Dissimilar welding used in the automotive area are possible joints with the GMAW process; however, its structural performance must be evaluated. The focus of this work is to study the microstructural–mechanical properties of dissimilar welding DPC340Y590T dual phase–JSC270C low carbon steels. Microhardness profile, tensile, and impact tests were used to evaluate the mechanical behavior, while optical and scanning electron microscopy were employed to evaluate the microstructural changes. The tensile strength was 540 and 275 MPa in dual phase and low carbon, respectively. Weld thermal cycles were obtained by means of K type thermocouples. The welding heat input generated martensite and grain growth in the dual phase heat affect zone, while grain growth and perlite phase increased in the low carbon heat affected zone. The variation in microhardness profile was produced by the presence of different phases, and the temperature at the end of dual phase heat affect zone was approximately 242 °C. During impact tests, the absorbed energies were 19.3, 50.7, and 50.2 J for low carbon, dual phase steel, and the welded dissimilar joint respectively. Finally, dissimilar welding subjected to tensile test failed in the low carbon steel (270 MPa), out of the heat affect zone, thus a good dissimilar joint between both steels was obtained.
Dual phase (DP) steels have high strength, while maintaining outstanding elongation capacities. This is possible using a well-controlled thermomechanical process that produces a perfect phase combination in the DP microstructures. However, automotive makers are required to weld the DP steels, which generates a soft zone in the microstructure. In this work, 1.6 mm-thick DP980 steel sheets were welded by gas metal arc welding process to analyze the response of the welded soft zone to cyclic loading conditions. Conducted macrographic and metallography analyses revealed good quality in the appearance of the welded joints, with a complete fusion of the DP980 joint and without the presence of discontinuities. Low cycle fatigue tests of the DP welded joints were conducted under a constant amplitude strain control mode. The welded joints experienced a fatigue life reduction with respect to the DP980 steel of ~16% at strain amplitudes of 0.2, 0.3, and 0.4%. For strain amplitudes larger than 0.6%, the fatigue life of the welded joint was reduced by 39%. Weld thermal cycles combined with metallography analysis indicated that a tempered process of the martensite during the welding was responsible for the soft-zone formation and the poor fatigue response.
Las Herramientas de Mejora Continua (HMC) se han vuelto importantes en el ámbito laboral, ya que permiten analizar situaciones actuales, identificando los principales problemas que afectan la eficiencia en las empresas. En el caso de una empresa de telecomunicaciones se implementaron las HMC en el departamento automotriz, ya que presentaba una serie de inconsistencias, que ocasionaba una serie de reclamos, baja eficiencia en el departamento y gastos mayores en los mantenimientos correctivos. Algunas herramientas que se implementaron fueron el ciclo PHVA, diagrama de Pareto y diagrama causa-efecto. Lo anterior permitió identificar el problema raíz que afecta a la empresa, el cual radica en la falta de un adecuado programa de mantenimiento.
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