时效时间对2101双相不锈钢电化学腐蚀行为的影响

EFFECT OF AGING TIME ON ELECTROCHEMICAL CORROSION BEHAVIOR OF 2101 DUPLEX STAINLESS STEEL

采用电化学动电位极化曲线和动电位再活化(EPR)技术系统研究了时效处理对2101双相不锈钢(DSS 2101)腐蚀行为的影响.利用扫描电镜(SEM)观察了电化学测试之后的样品表面形貌.结果表明:随着时效时间的增加,样品耐点蚀和耐晶间腐蚀能力逐步下降,分别对应于破裂电位的下降和活化率的升高.对于固溶样品,点蚀优先发生在铁素体内部;对于时效态的样品,点蚀优先发生在氮化物附近,即二次奥氏体上.对析出动力学与电化学腐蚀行为之间的关系进行了讨论.

Duplex stainless steels （DSS） are extensively applied in many fields such as petroleum industry, petrochemistry, desalination service and pape-making industry. They are characterized by a two-phase structure, offering an attractive combination of corrosion resistance and mechanical properties. Their best general properties are obtained by keeping approximately equal volume fractions of austenite and ferrite but averting third harmful phases, such as a, y2, X, carbide and nitride, to be precipitated. These harmful phases can be formed from ferrite when DSS are welded or worked at improper high temperatures. Recently, a kind of economical DSS 2101 of typical composition Fe- 21.4Cr-l.2Ni-5.7Mn-0.23N-0.31Mo was developed and shows a wide application potential due to its higher yield strength, better pitting corrosion resistance and lower cost than traditional 304 austenite steel. However, limited research has been dedicated to studying the microstructure and mechanical properties of DSS 2101. Especially research on the nature of precipitations and their effects on mechan- ical properties in DSS 2101 was still lacking in comparison to many researches on the precipitations in DSS 2205 and DSS 2507. In the present work, it aims at investigating how the precipitations can affect the corrosion resistance of DSS 2101. Pitting corrosion resistance of samples aged at 700 ~C in 1 mol/L NaC1 solution was evaluated by potentiodynamic polarization curve test. The electrochemical poten- tiokinetic reactivation （EPR） test was also used to evaluate the degree of sensitization to intergranular corrosion. Scanning electron microscopy （SEM） and optical microscopy （OM） were used to observe the surface morphology after electrochemical tests. The results demonstrate that both the resistance to pitting （Eb） and intergranular corrosion （Re） decreases with aging time increasing. Pitting nucleates preferentially in the ferrite phase for the solution-annealed sample, while the initiation of pitting corrosion takes place around Cr2N, in the newly formed secondary austenite for the aged specimen. EPR tests conducted at room temperature are able to detect the sensitization to Ra due to Cr2N precipitation. With increasing aging time, more Cr2N particles are precipitated at phase interfaces and grain boundaries, causing a continuous decrease of resistance to intergranular corrosion.