Effects of Nb on Pitting Corrosion Resistance of Ni-Free FeCrMnCN-Based Stainless Steels

Abstract

The effects of Nb on grain refining and pitting corrosion behavior of Fe balance 18Cr10Mn0.3C0.3NxNb (x = 0-0.5 wt%) alloys were investigated through microstructure analysis, potentiodynamic polarization tests, and passive film analyses. As Nb content increased, the grain size decreased and the volume fraction of Nb(C,N) particles increased. The pitting potentials of the alloys increased as Nb content increased up to 0.2 wt%, but further addition of Nb caused a decrease in the pitting potential. On the grain-refined alloy with the addition of 0.2 wt% Nb, a thick and less defective passive film was formed resulting in the rise of the pitting potential. On the other hand, the decrease in the pitting potentials of the alloys with the addition of Nb more than 0.3 wt% Nb was primarily attributed to the increased volume fraction of coarse Nb(C,N) which provided initiation sites for pitting corrosion.

Investigation of the Localized Corrosion and Passive Behavior of Type 304 Stainless Steels with 0.2–1.8 wt % B

“…It is worth mentioning the decrease in the grain size of the austenite matrix of the BSSs as shown in Figure 2a-3–c-4. The grain refinement is known to accelerate passivation, resulting in the formation of a thick and dense passive film [29,30,31]; thus, the i passive is generally lowered when the grain size of the matrix decreases [32]. In this case, however, the i passive of the BSSs apparently increased although the grain size of the austenite matrix decreased; thus, it is reasonable to conclude that the change in the grain size is not the dominant factor for determining the magnitude of the i passive .…”

“…A notable difference among the passive films of the three BSSs was observed in the film thickness. The thickness of the passive film can be estimated from the concentration depth profile of O (Figure 9d) by taking the depth from the surface at which the 50% value of the O amplitude appears [31,33,34]. The thickness of the passive film formed on the B176 alloy was calculated to be 1.823 nm, while that on the B019 alloy was 2.469 nm.…”

Effect of Grain Size on the Pitting Corrosion Resistance of Lean Duplex Stainless Steel

“…The borate–phosphate–citric (BPC) buffer solution with a pH of about 8.5 was known to be helpful for forming a stable and thick passive film on Fe alloy. [ 17,39–41 ]…”

“…The borate-phosphate-citric (BPC) buffer solution with a pH of about 8.5 was known to be helpful for forming a stable and thick passive film on Fe alloy. [17,[39][40][41] The polarization tests were controlled by a potentiostat (Reference600, GAMRY Instruments). For the tests, a threeelectrode corrosion cell with a saturated calomel reference electrode (SCE), a Pt counter electrode, and the alloy sample that served as a working electrode was used.…”

Influence of nitrogen on corrosion behaviour of high nitrogen martensitic stainless steels manufactured by pressurized metallurgy

“…The corrosion resistance of stainless steels is remarkably affected by the chemical composition of passive films [10,40,47]. The increase of nitrogen content from 0.15 wt.% to 0.41 wt.% promoted the Cr enrichment in the passive film ( Fig.…”