Welding of fine-grained steels for automotive applications

H. G. SVOBODA, M. N. RAMINI DE RISSONE, E. S. SURIAN Y L. A. DE VEDIA

Buenos Aires, Argentina

Conferencia; New Developments on Metallurgy and Applications of High Strenght Steels International Conference; 2008

Techint

Plain carbon steel sheets find a great number of applications, particularly in the automotive industry, where they must present a balance between high mechanical resistance, good conformability and weldability. These properties can be reached through the use of fine-grained steels. However, these materials may present grain growth and phase transformations in the heat affected zone during welding, which can impair the performance of these steels. In this work, the weldability, microstructure, and mechanical properties of thin gage grain refined steel sheets for structural components in the automotive industry were studied. Cold rolled 1mm thick sheets corresponding to three compositions: one of the plain C-Mn system and the other two Nb and Nb-Ti bearing respectively, were butt welded using the Gas Metal Arc Welding process with different transfer conditions (conventional short circuit, double pulsed arc and controlled short circuit) and Plasma Arc Welding. Weldability was assessed in terms of operational performance. The macrostructure and microstructure of the welded joints were analyzed on transverse cross sections. Tensile and Olsen tests were performed on the welded joints and microhardness profiles were obtained. It was found that the Nb-Ti bearing steel sheet presented a larger sensitivity to the welding process parameters, giving rise to defects in the welded joint. The other two sheets presented good operational behavior. Plasma Arc Welding welds presented the best performance under the conditions fixed for this work.