RESEARCH OF THE BEST TECHNOLOGICAL AND METALLURGICAL PARAMETERS FOR PERFORMING THE ELECTRIC RESISTANCE WELDING OF LOW CARBON STEELS
AbstractThis work deals with the research of the optimal technological and metallurgical parameters in order to implement a reliable procedure for the electric resistive welding of low carbon structural steel, in order to evaluate the conditions which can grant the best mechanical performances. Low carbon steels must be featured by high plastic formability properties, since the production process consists in the piping of a rolled band, followed by an Electric Resistance Welding (ERW) of the edges. The optimal technological parameters have been identified performing welding tests at several levels of electric power, squashing length and forward velocity of the pipe along the coil axis. Several mechanical tests have been performed for the determination of the properties of the materials under examination, in order to characterize the main mechanical properties, i.e. Young modulus, yield and the ultimate stresses, yield point elongation (the strain after which the plastic behaviour takes place), anisotropy coefficients (rm, ?r), Vickers micro-hardness and hardening coefficient of the materials analysed, while the residual stress induced in correspondence of the welded joining have been determined by X-ray diffraction. The microstructural characteristics of the steels have been obtained through micrographic analyses coupled with the use of Electron Back Scattered Diffraction techniques (EBSD). The value assumed by the hardening coefficient and by the yield elongation point has been revealed to be a strongly significant parameter for assuring the quality of the joining in order to avoid a very early formation of the cracks in the welding region.