Avaliação das tensões residuais em chapas do aço microligado LNE380 destinadas ao processo de corte a laser

Abstract

In a dynamic work environment, the competitive advantage in the manufacturing industries comes from the constant searching for product and processes innovation. In the automotive industry, where the companies are challenge to balance mechanical performance and the cost of their products, the need for more productive and reliable processes implies in facing new obstacles regarding the consumption relations in the steel market. If the bargaining power controls the cost of the raw materials, it is a fact that the demand for cheaper steels will reflect in low quality products and processes. Taking into consideration that the reduction of production wastes depends on the quality of the raw materials, and that cost, mechanical performance and superficial quality can still be considered trade-offs, the following dissertation proposes the application of an experimental method. This method is an attempt to detect warping defects in LNE380 microalloyed steel sheets, which are used in laser cutting processes. Through an exploratory experimental search, the study makes use of two 9,50 mm thick sheets (A and B) in order to test the precision of the sectioning and indentation methods regarding to the evaluation of the thermomechanical hot rolling residual stresses. As a result of the application of the proposed methodology, it is possible to observe that the studied samples presented longitudinal compressive stresses in both of the experimental methods. While the sectioning practice showed stresses range from 12,69 to 63,39 MPa in B and from 43,73 to 73,27 MPa in A, the indentation method revealed the same stresses can vary from 142,29 to 155,83 MPa in A and from 122,80 to 147,04 MPa in B. Comparing these results to the real performance of the microalloyed steel in the laser cutting process, it is possible to conclude that the sectioning method is the most appropriate alternative to detect warping defects in the LNE380 steel sheets. In addition, the data also show that there is a large stress heterogeneity across the steel thickness (medium relative standard deviation of 42,02% for B and 52,23% for A) and a bigger probability of A reveal warping defects during the longitudinal laser cutting processes, due to its anisotropic condition. [resumo fornecido pelo autor]