Title: Characterisation of microstructure, mechanical properties and fracture mode of the dissimilar joining of AISI 304 stainless steel and DP780 dual phase steel by resistance spot welding

Authors: Masoud Sabzi; Sadegh Moeini Far; Saeid Mersagh Dezfuli

Addresses: Department of Materials Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran ' Department of Mechanical Engineering, Islamic Azad University, Shushtar Branch, Shushtar, Iran ' Department of Materials Engineering, Islamic Azad University, Science and Research Branch, Tehran, Iran

Abstract: Microstructure, mechanical properties and fracture mode were investigated for the dissimilar joining of AISI 304 steel and DP780 steel by resistance spot welding. First resistance spot welding was utilised with a current density of 8 kA, holding time after welding of ten cycles and 5 kN electrode force. Then, to evaluate the microstructure, hardness profile and tensile-shear strength of weld nugget, scanning electron microscopy (SEM), Vickers micro-hardness and tensile-shear tests were carried out, respectively. Microstructural evaluations showed that in the dissimilar joining of DP780-AISI 304 stainless steel, fusion zone (FZ) microstructure was martensitic and some grains were also coarsened in heat affected zone (HAZ). Moreover, HAZ in AISI 304 stainless steel side remained completely austenitic, while HAZ in DP780 dual phase steel transformed to martensite. Micro-hardness results showed that in the dissimilar joint of DP780-AISI 304 stainless steel, FZ hardness was higher than base metals (BMs) of both sheets of steel. Additionally, HAZ in DP780 dual phase steel side had higher hardening ability than other joint areas. Results of tensile-shear tests of the dissimilar joint of DP780-AISI 304 stainless steel, indicated that the joint had the tensile-shear strength of 15 kN along with the occurrence of severe plastic deformation.

Keywords: resistance spot welding; DP780 dual phase steel; AISI 304 stainless steel; microstructure; hardness profile; tensile-shear strength.

DOI: 10.1504/IJMPT.2019.100819

International Journal of Materials and Product Technology, 2019 Vol.59 No.1, pp.3 - 15

Available online: 10 Jun 2019 *

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