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Metallurgical characteristics and failure mode transition for dissimilar resistance spot welds between ultra-fine grained and coarse-grained low carbon steel sheets

Khodabakhshi, F ; Sharif University of Technology | 2015

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  1. Type of Document: Article
  2. DOI: 10.1016/j.msea.2015.04.019
  3. Publisher: Elsevier Ltd , 2015
  4. Abstract:
  5. We studied the microstructure and mechanical characteristics of spot welded specimens, fabricated from low carbon steel sheets with different microstructures. Both ultra-fine grained (UFG) steel sheet and coarse grained (CG) steel sheet were used. The refined microstructure of the UFG steel has been produced by severe plastic deformation (SPD) using the constrained groove pressing (CGP) method. The grain size of the base metals was approximately 260. nm and 30. μm in diameter, respectively, in the UFG and CG steels. Examining the microstructure of a cross section cut through the spot weld reveals a similar grain size and phase distribution in the nugget on both the sides of the initial interface between sheets. Some recrystallization is observed in the heat affected zone on the UFG side as previously reported after the welding of symmetrical UFG-UFG spot welded specimens. The same energy deposit produces larger nuggets after the spot welding of UFG steels. Moreover, the hardness distribution across the nugget changes after welding on both sides of the initial (UFG/CG) interface. This effect is presently attributed to a change in the solidification, cooling rate and tempering after welding, likely because the higher resistance of UFG steel sheets increases the heat release by the Joule effect during spot welding. These changes in the mechanical behavior modify the transition between the interfacial failure (IF) and pull out failure (PF) mode with respect to energy deposit
  6. Keywords:
  7. Coarse-grain ; Aluminum sheet ; Carbon ; Deposits ; Failure (mechanical) ; Grain size and shape ; Heat affected zone ; Heat resistance ; Microstructure ; Plastic deformation ; Resistance welding ; Spot welding ; Steel metallurgy ; Steel sheet ; Welding ; Welds ; Coarse grains ; Dissimilar joining ; Resistance spot welding ; Severe plastic deformations ; Ultra fine grain ; Low carbon steel
  8. Source: Materials Science and Engineering A ; Volume 637 , 2015 , Pages 12-22 ; 09215093 (ISSN)
  9. URL: http://www.sciencedirect.com/science/article/pii/S0921509315004165