Effect of nitrogen on the corrosion behavior of austenitic stainless steel in chloride solutions

doi:10.1016/j.matlet.2005.05.063

Materials Letters

Volume 59, Issue 26, November 2005, Pages 3311-3314

https://doi.org/10.1016/j.matlet.2005.05.063 Get rights and content

Abstract

The effect of partial replacement of nickel with nitrogen on the mechanism of localized corrosion resistance and repassivation for nitrogen-bearing stainless steel was investigated using anodic potentiodynamic polarization technique. The solutions used for this study contained 0.0, 0.05 and 0.33 M Fe³⁺ for solutions I, II and III, respectively, in a total Cl⁻ ion concentration 1 M. The pitting attack was found to be retarded by nitrogen addition and the samples were able to passivate as the nitrogen increase. Addition of nitrogen allows the decrease in the wt.% of Ni, but to a certain limit. Nitrogen is adsorbed on the interface of the metal oxide and results in the repulsion of Cl⁻ ions. Moreover, it reacts with H⁺ ions in the solution leading to higher pH, which explains the retardation effect of nitrogen to corrosion.

Introduction

Nitrogen is considered an important alloying addition to austenitic stainless steel in terms of corrosion resistance. It promotes passivity, widens the passive range in which pitting is less probable, improves stress corrosion cracking resistance in some media, and enhances the resistance to intergranular corrosion [1], [2], [3], [4], [5]. Moreover, nitrogen dissolved in austenitic stainless steel was found to increase its strength [6], [7]. The following mechanisms have been suggested to explain how nitrogen operates: (1) nitrogen in solid solution is dissolved and produces NH₄⁺, depressing oxidation inside a pit [1], [6], [8], [9]; (2) concentrated nitrogen at the passive film/alloy surface stabilizes the film, and prevents attack of anions (Cl⁻) [10], [11], [12], [13]; (3) produced nitrate ions improve the resistance to pitting corrosion [14]; (4) nitrogen addition stabilizes the austenitic phase [15]; and (5) nitrogen blocks the kink, and controls the increase of electric current for pit production [16].

In order to develop a resources-saving stainless steel with excellent localized corrosion resistance, 2 key technologies were adopted. The first key is high nitrogen alloying. Nitrogen enrichment improves pitting and crevice corrosion resistance without increasing chromium or molybdenum content. Therefore, adding nitrogen may contribute to reduce necessary chromium and molybdenum content. Moreover, as nitrogen is austenite former, adding nitrogen lowers the nickel content required for forming a single austenitic phase. Lowering the nickel in stainless steel lowers the costs of production. The aim of this paper is to study the effect of partial replacement of nickel with nitrogen on the pitting corrosion behavior of austenitic stainless steel.

Section snippets

Experimental

The chemical composition of the samples is described in Table 1. The samples were prepared, cold worked, and normalized by Steel laboratory (CMRDI). Austenitic stainless steel (sample 1) was used as the blank material for all the samples. In samples 2–5 the nitrogen content was gradually increased while the nickel content was gradually decreased.

Corrosion in 1 M NaCl

Fig. 1 shows potentiodynamic polarization curves for different samples of nitrogen stainless steel in 1 M NaCl solution at 25 °C. Sample 1, where there is no nitrogen and the nickel is 8.56 wt.%, the curve indicates anodic dissolution, the Cl⁻ ions prevent passivation to occur. In samples 2–5, where some percentages of nitrogen are added at the same time the percentages of nickel are decreased, there is a general tendency for passivation. The break in the current as the potential increases

Conclusions

1.
The pitting attack was found to be retarded by nitrogen addition and the samples were able to passivate as the nitrogen content is increased.
2.
Addition of nitrogen allows the decrease of the wt.% of Ni, but to a certain limit.
3.
The presence of a critical value of nitrogen and nickel lowers the general corrosion of the stainless steel in presence of Fe³⁺ ions, but almost has no effect in 1 M NaCl.

Acknowledgment

The author expresses her thanks and gratitude to all members in Steel Laboratory of CMRDI for supplying the materials. Special thanks are due to Prof. Dr Kamal Abd-Rabbo and Said Nabil.

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Effect of nitrogen on the corrosion behavior of austenitic stainless steel in chloride solutions

Abstract

Introduction

Section snippets

Experimental

Corrosion in 1 M NaCl

Conclusions

Acknowledgment

Corros. Sci.

Corros. Sci.

Corros. Sci.

Surf. Sci.

Corrosion

Corros. Eng.

Br. Corros. J.