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http://dx.doi.org/10.3365/KJMM.2011.49.12.967

The Effect of Paint Baking on the Strength and Failure of Spot Welds for Advanced High Strength Steels  

Choi, Chul Young (School of Materials Science and Engineering, Pusan National University)
Lee, Dongyun (Department of Nano Fusion Technology, Pusan National University)
Kim, In-Bae (School of Materials Science and Engineering, Pusan National University)
Kim, Yangdo (School of Materials Science and Engineering, Pusan National University)
Park, Yeong-Do (Department of Advanced Materials Engineering, Dong-Eui University)
Publication Information
Korean Journal of Metals and Materials / v.49, no.12, 2011 , pp. 967-976 More about this Journal
Abstract
Conventional fracture tests of resistance spot welds have been performed without consideration of the paint baking process in the automobile manufacturing line. The aim of this paper is to investigate the effect of the paint baking process on load carrying capacity and fracture mode for resistance spot welded 590 dual phase (DP), 780DP, 980DP, 590 transformation in duced plasticity (TRIP), 780TRIP and 1180 complex phase (CP) steels. With paint baking after resistance spot welding, the l-shape tensile test (LTT) and nano-indentation test were conducted on the as-welded and paint baked samples. Paint baking increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial interfacial fracture (PIF) to button fracture (BF). Improvement in fracture appearance after LTT is observed on weldments of 780 MPa grade TRIP steels, especially in the low welding current range with paint baking conditions. The higher carbon contents (or carbon equivalent) are attributed to the low weldability of the resistance spot welding of high strength steels. Improvement of the fracture mode and load carrying ability has been achieved with ferrite hardening and carbide formation during the paint baking process. The average nano-indentation hardness profile for each weld zone shows hardening of the base metal and softening of the heat affected zone (HAZ) and the weld metal, which proves that microstructural changes occur during low temperature heat treatment.
Keywords
advanced high strength steels; resistance spot welding; paint baking; nano-indentation; fracture behavior;
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Times Cited By SCOPUS : 1
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