CAMILA PUCCI COUTO

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Effect of resistance spot welding parameters on the residual stress of automotive ultra high strength steel
2017 - 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.
The hot-stamping effect on the corrosion properties of the 22MnB5 steel coated with hot-dip aluminum-silicon assessed by a salt spray test and Raman spectroscopy
2022 - COUTO, CAMILA P.; BAERT, KITTY; COSTA, ISOLDA; PANOSSIAN, ZEHBOUR; DE GRAEVE, IRIS; TERRYN, HERMAN; ROSSI, JESUALDO L.; REVILLA, REYNIER I.
The effect of hot stamping on the corrosion properties of boron-manganese 22MnB5 steel coated with hot-dip aluminum-silicon was evaluated under severe conditions by a continuous salt spray test (SST). The corrosion mechanism changed from localized to generalized, as cathodic precipitates were not present after hot stamping. Intrinsic defects in press-hardened steel samples were the reason for severe damage in both metallic coating and steel substrate under SST conditions. The red rust formed at the top surface, characterized as different iron-based compounds, is due to both the iron diffusion from the steel substrate toward the surface and the corrosion of the steel substrate.
Influence of hot-stamping process on the corrosion initiation and properties of corrosion products at the surface of 22MnB5 steel metallic coated with hot-dip Al-Si
2021 - COUTO, CAMILA P.; BAERT, KITTY; COSTA, ISOLDA; PANOSSIAN, ZEHBOUR; DE GRAEVE, IRIS; REVILLA, REYNIER I.; TERRYN, HERMAN; ROSSI, JESUALDO L.
22MnB5 is an ultra-high strength steel combined with hot-stamping process, also known as press hardened steel (PHS). It is a strategic material for the automotive industry because it allows safety improvement, lightweight design and consequently reduction of fuel consumption. In order to prevent surface scale and steel decarburisation during the hot-stamping process, the material is often protected with metallic coatings. Hot-dip Al-Si (Si 10 % in mass fraction) is the most used system for hot-stamping application. This study has the objective to characterize the corrosion initiation and the properties of the corrosion products at the surface of samples before and after hot-stamping process. The samples were submitted to several cycles of accelerated corrosion tests in a salt spray chamber. A systematic characterization of the corroded surface was done by means of Raman spectroscopy and scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM - EDS). The samples were also immersed in a Cl– containing solution, after which the morphology of the corrosion attacks and the corrosion initiation process were studied. The thermo-mechanical process changes the corrosion mechanism as well as the nature of the corrosion products.
Influence of austenitisation temperatures during hot stamping on the local electrochemical behaviour of 22MnB5 steel coated with hot-dip Al-Si
2021 - COUTO, CAMILA P.; REVILLA, REYNIER I.; POLITANO, RODOLFO; COSTA, ISOLDA; PANOSSIAN, ZEHBOUR; GRAEVE, IRES de; ROSSI, JESUALDO L.; TERRYN, HERMAN
Scanning Kelvin probe force microscopy was used to evaluate the effect of austenitisation temperatures during hot stamping on the local electrochemical behaviour of 22MnB5 steel coated with hot-dip Al-Si. A variation in the austenitisation temperature around 50 °C substantially altered the coating morphology as well as the local electrochemical behaviour of the system (coating/steel). Both coating layer and steel substrate became nobler as the austenitisation temperature increased. The former was due to the overall iron enrichment while the latter was related to the microstructural transformation during quenching. Therefore, the driving force for cathodic protection decreased as the austenitisation temperature increased.
The effect of hot-stamping process on the local electrochemical behaviour of the 22 MnB5 steel coated with hot-dip aluminium-silicon
2021 - COUTO, CAMILA P.
Press-hardened steel (PHS) is a strategic steel for the automotive industry. The application of this type of steel in the vehicle structure allows safety improvement, mass reduction and less fuel consumption. Due to its ultra-high-tensile strength, the PHS components are produced by means of hot-stamping process. Hot stamping is a thermo-mechanical process in which a steel blank is heated at austenitisation temperatures and then is transferred to a press tool, where the material is formed and quenched simultaneously. The steel substrate is often protected with metallic coatings prior to hot stamping to avoid its oxidation and decarburisation. Zinc and aluminium based systems are often used as coatings for automotive applications. However, for hot stamping, the hot-dip aluminium-silicon (Al-Si) system is the most widespread and used. This coating presents good corrosion and oxidation resistance at high temperatures. However, during hot stamping, the initial microstructure and chemical composition of the metallic coating changes completely due to diffusion. These microstructural and compositional changes take place in the austenitisation step. Hence, after hot stamping the whole coating layer becomes a complex multi-layered system in which the sublayers are enriched in either aluminium or iron/silicon. Consequently, the coating properties, including the corrosion properties, also change after hot stamping. However, little is known about the effect of the morphological and compositional changes of the Al-Si coating due to the thermo-mechanical process on its corrosion behaviour and performance. The different sublayers in the coating form different micro-galvanic-couplings, which can affect the global electrochemical behaviour of the system. Therefore, a detailed approach based on local electrochemical techniques was suggested to evaluate the role that each sublayer plays on the electrochemical behaviour. This work aimed at evaluating the effect of the hot-stamping process on the electrochemical behaviour of 22MnB5 coated with hot-dip Al-Si (10 % Si in mass fraction). The morphology-composition of the layered structure was obtained using field emission scanning electron microscopy (FE-SEM) combined with energy dispersive X-ray spectroscopy (EDS). Global corrosion properties were evaluated by open circuit potential (OCP), linear sweep voltammetry (LSV) and accelerated corrosion test. Nonetheless, the effect of each sublayer of the coating-steel system, on the electrochemical behaviour was investigated on a local scale by two complementary techniques: scanning Kelvin probe force microscopy (SKPFM) and electrochemical micro cell. The former was carried out in the samples' cross-section and it shows high lateral resolution, while the latter was done from the top surface in a depth profile approach. Thus, it enabled the local potentiodynamic polarisation in an isolated sublayer. The results obtained during the implementation of this work highlight the high complexity of the Al-Si coating-steel system (composed of several layers), which in turn supports the need for local investigations. The morphology and composition of the coating were shown to be greatly influenced by the hot-stamping process (parameters) and this resulted in considerable variations of the local corrosion and electrochemical behaviour of the coating-steel system.
Depth profiling approach to evaluate the influence of hot stamping on the local electrochemical behaviour and galvanic series of hot-dip Al-Si coating on 22MnB5 steel
2021 - COUTO, CAMILA P.; ANDREATTA, FRANCESCO; LANZUTTI, ALEX; COSTA, ISOLDA; PANOSSIAN, ZEHBOUR; DE GRAEVE, IRIS; TERRYN, HERMAN; ROSSI, JESUALDO L.; REVILLA, REYNIER I.
The influence of hot-stamping process on the corrosion properties of Al-Si coating on 22MnB5 steel was locally evaluated using a depth profiling approach combining GDOES and electrochemical micro cell. The results highlight the complexity of the system and the high dependence of the local galvanic series on the hot-stamping process. Due to iron diffusion from the steel substrate into the coating, the Al-rich layers presented active behaviour, whereas the initial coating condition showed a passive behaviour. Conversely, Fe/Si-rich sublayers acted as protective barrier for the steel substrate, as they show passive behaviour with nobler corrosion potentials and lower current densities.
Electrochemical behaviour of 22MnB5 steel coated with hot-dip Al-Si before and after hot-stamping process investigated by means of scanning Kelvin probe microscopy
2020 - COUTO, CAMILA P.; REVILLA, REYNIER I.; COLOSIO, MARCO A.; COSTA, ISOLDA; PANOSSIAN, ZEHBOUR; DE GRAEVE, IRIS; TERRYN, HERMAN; ROSSI, JESUALDO L.
Press-hardened steels are commonly protected with hot-dip Al-Si coating. Due to the electrochemical complexity of this system, either before or after hot-stamping process, SKPFM was used to investigate the influence of the thermo-mechanical process on the electrochemical behaviour of the galvanic coupling. The hot-stamping process changed significantly the anodic/cathodic coupling of the coating/steel due to iron enrichment in the coating layer. Hence, a concurrent mechanism was thoroughly established, i.e., while the press hardening enhances the corrosion properties of the steel system (steel and metallic coating) through diffusion, at the same time it diminishes the cathodic protection of the Al-Si layer.
The use of scanning vibrating electrode technique to evaluate the effect of hot stamping on the corrosion resistance of 22MnB5 press-hardened steel electroplated with Zn-Ni
2019 - COUTO, CAMILA P.; COSTA, ISOLDA; VIVEIROS, BARBARA V.G. de; ALENCAR, MAICON C. de; COLOSIO, MARCO A.; PANOSSIAN, ZEHBOUR; ROSSI, JESUALDO L.
Carmakers must achieve the worldwide targets for lightweight materials, safety and reducing the fuel consumption. The use of press-hardened steel (PHS), in vehicle structures has been contributing with these requirements. This type of steel is widely used for the hot-stamping which consists in heating the steel blank to total austenitization temperature and then transferring it from the furnace into the die tool where the steel is formed and quenched at the same time. PHS is usually protect with metallic coatings in order to avoid both steel oxidation and decarburization. Hot-dip Al-Si coating is currently the main used in this application. However, alternative coatings, like zinc-based, are under investigation. This work aims at evaluating the corrosion resistance of the 22MnB5 grade PHS, electroplated with Zn-Ni, before and after hot stamping, using the scanning vibrating electrode technique (SVET). Results from SVET showed that samples prior to hot stamping, the corrosion mechanism was uniform over the exposed surface, and was mainly related to selective dissolution of zinc from the coating. On the other hand, hot stamped samples showed localized corrosion mechanism with decrease in current with time of immersion due to the formation of corrosion products on the exposed surface.
Resistance spot welding characterization of press hardened steel
2017 - 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.
Microstructural characterization of air quenched valve seat inserts obtained with AISI D2 tool steel
2017 - GOMES, M.P.; SANTOS, I.P.; COUTO, C.P.; BETINI, E.G.; COLOSIO, M.A.; ROSSI, J.L.
The obtention of valve seat insert (VSI) by powder metallurgy using a mixture of iron powder and tool steel is fulfilling the requirements for substitution of cobalt and lead in commercial parts, aiming cost reduction and avoid the lead toxicity. The aim of this work consisted of evaluate the influence of heat treatment on VSI obtained with AISI D2 tool steel powder. The AISI D2 tool steel powder was mixed with iron powder and additives such as manganese sulphide, zinc stearate, graphite and carbides. The heat treatment of the VSI consisted of air quenching followed by double tempering it at 500 °C. The microstructural characterization was performed using scanning electron microscopy and energy dispersive spectroscopy.

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