Passivity of Dual-Phase Carbon Steel with Ferrite and Martensite Phases in pH 8.4 Boric Acid-Borate Buffer Solution

Abstract

Passivity of a dual-phase carbon steel with ferrite and martensite phases was investigated in pH 8.4 boric acid-borate buffer solution. The corrosion potential of the dual-phase steel was higher than that of pure martensitic steel and lower than that of pure ferritic steel. In dynamic polarization measurements, the passivity-maintaining current of the dual-phase steel was an intermediate value of those of pure ferritic and martensitic steels. EIS revealed that both the charge transfer resistance and capacitance of the oxide film formed on the dual-phase steel were intermediate between those of pure ferritic and martensitic steels. Although the donor density in the oxide film of the dual-phase steel was similar to that of pure ferritic steel, it was smaller than that of pure martensitic steel. SECM showed that the passive film formed on the martensite phase of the dual-phase steel had better electronic conductivity than that of the passive film formed on the ferrite phase. These differences in local passivity of the dual-phase steel suggested that the passive film formed on the ferrite phase has better passivity but larger scattering of the property than that of the passive film on the martensite phase. The local passivity of the dual-phase steel was strongly dependent on the texture of the substrate material.

Passivity of Spring Steels with Compressive Residual Stress

“…One group has suggested that the low density of point defect causes high corrosion resistance. Extensive experimental results apparently agree with this opinion [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Other researchers have reported a high corrosion rate or a low corrosion resistance for the metals or alloys with passive films with low point defect density [38][39][40][41][42], corresponding to the results drawn from this work.…”

“…Therefore, the origin of such discordance is not yet known. Many of the reports included a proposition that the concentration of point defect would affect the stability of the passive film and hence the corrosion resistance but did not provide a mechanism supported theoretically [18,19,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38].…”

Properties of Passive Films Formed on Ferrite-Martensite and Ferrite-Pearlite Steel Microstructures

“…The donor densities of both FM and FP samples are on the order of 10 21 cm −3 . This order of magnitude is typical for disordered heavily doped passive films [5,9,18,21]. The donor density values have been calculated from the slopes in the more positive potential range, i.e., for E > −0.3 V. The donor densities of passive films are 2.4 ± 0.3 × 10 21 cm −3 for the FM and 1.49 ± 0.08 × 10 21 cm −3 for the FP sample.…”

“…The role of pearlite and martensite in combination with ferrite in two-phase steels on mechanical properties is understood relatively well [2,3]. However, their corrosion and passivity behaviour is not yet well understood [4,5]. This is mainly due to the complex interaction of the microstructural features-grain sizes, phase fractions, dislocation densities, crystallographic orientations, phase morphologiesdictating the properties of the passive layer of steels.…”

“…They reported a higher passive current density and smaller ionic/electronic resistance for the pearlite structure and related this behaviour to the differences between conductivities and phase structures of FeCO 3 and Fe 2 O 3 in the layer. With well-controlled microstructures, Yanagisawa et al [5] investigated the role of the martensite volume fraction of low-alloyed steels and model alloys that minimised the changes of the microstructural features other than martensite volume fraction. They reported that the barrier properties of passive film deteriorate with increasing martensite volume fraction of the substrate.…”