Pitting Corrosion of 18Cr-8Ni Stainless Steel

Effects of alloying elements on the pitting corrosion resistance of 17Cr-16Ni steels with and without 4% Mo were evaluated by the corrosion rate in 10% FeCl3.6H2O and 4% NaCl added with hydrogen peroxide and by the polarization measurement in 0.1N NaCl+0.1-0.25N Na2SO4 at 40C.The elements, the content of which was varied, were carbon, nitrogen, silicon, phosphorus, sulfur, manganese and nickel. The supplementary alloying elements were aluminum, titanium, vanadium, cobalt, copper, zirconium, niobium, tin and tungsten. Tungsten, like silicon, was found beneficial in minimizing the pitting corrosion if added together with molybdenum.Carbon was favorable if no chromium carbides were formed. Copper added to the Mo-free steel was beneficial, but not effective in the Mo-bearing steel. Manganese was proved to be harmful in both Mo-free and Mo-bearing steels, but increasing its content more than that of ordinary stainless steels did not enhance its harmful effect. The very favorable effect of nitrogen was also recognized. The effects of the other alloying elements are summarized in a table. The more noble the electrode potential at a relatively high c.d., i.e. 10mA/cm2, in anodic polarization curves measured in sodium chloride solution, the lower was the corrosion rate in the ferric chloride test if a second phase was absent. The presence of a second phase increases especially the corrosion rate in ferric chloride solution. It was indicated that the alloying to increase the passivating ability of the steel would shift the pitting potential to the more noble direction by passivating the depassivated sites before they can grow as ordinary pits.

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“…[3][4][5][6][7][8] The qualitative data in 4% NaCl added with hydrogen peroxide are given in this table. 4.…”

Section: Methodsmentioning

confidence: 99%

Effects of Alloying Elements on the Pitting Corrosion of Stainless Steels

Osozawa

Okato

Fukase

et al. 1975

Corrosion Engineering

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“…One of the main problems for pitting corrosion investigations is its stochastic initiation [5], which despite numerous works is not totally understood and for which several initiation mechanisms [6] and different possible initiation sites [7][8][9][10][11] have been proposed. This is the reason why the study of pitting corrosion by simply adding an aggressive anion, such as chloride ion, to the electrolytic solution is an intricate problem: it leads for full-immersion conditions to the simultaneous formation of several pits at different stages of development on the material surface, thus making any pitting analysis of this stochastic phenomena very difficult [12;13].…”

Section: Introductionmentioning

confidence: 99%

On the Propagation of Open and Covered Pit in 316l Stainless Steel

Heurtault

Robin

Rouillard

et al. 2016

Electrochimica Acta

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Pitting corrosion on stainless steel has been widely studied during the last decades, but since it is a stochastic process, it remains difficult to analyze experimentally such a phenomenon. In this work, reproducible single pits were performed on 316L steel by using an experimental setup based on the use of a glass microcapillary to locally supply chloride ions on the steel surface in order to characterize the pit propagation. This original approach allowed obtaining new results about pit propagation. Indeed, it was possible to control the presence of a metallic cap recovering the pit by adjusting the experimental parameters (potential -chloride to sulfate ratio -temperature). The presence of this cover was shown to be an important issue concerning the propagation mechanism.It was also possible to study the evolution of both the pit depth and the pit diameter as a function of various parameters. Then, based on the simulation of the current densities at the pit bottom and at the pit aperture, a special attention has been paid for the investigation of the local propagation mechanism.

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“…The passive film of stainless steels is made up of adsorbed oxygen. In the presence of chloride ions the higher affinity of oxygen allows for displacement of chloride ions, however as the alloy potential becomes more positive and chloride ions displaces the oxygen atoms and diffuse to the metal/oxide layer [13][14][15][16][17][18][19][20]. The chloride ion diffusion is due to electrostatic attraction.…”

Section: Pitting Corrosion Mechanism In the Presence Of Chloridesmentioning

confidence: 99%

Pitting Corrosion Resistance and Inhibition of Lean Austenitic Stainless Steel Alloys

Loto¹

2017

Austenitic Stainless Steels - New Aspects

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The pitting corrosion behavior of 301, 304 and 316 austenitic stainless steels in 2M H 2 SO 4 at 0-1.5% NaCl concentrations was investigated through potentiodynamic polarization and optical microscopy analysis. Electrochemical analysis of the pitting corrosion inhibition and surface protection properties of rosemary oil and aniline on the stainless was also performed. The corrosion rate, pitting potential, passivation potential, metastable pitting potential and surface morphology of both steels where significantly altered by changes in chloride concentration, differences in alloy composition and metallurgical properties of the steels. 316 steel had the lowest corrosion rate and highest pitting corrosion resistance followed by 301 steel. The surface morphology of 316 steel was slightly altered at 1.5% NaCl concentration while 301 steel appears to etch with grain boundaries appearing at higher chloride concentration. 304 steel showed no resistance to pitting after 0% NaCl coupled with relatively significant increase in corrosion rate values. Its surface morphology showed the presence of corrosion pits with respect to chloride and inhibitor concentration. Rosemary oil and aniline significantly reduced the corrosion rates values of the stainless steels and with consequent increase in their pitting corrosion resistance; however the compounds had no positive influence on the pitting corrosion behavior of 304 steel.

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Pitting Corrosion of 18Cr-8Ni Stainless Steel

Cited by 187 publications

References 20 publications

Effects of Alloying Elements on the Pitting Corrosion of Stainless Steels

Effects of Alloying Elements on the Pitting Corrosion of Stainless Steels

On the Propagation of Open and Covered Pit in 316l Stainless Steel

Pitting Corrosion Resistance and Inhibition of Lean Austenitic Stainless Steel Alloys

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