Investigation of forming limit curves and mechanical properties of 316 stainless steel/St37 steel tailor-welded blanks produced by tungsten inert gas and friction stir welding method

Abstract

The conventional welding method for joining dissimilar steels is the manual tungsten inert gas (TIG) method. Nevertheless, recently the benefits of solid state welding have been attracted attention of industrial manufacturers. In this article, TIG and friction stir welding method are compared based on the formability and mechanical properties of the welded sheets. Experimental evaluation of mechanical properties and forming limit curves have been carried out using uniaxial tensile test and Nakazima test, respectively. Results of experimental tests illustrated that formability of friction stir welded sheets was about 38% higher than the TIG-welded sheets. The microstructure analysis of TIG welded blanks revealed that grain growth in the heat-affected zone on the St37 steel, reduced the formability of welded joints in this method. Finite element simulation was used to estimate the forming limit diagram of the joints without considering the effects of welding heat on the material properties. The difference between the results of the FSW and finite element simulations was about 6%. While in the TIG welded blanks formability reduces significantly and difference between the result of experiment and simulation is about 33%. These results show that friction stir welding could more effectively preserve the sheets' formability after welding.