ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleit... more ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleite was studied alone and in galvanic couple with zinc. Simonkolleite on steel inhibits cathodic oxygen reduction in 5 wt.% NaCl at pH = 7 and 9 but it is unstable at pH = 11. In NaCl solution the galvanic current density between Zn and steel is reduced by more than twice if the synthetic simonkolleite layer is deposited on steel. The polarity between Zn and steel is inverted after several hours in NaHCO3 solutions. X-ray diffraction confirmed the instability of simonkolleite in this conditions and its transformation into carbonate containing salts.
The reduction of the fuel consumption is one major topic for the car makers. One simple way to ac... more The reduction of the fuel consumption is one major topic for the car makers. One simple way to achieve this issue is to decrease the weight of the vehicles. Therefore the new generation of Advanced High Strength Steels (AHSS) is largely integrated in the modern car bodies. However, the sensitivity to delayed fracture induced by hydrogen is increased for such microstructures and a tensile strength above 1000MPa is considered as a potential risky level. In the present paper, potential impact of carmaking processes like forming, welding, cutting, painting is investigated using hydrogen measurements, carried out by Thermal Desorption Analysis (TDA), and delayed fracture tests performed on small specimens or self stressed welded components more representative of a real part. It is shown that, in the conditions of the tests, no delayed fracture occurs. In a second stage, the delayed fracture risk due to hydrogen by corrosion is evaluated with a methodology combining various techniques: ac...
ABSTRACT An improved corrosion resistance of aluminized press hardened steel Usibor® AlSi compare... more ABSTRACT An improved corrosion resistance of aluminized press hardened steel Usibor® AlSi compared to untreated 22MnB5 steel is observed in cyclic corrosion tests even though cracks are present in the coating after the hot stamping resulting in the simultaneous corrosion of the coating and the steel beneath. The coating shows a poorer performance in continuous salt spray test than in cyclic corrosion test. Electrochemical measurements and in situ measurement of the elemental dissolution rates combined with the characterization of the corroded surface are used to argue in favor of an anticorrosion mechanism related to the barrier protection by corrosion products formed. Al and Fe oxides were formed in continuous test and aluminosilicates and a mixture of hydroxides after the cyclic test. The formation of specific corrosion products is assumed to be due to a specific surface pH evolution during corrosion testing.
ABSTRACT Austenitic Fe-Mn-C steels are Ultra High Strength Steels which may be used for the produ... more ABSTRACT Austenitic Fe-Mn-C steels are Ultra High Strength Steels which may be used for the production of deep drawn automotive parts containing extremely high residual stress and strain levels. In consequence, hydrogen absorption occurring during the corrosion process in aqueous environments may enhance the sensitivity of these steels to different kinds of hydrogen-induced damage, in particular Stress Corrosion Cracking (SCC). In order to predict and prevent SCC, it is important to study the behaviour of hydrogen in these austenitic steels exposed to aqueous environments and in particular the dependence on the alloy chemistry and microstructure. SIMS profiles of deuterium introduced by cathodic charging in selected specimens were used to characterize the diffusion of hydrogen in these steels. This allowed to be studied the role of chemical composition and microstructure on the kinetics of H absorption at room temperature. The competition between bulk matrix diffusion and short-circuit diffusion phenomena along grain boundaries was investigated. The results show a strong dependence of H diffusion and distribution on the alloy chemistry and grain size.
ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleit... more ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleite was studied alone and in galvanic couple with zinc. Simonkolleite on steel inhibits cathodic oxygen reduction in 5 wt.% NaCl at pH = 7 and 9 but it is unstable at pH = 11. In NaCl solution the galvanic current density between Zn and steel is reduced by more than twice if the synthetic simonkolleite layer is deposited on steel. The polarity between Zn and steel is inverted after several hours in NaHCO3 solutions. X-ray diffraction confirmed the instability of simonkolleite in this conditions and its transformation into carbonate containing salts.
ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleit... more ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleite was studied alone and in galvanic couple with zinc. Simonkolleite on steel inhibits cathodic oxygen reduction in 5 wt.% NaCl at pH = 7 and 9 but it is unstable at pH = 11. In NaCl solution the galvanic current density between Zn and steel is reduced by more than twice if the synthetic simonkolleite layer is deposited on steel. The polarity between Zn and steel is inverted after several hours in NaHCO3 solutions. X-ray diffraction confirmed the instability of simonkolleite in this conditions and its transformation into carbonate containing salts.
The reduction of the fuel consumption is one major topic for the car makers. One simple way to ac... more The reduction of the fuel consumption is one major topic for the car makers. One simple way to achieve this issue is to decrease the weight of the vehicles. Therefore the new generation of Advanced High Strength Steels (AHSS) is largely integrated in the modern car bodies. However, the sensitivity to delayed fracture induced by hydrogen is increased for such microstructures and a tensile strength above 1000MPa is considered as a potential risky level. In the present paper, potential impact of carmaking processes like forming, welding, cutting, painting is investigated using hydrogen measurements, carried out by Thermal Desorption Analysis (TDA), and delayed fracture tests performed on small specimens or self stressed welded components more representative of a real part. It is shown that, in the conditions of the tests, no delayed fracture occurs. In a second stage, the delayed fracture risk due to hydrogen by corrosion is evaluated with a methodology combining various techniques: ac...
ABSTRACT An improved corrosion resistance of aluminized press hardened steel Usibor® AlSi compare... more ABSTRACT An improved corrosion resistance of aluminized press hardened steel Usibor® AlSi compared to untreated 22MnB5 steel is observed in cyclic corrosion tests even though cracks are present in the coating after the hot stamping resulting in the simultaneous corrosion of the coating and the steel beneath. The coating shows a poorer performance in continuous salt spray test than in cyclic corrosion test. Electrochemical measurements and in situ measurement of the elemental dissolution rates combined with the characterization of the corroded surface are used to argue in favor of an anticorrosion mechanism related to the barrier protection by corrosion products formed. Al and Fe oxides were formed in continuous test and aluminosilicates and a mixture of hydroxides after the cyclic test. The formation of specific corrosion products is assumed to be due to a specific surface pH evolution during corrosion testing.
ABSTRACT Austenitic Fe-Mn-C steels are Ultra High Strength Steels which may be used for the produ... more ABSTRACT Austenitic Fe-Mn-C steels are Ultra High Strength Steels which may be used for the production of deep drawn automotive parts containing extremely high residual stress and strain levels. In consequence, hydrogen absorption occurring during the corrosion process in aqueous environments may enhance the sensitivity of these steels to different kinds of hydrogen-induced damage, in particular Stress Corrosion Cracking (SCC). In order to predict and prevent SCC, it is important to study the behaviour of hydrogen in these austenitic steels exposed to aqueous environments and in particular the dependence on the alloy chemistry and microstructure. SIMS profiles of deuterium introduced by cathodic charging in selected specimens were used to characterize the diffusion of hydrogen in these steels. This allowed to be studied the role of chemical composition and microstructure on the kinetics of H absorption at room temperature. The competition between bulk matrix diffusion and short-circuit diffusion phenomena along grain boundaries was investigated. The results show a strong dependence of H diffusion and distribution on the alloy chemistry and grain size.
ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleit... more ABSTRACT Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleite was studied alone and in galvanic couple with zinc. Simonkolleite on steel inhibits cathodic oxygen reduction in 5 wt.% NaCl at pH = 7 and 9 but it is unstable at pH = 11. In NaCl solution the galvanic current density between Zn and steel is reduced by more than twice if the synthetic simonkolleite layer is deposited on steel. The polarity between Zn and steel is inverted after several hours in NaHCO3 solutions. X-ray diffraction confirmed the instability of simonkolleite in this conditions and its transformation into carbonate containing salts.
Uploads
Papers by C. Allely