Avaliação do comportamento microestrutural do aço 22MnB5 por meio da simulação física da zona afetada pelo calor do processo de soldagem a ponto por resistência

Abstract

Arising from the combination of tailored chemical composition and thermomechanical processing, advanced high strength steels (AHSS) provide an important balance between mechanical strength and weight reduction desired in automobiles. In this context, 22MnB5 steel stands out for offering mechanical strength levels around 1500 MPa in the hot-stamped condition, after quenching. Joining of components in the automotive industry, usually achieved by the resistance spot welding (RSW) process, continually demands technological improvements and optimization of parameters. These parameters influence not only the fusion zone, but also the heat-affected zone (HAZ), whose size generally depends on the chemical composition of the material, the thickness of the sheet and the heat input of welding, while microstructural changes depend, above all, on the combination of peak temperature and cooling rate. This combination results in the division of the HAZ into subcritical, intercritical, fine-grained supercritical and coarse-grained supercritical sub-regions. Considering the uncertainties related to the behavior of the HAZ, physical simulations using the Gleeble® platform has been a great ally, since it allows the reproduction of large-scale processes in laboratory-scale replicas, in addition to enabling the individual reproduction of enlarged sub-regions which, in a real spot weld, present themselves in a micrometric scale. With the objective of investigating these sub-regions, the present work aims to evaluate the suitability of the Gleeble® platform for reproduction, through physical simulation, of the corresponding thermal cycles from the resistance spot welding process of 22MnB5 steel. Parameters were defined based on literature-compiled data. Then, metallographic and microhardness tests were performed to assess the suitability of parameters to reproduce typical sub-regions of spot-welded 22MnB5 steel. Results show that the presented methodology can bring benefits to the reproduction, parameterization and prediction of sub regions of the HAZ, since microstructural responses after physical simulation correspond well to those observed in the real process. Furthermore, the technical feasibility study suggests a potential gain for the automotive industry by the use of the proposed methodology.