Corrosion behavior of PH13-8Mo stainless steel after long-term exposure to semi-rural atmosphere
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摘要: 在北京半鄉村大氣環境中對未經預鈍化及硝酸預鈍化后的PH13-8Mo不銹鋼進行5 a的長周期暴曬試驗,通過表面形貌觀察、質量損失分析、表面鈍化膜及腐蝕產物膜層分析、力學性能檢測及斷口分析等方法,研究了硝酸預鈍化處理對PH13-8Mo長周期腐蝕行為的影響規律及機理。結果表明,經5 a大氣暴曬試驗,硝酸預鈍化處理減輕了PH13-8Mo不銹鋼的點蝕、降低其均勻腐蝕速率,通過降低PH13-8Mo不銹鋼鈍化膜中的氫氧化物含量、提高Cr/Fe原子比并提高大氣暴曬后表面的Kelvin電位,延遲了Cl?對鈍化膜的破壞及點蝕的形核,進而提高了表面膜層對基體的保護作用。硝酸預鈍化處理能減少在半鄉村大氣環境中PH13-8Mo不銹鋼力學性能的下降,但對試樣的斷裂方式幾乎沒有產生影響,二者均為韌性斷裂,斷口均呈現典型的“杯錐狀”。
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關鍵詞:
- PH13-8Mo不銹鋼 /
- 硝酸預鈍化處理 /
- 半鄉村大氣腐蝕 /
- 鈍化膜 /
- 力學性能
Abstract: PH13-8Mo is a precipitation-strengthened, martensitic stainless steel with ultra-high strength, and satisfactory toughness and plasticity. It is generally utilized in the fields of aviation and traditional energy because of its remarkable mechanical properties and corrosion resistance, as well as its stable performance in harsh service environments. Because of the wide applications of PH13-8Mo stainless steel and the complex corrosive environments it faces, its corrosion resistance is of great significance for deciding the lifetime and safety of aircrafts and ships. However, limited by factors, including a long outdoor exposure test cycle and a large professional experimental site required, only a few reports exist on the atmospheric corrosion behavior and mechanism of PH13-8Mo stainless steel, especially the influence of chemical pre-passivation on the steel still remains relatively uninvestigated. Therefore, the outdoor exposure tests of two samples of PH13-8Mo stainless steel, with and without nitric-acid-passivated film, respectively, were performed in a semi-rural atmospheric environment in Beijing for five years. The effect of the pre-passivation treatment on the corrosion behavior and mechanism of PH13-8Mo stainless steel was investigated by observing the surface morphology, using the mass loss method, analyzing the passivated film and corrosion products, testing the mechanical properties, and conducting fracture analyses. The results show that the pre-passivation treatment with nitric acid reduces the pitting corrosion and decreases the corrosion rate. The pre-passivation treatment with nitric acid delays the destruction of Cl? on the passivated film and also delays the nucleation of the pitting by increasing the hydroxide content and the atomic ratio of Cr/Fe of the passivated film, and it increases the surface Kelvin potential as well, further enhancing the protectiveness of the surface film. Additionally, the pre-passivation treatment with nitric acid reduces the loss in the mechanical properties after long-term exposure to the semi-rural atmospheric environment, although it has little effect on the fracture mode, and both the steel samples exhibit the typical morphologies of a ductile fracture. -
圖 3 北京大氣暴曬5 a后PH13-8Mo試樣形貌。(a)未經鈍化試樣宏觀形貌;(b)預鈍化后試樣宏觀形貌;(c)未經鈍化試樣除銹前微觀形貌;(d)預鈍化后試樣除銹前微觀形貌;(e)未經鈍化試樣除銹后微觀形貌;(f)預鈍化后試樣除前后微觀形貌
Figure 3. Morphologies of the samples after five-year exposure in Beijing: (a) macro morphologies of bare samples; (b) macro morphologies of pre-passivated samples; (c) micro morphologies of bare samples before rust removal; (d) micro morphologies of pre-passivated samples before rust removal; (e) micro morphologies of bare pre-passivated samples after rust removal; (f) micro morphologies of pre-passivated samples after rust removal
圖 7 北京大氣暴曬5 a后PH13-8Mo不銹鋼拉伸試樣形貌。未經鈍化試樣(a)和預鈍化試樣(b)宏觀形貌;未經鈍化試樣(c)和預鈍化試樣(d)斷口微觀形貌
Figure 7. Morphologies of the tensile specimens of PH13-8Mo stainless steels after five-year exposure in Beijing: macro morphologies of bare sample (a) and pre-passivated sample (b); fracture morphologies of bare sample (c) and pre-passivated sample (d)
表 1 PH13-8Mo不銹鋼的化學成分(質量分數)
Table 1. Composition of experimental steel
% C Si Mn P S Cr Ni Al Mo Fe 0.055 0.065 0.046 0.023 0.02 12.42 8.14 1.14 2.40 Balance 表 2 試驗期間北京試驗站環境數據
Table 2. Experimental conditions of the Beijing experiment station
Experiment stations Climate Weather factors(annual average) Corrosion concentration/(μg·cm?2·d?1) Beijing 39.98°N, 116.26°E Altitude:73 m Warm temperate and semi-humid,semi-rural atmospheric Temperature:13.8 ℃ Rainfall: 388.8 mm Relative humidity: 44.6% H2S:0.575 Sea-salt particles:0.313 Sulfation rate:2.869 表 3 PH13-8Mo試樣力學性能數據
Table 3. Mechanical properties of PH13-8Mo stainless steels
Samples σ0.2 /MPa σb /MPa δ /% Bare sample 1308 1343 15.3 Pre-passivation sample 1331 1365 15.6 Original sample 1339 1380 16.1 表 4 PH13-8Mo不銹鋼暴曬后膜層主要化學成分的結合能
Table 4. Binding energies of the primary compounds of the PH13-8Mo stainless steel
Element Peak Species: binding energy Cr 2p3/2 Cr(met): 574.7 eV; Cr2O3:576.8 eV; Cr(OH)3:
577.4 eV; CrO3:578.9 eVFe 2p3/2 Fe(met): 706.74 eV; FeOOH:711.8 eV; Fe3O4:
708.1 eV; Fe2O3:710.4 eV; FeO:709.6 eVO 1s O2?: 530.2 eV; OH?:531.5 eV; H2O: 532.8 eV 259luxu-164 -
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