The factor time at the formation and development of the passive layer in the atmosphere

Abstract

Passive layers on high alloyed chromium nickel steels protect the metal from corrosion. The protective effect of the passive layer, however, does not immediately exist after the final surface treatment. Some time is necessary to form the protective layer. The exposure conditions are also decisive for the formation and further development of the passive layer besides the surface treatment. Samples of different chromium nickel steels are pickled and active passivated before they are exposed under laboratory conditions and in outdoor climates at different locations. The state of the corrosion resistance of the surface is determined with electrochemical noise measurements after different exposure times. The decreasing activity of the surface with an increasing exposure time indicates the further formation process of the protective qualities of the passive layer. An index which quantifies the state of the surface at the time of the measuring is calculated from the measured potential and potential noise signals. With these results, the development of the passive layer can be assessed and the corrosion resistance of the metal can then be estimated.

Influence of Surface Treatments on the Pitting Corrosion of Type 304 Stainless Steel by Electrochemical Noise Measurements

“…Excluding additional passivation treatments, a certain time under atmospheric conditions is necessary for the stabilization of the passive film. Bierwirth, et al, [18][19] confirmed, by means of EN measurements carried out in 1 M NaCl solution at pH 3, that the protective effect of the passive layer formed on mechanically ground surfaces of Type 316 (UNS S31600) stainless steel depends strongly on the atmospheric conditions and the corresponding aging time. A passive layer aged at 50% of relative humidity stabilizes considerably slower than those aged at a relative humidity higher than 90%.…”

“…7 Preliminary surface treatments have not only a direct bearing on the surface appearance but also play a decisive role for future corrosion protectiveness of the stainless steel surface. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] Burstein and coworkers [8][9] pointed out, for instance, that the susceptibility of stainless steels to pitting corrosion in chloridecontaining solutions is affected significantly by the surface finish. According to the authors, transition from metastable pitting to stable pitting corrosion is affected by surface roughness because pit growth is controlled by the diffusion rate, which is governed by the pit geometry controlling the electrolyte composition into the pit.…”

“…A similar behavior was observed by Bierwirth, et al, on Type 316 stainless steel. [18][19] Since the protective effect of stainless steel surfaces achieved by passivation does not immediately exist after surface conditioning, the relevance of aging conditions, in special humidity, should absolutely be considered in practice to ensure the corrosion resistance of the surface at service conditions. Regarding this, it is likewise important to consider that the passive layer shall behave like a dynamic system also at service conditions.…”

Examination of the influence of heat treatment on the corrosion resistance of martensitic stainless steels

“…The typically applied surface treatments, such as grinding, polishing and blasting will not only determine the appearance and mechanical properties of stainless steel surfaces but also have an impact on the corrosion resistance [12]. For example, homogeneous surfaces with low roughness exhibit faster and more stable passive film formation with higher corrosion protection compared to rough surfaces under the same conditions [13][14][15].…”

Influence of microstructure and surface treatment on the corrosion resistance of martensitic stainless steels 1.4116, 1.4034, and 1.4021

“…Furthermore, other major influencing factors affecting the corrosion behavior are the surface treatment and relative humidity in the time before any corrosion investigation, which can have positive and negative effects . Tempering colors formed due to high mechanical load during surface treatment have a significant negative influence on passive film formation.…”