Experimental analysis of spot welded parameters on tensile behavior of ferrite-martensite dual phase steel with Taguchi statistical method

In this paper, we show how Ferrite- martensite steel are produced by annealing operation, meanwhile tensile behavior of resistance spot weld and the effects of the resistance spot welding parameter and tensile failure modes in this type of steel will be examined. Design experiments was done by Taguchi statistical method and because of the number of studied parameters and factors, we choose L8 array. Parameters which could be controlled in resistance spot welding include welding time, the electrical current through the electrodes and the pressure that here considered as factors affecting the operation and tensile strength welded factor is examined as a test answer. In order to predict the optimal parameters of the resistance spot welding, signal to noise ratio is used in Taguchi statistical method. Generally, spot weld failure occurs in two modes: interfacial and pullout. The results show that by increasing the diameter of the weld nugget, pullout failure and the pullout with tear sheets becomes more likely to happen. Results of Taguchi statistical method also shows that the impact of the electrical current parameter of the spot welding machine compared to other properties was higher and it is less effective with increasing current. As well as SEM images of weld fracture surfaces have been taken and the results indicate ductile fracture in pullout mode and cleavage in interfacial mode of fracture.