Effect of the Heat Input in the Mechanical and Metallurgical Properties of Welds on AHSS Transformed Induced Plasticity
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Effect of the Heat Input in the Mechanical and Metallurgical Properties of Welds on AHSS Transformed Induced Plasticity Steel Joined with GMAW Processes in the Automotive Industry Victor Lopez 1, Arturo Reyes1, and Patricia Zambrano2 1)
Corporación Mexicana de Investigación en Materiales S.A de C.V., calle ciencia y tecnología 790 Saltillo, México. 2) Universidad Autónoma de Nuevo Leon, Pedro de Alba s/n San Nicolas N.L, México. Email: [email protected]
ABSTRACT The effect of the heat input on the mechanical and metallurgical properties of the welds has been investigated in the heat affected zone (HAZ) of welds joined with gas metal arc welding (GMAW), using normal production welding parameters. The thermal effect in the HAZ of the welds is important for the optimization of the welding parameters used when weld transformed induced plasticity (TRIP) steels, because this will have a great influence in the mechanical and metallurgical properties of the weld. In this work 3 samples was welded a high, average and low heat input, with the variation of welding parameters to obtain different thermal affectation to investigate the variations in different parts of weld joint: weld, HAZ and base metal, due the heat applied for the welding process used. Mechanical properties were evaluated by tension test, microhardness and fatigue testing and metallurgical evaluation with optical metallograpy, scanning electron microscopy (SEM), fractograpy and X-Ray diffraction (XRD).The results obtained shows that the mechanical properties of the tension test decrease when the heat input increase and the microhardness exhibit a softening zone in the HAZ with lower hardness and the fatigue life were similar for all heat inputs for the high stress levels, but only in low stress there is a difference. For metallurgical properties the metallographic evaluation shows ferrite, bainite martensite and retained austenite, and the fractography analysis exhibit a ductile fracture in all cases and the content in volume fraction of retained austenite increases in the HAZ of welds when increasing heat input in to the base metal due the thermal effect. KEYWORDS: joining, microstructure, fatigue, hardness, optical metallograpy. INTRODUCTION Due to high demand in energy saving, safety and reduction of pollutant emissions in cars, advanced high strength steels (AHSS) have become very attractive materials for use in the automotive industry. The weldability of transformation induced plasticity steels (TRIP) is a technical challenge for its use in the manufacture of automotive components, especially when the performance of these structures welded must meet high quality and safety requirements [1]. The gas metal arc welding process (GMAW) is commonly used in the automotive industry for joining conventional steels, however advanced TRIP steel does not offer this same facility as the mill steel to be welded; control of the welding parameters is critical in order to avoid the thermal effect of the welding process used, because cause microstructural changes in the
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