022Cr25Ni7Mo4N双相不锈钢选择性腐蚀行为与两相组织的关系研究

Relationship Between Selective Corrosion Behavior and Duplex Structure of 022Cr25Ni7Mo4N Duplex Stainless Steel

采用电化学测试、热力学计算以及SEM、AES和XPS分析等方法研究了022Cr25Ni7Mo4N双相不锈钢选择性腐蚀行为与两相组织的关系。结果表明:022Cr25Ni7Mo4N双相不锈钢阳极极化曲线具有明显的"活化-钝化-过钝化"三段特征;在活化向钝化转换区间,存在两个阳极活化峰并分别对应-236～-238 mV的γ相溶解电位E_h和-287～-294 mV的α相溶解电位E_l;022Cr25Ni7Mo4N钢具有更高的E_l电位、更低的E_h电位及更小的阳极活化电位差ΔE,这与该钢较小的两相PREN差值相关;增加Cr、Mo、N含量可同时提升实验用钢α、γ两相PREN值,25.4%Cr,4.8%Mo和0.28%N (质量分数)成分条件下,两相间PREN值均可实现平衡;实验钢钝化膜中Cr主要以Cr_2O_3氧化物存在,α相处钝化膜过渡区宽度较γ相处的更窄。

The relationship between the selective corrosion behavior and the microstructure of 022Cr25Ni7Mo4N duplex stainless steel was studied by means of electrochemical test,thermodynamic calculation,SEM,AES and XPS.The results show that the anodic polarization curve of test steel has obviously three stages,activation-passivation-transpassivation.In the conversion interval of activation to passivation,there exist two anode activation peak potentials,Eh=-236^-238 mV and El=-287^-294 mV,which may corresponds to the dissolution potential ofγ-phase andα-phase respectively.022Cr25Ni7Mo4N steel has a higher El potential,a lower Eh potential and a smaller anode activation potential differenceΔE,which is related to the smaller difference of pitting resistance equivalent number(ΔPREN)betweenα-phase andγ-phase of the steel.The increase of Cr,Mo and N content can simultaneously increase the PREN value ofα-phase andγ-phase of the test steel,and it can reach the balance of PREN between the two phases for the steel composed of 25.4%Cr,4.8%Mo and 0.28%N(mass fraction).In such case,the Cr in the passive film is mainly as the chromia Cr2O3,and the transition zone width of the passivation film onα-phase is narrower than that onγ-phase.