Comparison of microstructural and mechanical properties of friction stir spot welded ultra-high strength dual phase and complex phase steels

Journal Article · Tue May 15 00:00:00 EDT 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2018.03.022· OSTI ID:22804992

Das, Hrishikesh; Mondal, Mounarik; Hong, Sung-Tae ^[1]; Lim, Yeongseok ^[2]; Lee, Kwang-Jin ^[2]

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1. School of Mechanical Engineering, University of Ulsan, Ulsan (Korea, Republic of)
2. Environment Materials and Components Center, Korea Institute of Industrial Technology (Korea, Republic of)

Highlights: • The microstructure and mechanical properties of FSSW of ultra high strength DP and CP steels are compared. • The stir zone (SZ) of CP steel mainly consists of bainite and martensite; no bainite is identified in the SZ of DP steel. • The cooling was not fast enough for the CP steel to suppress the effect of chemical composition on phase transformation. - Abstract: The microstructure and mechanical properties of friction stir spot welding of ultrahigh strength dual phase (DP) and complex phase (DP) steels are compared based on the experimental results. For both DP and CP steels, FSSW joints are successfully fabricated using the same process parameter set. While the microstructure of joints are characterized in detail using scanning electron microscopy, electron back scattered diffraction, and transmission electron microscopy, the mechanical property of joints are evaluated by shear tensile tests. The result of the microstructural analysis shows that the stir zone (SZ) of CP steel mainly consists of bainite and martensite, while no bainite is identified in the SZ of DP steel. The existence of bainite in the SZ of CP steel suggests that the cooling rate, which is nearly identical for both CP and DP steels, was not fast enough to suppress the effect of the alloying composition, particularly that of Mn, on the phase transformation. The result of the present study contributes to the development of solid state joining process of the ultrahigh strength steels.

• OSTI ID: 22804992
• Journal Information: Materials Characterization, Vol. 139; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BACKSCATTERING
COMPARATIVE EVALUATIONS
ELECTRON DIFFRACTION
MICROSTRUCTURE
PHASE TRANSFORMATIONS
SCANNING ELECTRON MICROSCOPY
STEELS
TRANSMISSION ELECTRON MICROSCOPY
WELDED JOINTS