Microstructural analysis of weld nugget properties on resistance spot-welded advance high strength dual phase (α+α^/) steel joints

Abstract

This research work focuses on production of sound weld by Resistance Spot Welding (RSW) process and correlate the mechanical properties of Dual Phase (DP) steel joints with its microstructural features. The main application of resistance spot welding was used to build white body assembly in automotive industry. The welded joint recorded maximum value of 21.3 kN in TSFL and 18.3 kN in CTSFL. The Scanning Electron Microscope (SEM) and Optical Microscope (OM) of the Nugget Zone (NZ) revealed lath/needle like microstructures with effect of severe cooling rate. The TEM microstructure exposed the formation of martensite (α / ) in the Nugget Zone (NZ) and tempered martensite (Tα / ) in Heat Affected Zone (HAZ), which accounts for superior joint strength of DP lap shear joints. Furthermore, crystallography studies reported the phase composition and crystallinity in weldments as cementite and magnesium carbide in [101] and [200] indices that accounts for high hardness of 584 Hv in the weldments.

Effect of Silica Content on Mechanical and Microstructure Behaviour of Resistance Spot Welded Advanced Automotive TRIP Steels

“…Concerning the thickness of the sheets, an electrode with a 6 mm diameter was used. AWS D 8.9 standard was used to prepare the cast TRIP780 steel sheets for testing [22]. Figure 1 (b) showed the dimension of prepared specimens for testing.…”

“…The fractured specimens of the tensile shear and cross tensile tests were investigated to determine fracture types. TRIP 780 steel's mechanical behavior was studied using the tensile shear and cross tensile test as per AWS D8.9 standards [22]. Each test was repeated ve times and the mean value with error plot was reported.…”

Effect of Shielding Gas on the Properties of Stainless-Steel Sus 304l Plug Welded

“…The δ-ferrite phase is between the dendritic cells. The dendritic core structure is characteristic of the rapid solidification of the austenite phase during the smelting process [18]. Figure 8 shows the difference in grain size in the variation of welding current.…”

“…This causes a slow cooling rate. The faster the cooling rate or the decrease in temperature, the faster grain growth can stop [18]. Grain size affects the mechanical strength of the welding results, the larger the grain, the higher the tensile-shear load [19].…”