Abstract
High manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automotive applications because of their exceptional properties of strength combined with an excellent ductility. However, the microstructure and properties of TWIP steels are affected by excessive thermal cycles, such as welding and heat treatment. This paper deals with characterization and understanding the effect of welding current and time on the mechanical properties and microstructure of the resistance spot welded TWIP steel. For this purpose, weld nugget diameter was evaluated and the hardness, tensile shear strength of the weldment, and failure mode of samples were also determined. It has been found that the tensile shear strength of the samples increased with increasing welding current and welding time without expulsion, which reduces the strength of the weldment. Tensile shear samples failed by a partial interfacial fracture mode for low-heat input welds. The pullout fractures were observed with a sufficient heat input without expulsion.
Highlights
There is an increasing demand for high strength steel sheets in the automotive industry in order to improve the fuel efficiency, occupant’s safety, and reduction of auto body weight [1]
Test results clearly point out that heat input is related to the welding current and welding time has an obvious effect on the tensile shear strength of the weldment, and there is a critical heat input level related to welding parameters with which the mechanical properties of the welded joint attain their optimum values
The results indicate that, except for 3 kA and 5 kA welding current for 20 cycles cycles of welding time and 7 kA welding current for five cycles of welding time, all of the of welding time and 7 kA welding current for five cycles of welding time, all of the combinations combinations of the welding process parameters in this study provide acceptable tensile of the welding process parameters in this study provide acceptable tensile strength for the strength for the automotive industry
Summary
There is an increasing demand for high strength steel sheets in the automotive industry in order to improve the fuel efficiency, occupant’s safety, and reduction of auto body weight [1]. Spena et al [10] carried out a preliminary study on the effects of the main important process parameters (welding time, welding current, and clamping force) on the mechanical and microstructural properties of resistance spot-welded TWIP sheets (with 22.4% Mn content) of 1.4 mm thickness with using the L-9(33 ) orthogonally array They noted that the tensile shear strength of the welded joints. Deformation behavior of high-manganese TWIP steels occurred earlier and high welding current increases the cracking tendency because of increasing has been widely studied in relation to microstructure and texture evolution by microscopy analysis nugget pressure and the tensile stress in heat affected zone (HAZ) during cooling [11]. Microstructure of welded samples are evaluated and tensile shear load bearing capacity, failure mode, and hardness distribution of weldment are determined for weld quality
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