CAMILA PUCCI COUTO
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Artigo IPEN-doc 29698 Effect of resistance spot welding parameters on the residual stress of automotive ultra high strength steel2017 - LARA, J.A.C.; COUTO, C.P.; NIZES, A.D.C.; ABBADE, L.; GONSALEZ, B.; COLOSIO, M.A.; ROSSI, J.L.Studies on residual stress effect in resistance spot welding (RSW) have not been widely explored for the new ultra-high strength steels (UHSS), such as, press-hardened steel (PHS) used for the automotive industry application. The number of PHS parts has been widely increasing in the vehicle structure, due to its ultra-high tensile strength achieved after the hot stamping process, which can reach 1500 MPa. This outstanding steel properties is function of steel grade and is a guaranty for lightweight and safety. Weldability is one of major issues to allow the large product application in the automotive industry however, the numbers of papers and works with focus on PHS weldability is still small. The residual stresses in spot welded joints play an important role in affecting the durability of the joint. It is well known that the residual stresses may reduce the mechanical properties of the welding joint and contribute to hydrogen embrittlement effect. This paper has undertaken an experimental survey of residual stress on 22MnB5 - PHS steel, using X-ray diffraction technique, before any heat treatment, i.e., without hot stamping, with variation of the main welding parameters. In general, it was found that the residual stress results showed a great influence of the resistance spot welding parameters. The residual stress measures showed levels up to 300 MPa in PHS material, which can impair the material usage.Artigo IPEN-doc 27004 Resistance spot welding characterization of press hardened steel2017 - ABBADE, L.; LARA, J.A.C.; COUTO, C.P.; GONSALEZ, B.; COLOSIO, M.A.; ROSSI, J.L.In the automotive industry the resistance spot welding (RSW) is one of the most used processes for joining steel sheets, being of fundamental importance the quality assurance of this process. In this work, 22MnB5 steel sheets for the hot stamping process, also known as PHS (Press Hardening Steel), were joined by the technique of resistance spot welding, so that the welding parameters were changed 16 times for the evaluation of the influence of these parameters on the mechanical properties. By conducting ultrasonic, tensile and hardness test, followed by metallography, it was possible to identify the characteristics of the spot weld effect on the material. The results of the tests performed in this work confirmed the difference in mechanical strength of the thermal zone (ZTA) in relation to the molten zone (ZF). For a certain set of the parameters it was shown a decrease in the strength of the ZTA and increasing to the weld point, which is demonstrated in the microstructural analysis and thus justifies the detachment of the weld button of the base material during tensile testing, i.e., there was a higher strength in the welded area.Resumo IPEN-doc 25337 Characterization of Al-Si coating on press hardening steel (PHS) submitted to a natural weathering test2018 - OLIVEIRA, B.G.; CUNHA, L.F.; ABBADE, L.; COLOSIO, M.A.; ROSSI, J.L.; COUTO, C.P.; LARA, J.C.; LIMA, V.F.Targeting the reduction of stamped sheet metal thicknesses, higher mechanical properties and better crash performance arise the hot stamping process as viable alternative. This is achieved by heating up a steel blank to approximately 900 ºC for the austenitization, soon after it is transferred to the hot stamping press, to be conformed and cooled, aiming a martensitic microstructure, After that, the finished part presents a tension strength about 1500 MPa. At the blank moving between furnace and press, oxidation occurs on the sheet metal surface, and Al-Si coating has been used as a good surface protection, which works against the oxidation process through a protection barrier. For corrosion analysis and a behavior evaluation of the coating subjected to climatic agents, the most trustful way is by means of the utilization of the natural weathering test, in the present case in an urban environment. It was used samples of 22MnB5 steel plates after different heat treatment conditions, achieving, in this way, weathering results based in technical standards obtained by means of light microscopy techniques.