Weldability study of dual phase and transformation induced plasticity automotive steels

Resistance spot welding studies at varying current with an 8 mm electrode on steel grades DP980, DP690, TRIP980 and TRIP780, established that peak strength sound weld could be achieved a range of 9 to 10 kA, where the nugget diameter was between 6.9 7.5 mm. The joint efficiency, measured as hardening ratio highest in TRIP690 2.22 for higher grade it 1.37 1.51. softening HAZ associated tempering preexisting martensite, 0.86 0.9. Higher fusion alloying content increased resistance pool enhanced hence strength. TRIP high cooling rate showed martensite retained austenite DP dispersed ferrite lower grade. Tensile shear lowest (16kN) DP780, while other is 20 22 kN. enhancement due current, partial pull out failure mode observed. At interfacial observed poor currents Coach peel 3.2 kN 2.2 2 690 1.7kN 980 follows trend TSS. may attributed microstructure austenite. steels low alloyed lath DP780 softer dispersion martensite. very currents, good but there influenced mode.