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目的：探究分别在40℃和60℃下,拉应力与2205双相钢耐点蚀性能的关系。方法分析2205双相不锈钢在施加0、140、540 MPa三种拉应力的条件下,于临界点蚀温度以下(40℃)和临界点蚀温度附近(60℃)的3.5%NaCl溶液中的动电位极化行为,并对比了不同拉应力对2205双相钢阻抗特性的影响。结果动电位极化曲线表明,140 MPa下点蚀电位稳定,40、60℃下击破电位分别为0.7、0.8 V；540 MPa拉应力使双相钢点蚀电位从无应力时的0.9 V下降至0.3 V。阻抗分析表明,40℃时所有样品均为单一阻抗特征,且阻抗值较大,应力会降低阻抗值。在60℃、开路电位条件下,0、140 MPa拉应力时具有较高阻抗,540 MPa拉应力时为具有点蚀萌生的阻抗弧；在60℃、600 mV偏压条件下,0、540 MPa拉应力时呈现点蚀阻抗特征,而140 MPa时阻抗仍较高。阻抗谱等效电路拟合结果结合不锈钢表面微观形貌表明,在40℃溶液中,OCP及600 mV偏压下试样表面均没有发生点蚀,应力对钝化膜电阻Rp 没有明显影响,阻抗值为30000Ω·cm2左右。温度升高至60℃后,钝化膜阻值明显降低；开路电位、540 MPa应力条件下不锈钢发生点蚀,阻抗值由0 MPa下的20000Ω·cm2左右降到10000Ω·cm2左右；在600 mV偏压下,0、540 MPa拉应力时均发生点蚀,而140 MPa时均未发现点蚀。结论在40℃和60℃,140 MPa拉应力可以抑制2205双相钢的点蚀,540 MPa拉应力则加速点蚀的发生。

ABSTRACT:Objective To study the effects of tensile stress on pitting-resistance of 2205 duplex stainless steel at 40 ℃ and 60℃. Methods The characteristics of potentiodynamic polarization was investigated under different elastic tensile stress of 0 MPa, 140 MPa and 540 MPa in 3. 5% NaCl solution below the critical pitting temperature of 40℃ and around the temperature of 60℃. The effect of different tensile stress on the impedance characteristics of 2205 duplex stainless steel was also analyzed. Results The potentiodynamic polarization curves showed a relatively stable pitting potential under condition of 140 MPa, which was about 0. 7 V and 0. 8 V at 40℃ and 60℃, respectively. However, applying tensile stress of 540 MPa significantly decreased the pitting poten-tial from 1. 0 V to 0. 3 V. The electrochemical impedance spectra (EIS) exhibited single impedance arc with high value of electric resistance, and the resistance was decreased by applying stress. As temperature increased up to 60℃, high value of impedance re-sistance was achieved under stress of 0 and 140 MPa, while a pitting initiation characteristics was observed for the EIS under 540 MPa at OCP. At bias polarization of 600 mV, the pitting arcs were observed under 0 MPa and 540 MPa, but the resistance under 140 MPa was still high. The fitting results by using equilibrium circuit plots combined with surface morphologies showed that there was no pitting occurring at 40 ℃, the resistance of the passive film Rp was around 30 000 Ω·cm2 which was not significantly af-fected by applying tensile stresses. At the temperature of 60 ℃, the resistance of passive film decreased significantly. Under the condition of OCP 540 MPa, pitting corrosion occurred, the impedance values decreased from about 20 000Ω·cm2 to about 10 000Ω·cm2 . At bias polarization of 600 mV, pitting occurred under both 0 MPa and 540 MPa, while there was no pitting under 140 MPa at 60 ℃. Conclusion At 40 ℃ and 60 ℃, the pitting of 2205 duplex steel could be inhibited under the stress of 140 MPa while the application of 540 MPa accelerated the occurrence of pitting.