固溶温度对S32760双相不锈钢组织与耐点蚀性能的影响EFFECT OF SOLUTION TEMPERATURE ON MICROSTRUCTURE
AND PITTING CORROSION RESISTANCE OF S32760 DUPLEX STAINLESS STEEL

利用 OM, EPMA, SEM, EDS, TEM 等研究了固溶温度对 S32760 双相不锈钢热轧板显微组织的影响及合金元素的分布特征, 并通过电化学工作站测定了材料的耐点蚀性能. 结果表明, S32760 双相不锈钢在 1080 ℃以上高温固溶过程中, N 元素从 γ 相扩散转移至 δ 相中. 若固溶后缓慢冷却, 则 N 原子又重新迁移回 γ 相中; 如果固溶后水冷, 则 N 原子来不及扩散, 于 δ 相中原位弥散析出 Cr2N 颗粒. Cr2N 颗粒的数量由淬火前的固溶温度决定, 温度越高数量越多. 当固溶温度从 1100 ℃升至 1300 ℃时, δ 相中 N 的固溶度快速上升, 其显微硬度由 281 HV 提高至 345 HV; 而 γ 相由于相比例降低也使得 N 的浓度间接上升, 显微硬度由 290 HV 升至 314 HV. 同时, 由于实验钢中含有 W, S32760 双相不锈钢热轧板在 1040 ℃以下热处理有σ 相析出, 因此其固溶水冷温度区间较窄, 最佳固溶温度为 1060 ℃. 此温度保温 60 min 后水冷, 试样中无析出物, Brinell 硬度为 249 HBW, 点蚀电位为 1068 mV, 维钝电流密度为 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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