirical relationship between sheetthickness and critical nugget diameter for zinc coated dissimilar steels has been proposed. Failure behaviour of the spotweldedsheets were studied under tensile–shear configuration under quasi-static and fatigue mode of loading and it showedsubstantial difference in location of crack initiation and fractographic features. Tensile–shear specimen at optimum weldingparameter failed from the base metal of the IF steel side with dimples on the fracture surface, whereas fatigue specimenfailed from the heat affected zone of the IF steel side with transgranular striations on the fracture surface.
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