Effects of post-weld heat treatment on mechanical properties and microstructure of resistance spot–welded lightweight steel
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To improve the mechanical properties of resistance spot–welded 780-MPa-grade lightweight steel, post-weld heat treatment (PWHT) through the application of a second welding current and using a furnace was performed after resistance spot welding. It was not possible to obtain satisfactory mechanical properties of the weld through the application of a second welding current. In the case of the PWHT by a furnace, the required loads were satisfied when PWHT was applied at temperatures of less than 300 °C for more than 30 min, and at more than 300 °C for 15 min or more. Due to the softening of martensite by PWHT, the resistance to fracture progression during tensile test was increased, and mechanical properties could be improved.
KeywordsResistance spot welding Lightweight steel Post-weld heat treatment Tempered martensite Second welding current Furnace
This research was funded by the Technology Innovation Industrial Program funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea) (Development of Car Body Modularization Technology using Advanced Cold Forming and Welding Technologies of Low Density GIGA Grade Light Steel Sheets).
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