doi: 10.11902/1005.4537.2016.041
Cr对Q420钢在高盐度大气环境下耐蚀性的影响

Effect of Cr on Corrosion Resistance of Q420 Steel in Atmosphere with High Salinity

Abstract:

Effect of Cr on the corrosion resistance of Q420 steels with different Cr content (2%, 5% and 9% mass fraction) in atmosphere with high salinity was investigated by means of weight loss test, XRD and SEM. The results show that corrosion resistance of Cr modified Q420 steels is higher than that of simple Q420 steel. Among others the Q420 steel with 9%Cr shows the lowest corrosion rate and the highest corrosion resistance. The curve of corrosion rate versus time of the simple Q420 steel kept stable within a high level. While the corrosion rate of Cr modified steels increases in the initial stage and then increases, which indicates that the rust scale became compact and stable in the later stage. It was revealed that Cr can promote the formation of α-FeOOH, which is a stable phase and makes the rust scale much compact and stable so that to act as an effective barrier for the transfer process of the corrosive species.

Key words: Q420 ; Cr alloyed steel ; high salinity atmospheric environment ; corrosion resistance ; α-FeOOH

1 实验方法

2 结果与讨论
2.1 腐蚀失重

$W = ( w 0 - w t ) × 10 6 2 t ( ab + bc + ac )$ (1)

$D = 10 - 3 W ⋅ t ρ$ (2)

$D = 10 3 × ( w 0 - w t ) 2 ρ ( ab + bc + ac )$ (3)

Fig.1 Corrosion rate (a) and corrosion thinning (b) of four steels during cyclic immersion test

2.2 锈层形貌观察

Fig.2 SEM images of Q420 (a, e), 2Cr (b, f), 5Cr (c, g) and 9Cr (d, h) steels after corrosion for 72 h (a~d) and 360 h (e~h)

Fig.3 Cross sections of rust layers formed on Q420 (a, b), 2Cr (c, d), 5Cr (e, f) and 9Cr (g, h) steels after corrosion for 72 h (a, c, e, g) and 360 h (b, d, f, h)

2.3 锈层XRD分析

Fig.4 XRD patterns of Q420 (a), 2Cr (b), 5Cr (c) and 9Cr (d) steels after corrosion for 360 h and removing of the outer rust layer

3 结论

(1) Q420钢在模拟的高盐度大气环境中的腐蚀速率基本保持不变,含Cr钢腐蚀速率先增大后减小,且在实验周期内耐蚀性能优于Q420钢。

(2) 含Cr钢腐蚀初期锈层不稳定,随着腐蚀过程的进行,锈层致密性和稳定性提高,能够有效阻碍腐蚀性介质的传输,提高了材料的耐蚀性能。

(3) Q420钢的锈层疏松多孔,主要组成为Fe2O3和Fe3O4,对基体不能起到良好的保护作用;含Cr钢锈层分为内外两层,外锈层组成为Fe2O3和Fe3O4,内锈层组成为α-FeOOH,Fe2O3和Fe3O4。Cr促进了内锈层中α-FeOOH的形成,提高了锈层的稳定性和致密性,材料耐蚀性能增强。

The authors have declared that no competing interests exist.

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