EFFECTS OF GRAIN BOUNDARY CHARACTER ON INTERGRANULAR STRESS CORROSION CRACKING INITIATION IN 316 STAINLESS STEEL
Zilong ZHANG,Shuang XIA(),Wei CAO,Hui LI,Bangxin ZHOU,Qin BAI
School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
Cite this article:
Zilong ZHANG, Shuang XIA, Wei CAO, Hui LI, Bangxin ZHOU, Qin BAI. EFFECTS OF GRAIN BOUNDARY CHARACTER ON INTERGRANULAR STRESS CORROSION CRACKING INITIATION IN 316 STAINLESS STEEL. Acta Metall Sin, 2016, 52(3): 313-319.
316 stainless steel (316SS) is widely used due to a combination of good mechanical properties and excellent corrosion resistance. However, the intergranular stress corrosion cracking (IGSCC) is a serious problem for 316SS exposed to aggressive environments, which could result in unexpected failures and lead to huge losses. The grain boundary structure and local stress applied on the grain boundary are proved to have significant influence on the initiation of the IGSCC. In this work, thermal-mechanical processing was applied to the 316SS to yield a large-grained sample. The sample plates with a single-grained thickness were subjected to three-points bending SCC tests in an acidified boiling 25%NaCl solution. The result shows that the random grain boundaries (GBs) have the highest propensity to IGSCC initiation, while the Σ3 GBs shows very low tendency to IGSCC initiation. The absolute values of Schmid factor mismatch (Δm) between the grains on both sides of the GBs were analyzed for a large number of GBs. The distribution of the Δm for the Σ3 GBs is obviously different from that of the random GBs. The Δm has significant influence on the IGSCC susceptibility in the range of 0<Δm<0.1. The larger value of the Δm, the higher propensity for the IGSCC initiation at the GBs, for both the random GBs and the Σ3 GBs.
Fig.1 Schematic of specimen for stress corrosion cracking (SCC) test (a) and three-point bend test set-up for specimens (b) (unit: mm)
Fig.2 OM images of surface (a) and cross-section (b) of 316 stainless steel (316SS) after aging treatment and orientation imaging microscopy (OIM) image of different types of grain boundaries (c)
Fig.3 Histogram of grain boundary character distribution (GBCD) of 316SS
Fig.4 OM images of 316SS after SCC test for 1.5 h (a), 5 h (b) and 13 h (c)
Fig.5 SEM (a) and EBSD (b) images of 316SS in crack initiation area after SCC test for 13 h (Inset in Fig.5a shows the enlarged view of the rectangle area)
Fig.6 Number (a) and fraction (b) of cracked grain boundaries of different types of grain boundaries in 316SS after SCC test for different times
Fig.7 Dependence of number of random (a) and Σ3 (b) grain boundaries on the absolute Schmid factor mismatch between two sides of grain boundary (Δm)
Fig8 Dependence of fraction of cracked random grain boundaries on Dm categories in 316SS after SCC test for different times (Dm categories: L (0.01≤Dm≤0.03), M (0.04≤Dm≤0.06), H (0.07≤Dm≤0.09))
Fig 9 Dependence of fraction of cracked low SCSL grain boundaries on the Dm categories in 316SS after SCC test for different times
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