Dependence of corrosion resistance on grain boundary characteristics in a high nitrogen CrMn austenitic stainless steel

doi:10.1016/j.jmst.2017.09.016

Abstract

Abstract:

Processing schedules for grain boundary engineering involving different types of cold deformation (tension, compression, and rolling) and annealing were designed and carried out for 18Mn18Cr0.6N high nitrogen austenitic stainless steel. The grain boundary characteristic distribution was obtained and characterized by electron backscatter diffraction (EBSD) analysis. The corrosion resistance of the specimens with different grain boundary characteristic distribution was examined by using potentiodynamic polarization test. The corrosion behavior of different types of boundaries after sensitization was also studied. The fraction of low-Σ boundaries decreased with increasing strain, and it was insensitive to the type of cold deformation when the engineering strain was lower than 20%. At the strain of 30%, the largest and smallest fractions of low-Σ boundaries were achieved in cold-tensioned and rolled specimens, respectively. The fraction of low-Σ boundaries increased exponentially with the increase of grain size. The proportion of low-angle grain boundaries increased with decreasing grain size. Increasing the fraction of low-Σ boundaries could improve the pitting corrosion resistance for the steels with the same grain size. After sensitization, the relative corrosion resistances of low-angle grain boundaries, Σ3 boundaries, and Σ9 boundaries were 100%, 95%, and 25%, respectively, while Σ27 boundaries, other low-Σ boundaries and random high-angle grain boundaries had no resistance to corrosion.

Key words: High nitrogen stainless steel, Grain boundary engineering, Coincidence site lattice, Corrosion resistance

Qi Jianjun, Huang Boyuan, Wang Zhenhua, Ding Hui, Xi Junliang, Fu Wantang. Dependence of corrosion resistance on grain boundary characteristics in a high nitrogen CrMn austenitic stainless steel[J]. J. Mater. Sci. Technol., 2017, 33(12): 1621-1628.

Figures/Tables 13

Table 1 Chemical composition of 18Mn18Cr0.6N austenitic stainless steel (in wt% pct).

C	Cr	Mn	N	Si	Ni	P	S	Fe
0.084	18.06	17.9	0.62	0.46	0.2	0.009	0.002	Bal.

Fig. 1. Microstructures of etched stainless steel after sensitization: (a) and (b) show the microstructures at two different regions.

Fig. 2. OIM maps of the steel tensile deformed at different strains after annealing at 1000 °C for 24 h: (a) 5%; (b) 10%; (c) 20%; and (d) 30%. D denotes average grain size.

Fig. 3. OIM maps of the steel compressed at different strains after annealing at 1000 °C for 24 h: (a) 5%; (b) 10%; (c) 20%; and (d) 30%.

Fig. 4. OIM maps of the steel rolling deformed at different strains after annealing at 1000 °C for 24 h: (a) 5%; (b) 10%; (c) 20%; and (d) 30%.

Fig. 5. Fraction of low-Σ boundaries under different deformation conditions.

Fig. 6. Relationships among grain size and the fraction of low-Σ boundaries (a) and the LAGBs (b).

Fig. 7. Potentiodynamic polarization curves of the steel with different GBCD.

Fig. 8. Intergranular corrosion in the sensitized specimen (a) and the corresponding band contrast map (Region 1) (b).

Fig. 9. Intergranular corrosion in the sensitized specimen (a) and the corresponding band contrast map (Region 2) (b).

Fig. 10. Intergranular corrosion in the sensitized specimen (a) and the corresponding band contrast map (Region 3) (b).

Fig. 11. Intergranular corrosion in the sensitized specimen (a) and corresponding band contrast map (Region 4) (b).

Table 2 Relative corrosion resistance of different boundaries calculated from the corroded length fraction.

Boundary	Relative corrosion resistance
LAGBs	100%
Σ3	95%
Σ9	25%
Σ27	0%
Other low-Σ	0%
Random	0%

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