固溶溫度對S32760雙相不銹鋼組織與耐點蝕性能的影響EFFECT OF SOLUTION TEMPERATURE ON MICROSTRUCTURE
AND PITTING CORROSION RESISTANCE OF S32760 DUPLEX STAINLESS STEEL

利用 OM, EPMA, SEM, EDS, TEM 等研究了固溶溫度對 S32760 雙相不銹鋼熱軋板顯微組織的影響及合金元素的分布特征, 并通過電化學工作站測定了材料的耐點蝕性能. 結果表明, S32760 雙相不銹鋼在 1080 ℃以上高溫固溶過程中, N 元素從 γ 相擴散轉移至 δ 相中. 若固溶后緩慢冷卻, 則 N 原子又重新遷移回 γ 相中; 如果固溶后水冷, 則 N 原子來不及擴散, 于 δ 相中原位彌散析出 Cr2N 顆粒. Cr2N 顆粒的數量由淬火前的固溶溫度決定, 溫度越高數量越多. 當固溶溫度從 1100 ℃升至 1300 ℃時, δ 相中 N 的固溶度快速上升, 其顯微硬度由 281 HV 提高至 345 HV; 而 γ 相由于相比例降低也使得 N 的濃度間接上升, 顯微硬度由 290 HV 升至 314 HV. 同時, 由于實驗鋼中含有 W, S32760 雙相不銹鋼熱軋板在 1040 ℃以下熱處理有σ 相析出, 因此其固溶水冷溫度區間較窄, 最佳固溶溫度為 1060 ℃. 此溫度保溫 60 min 后水冷, 試樣中無析出物, Brinell 硬度為 249 HBW, 點蝕電位為 1068 mV, 維鈍電流密度為 1.48×10-4 A/cm2.
In order to obtain the optimal corrosion resistance, the characteristics of microstructure and alloy elements distribution of S32760 duplex stainless steel were studied after solid solution treatment at various temperatures from 1000 ℃ to 1300 ℃ by means of OM, EPMA, SEM, EDS and TEM. In addition, the pitting corrosion resistance was measured by the electrochemical workstation. The results show that the N atoms diffused into δ phase from γ phase during solution treatment when the temperature was higher than 1080 ℃. N atoms migrated back into γ phase when the subsequent cooling was slow enough. However, Cr2N phase in situ precipitated during quenching because there was not enough time for the N atoms to diffuse back into γ phase. Cr2N particles increased with the solution temperature increasing. Furthermore, σ phase precipitated when the tested sheet was heat treated at or below 1040 ℃ due to the high content of N. Thus it is obvious that the solution temperature range of the S32750 duplex stainless steel is quite narrow, which is between 1040 ℃ and 1080 ℃, and it is confirmed that the optimal temperature is 1060 ℃. After treated at 1060 ℃ for 60 min, the Brinell hardness of S32760 steel is 249 HBW, pitting potential is up to 1068 mV and the passive current density is as low as 1.48×10-4A/cm2.
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