研究了晶界结构特征及晶界两侧晶粒的变形难易程度(Schmid因子)对316不锈钢(316SS)不同晶界萌生应力腐蚀开裂(SCC)裂纹的影响. 通过形变及热处理工艺获得晶粒尺寸较大的样品, 制作成薄样品, 使样品厚度相当于一个晶粒的尺寸. 采用三点弯曲加载方式, 在沸腾的酸化NaCl溶液中进行SCC实验来研究316SS不同晶界萌生SCC裂纹的倾向性. 结果表明, 沿晶型的SCC裂纹在随机晶界处萌生的倾向性最高, 而在Σ3晶界处的SCC裂纹萌生倾向性很低. 分别统计了大量随机晶界和Σ3晶界两侧晶粒的Schmid因子及其差值的绝对值(Δm), 结果表明, 随机晶界数量随Δm值的变化规律不明显, Σ3晶界数量随Δm值增大明显下降; 在0<Δm<0.1范围内, 随机晶界和Σ3晶界萌生SCC裂纹的倾向性都随着Δm的增加而增加.
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.
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