Resistance spot weldability of Fe66Cr16.5Ni14.1Si3.4 advanced high strength steel using D-optimal design of experiment method

Abstract

Using advanced high-strength steels in automobiles has created a new challenge to achieve acceptable welds. The present study evaluates the weldability of the new generation of advanced high-strength steels in the FeCrNiSi alloy group. Hence, utilizing the design of experiment (DOE), it was obtained how the parameters namely the welding current, welding time, and electrode force affect the final properties. Additionally, the acceptable range of parameters for achieving an acceptable weld nugget in terms of size and strength was obtained. Accordingly, the nugget size effects on mechanical properties, namely energy absorption capability, failure mode in tensile-shear test, and microhardness were evaluated. The parameters were statistically significant and showed a high degree of reliability (95%) in terms of nugget size. The range of acceptable parameters for 1 mm thick steel and type A electrode was 9–21 cycles for welding time, whereas for welding current were 4–7 KA, 5 to 6.5 KA, and 5.7 to 6.5 KA at 2, 3, and 4 KN electrode force, respectively. Due to the grain growth in the heat-affected zone (HAZ), the HAZ softening was observed in the microhardness profile. All samples demonstrated desired fracture mode due to the HAZ softening, the ductile austenitic microstructure, the absence of brittle phases, and easy nugget rotation in the tensile-shear test. By increasing the nugget diameter from 3 to 5.1 mm, the peak load and the energy absorption of the spot welds exceeded from 5.4 KN to 6.5 KN and from 10 to 31 J, respectively.