蠕墨铸铁中性盐雾腐蚀行为及机理研究

Corrosion Behavior and Mechanism of Vermicular Graphite Cast Iron in Neutral Salt Spray

目的揭示蠕墨铸铁的大气腐蚀行为,阐明其腐蚀规律及腐蚀机理。方法采用室内加速中性盐雾腐蚀实验,并用失重法、SEM\EDS、XRD、电化学的方法来表征实验现象。结果蠕墨铸铁在中性盐雾环境中锈层截面具有明显的分层现象,前期腐蚀速率为0.53 mg/(cm^2·h),后期腐蚀速率在波动中总体趋于稳定,为0.36 mg/(cm^2·h)。蠕墨铸铁带锈试样的自腐蚀电位(Ecorr)在-680^-600 mV之间先减小后增大,极化电阻(Rp)变化趋势与自腐蚀电位(Ecorr)一致,自腐蚀电流(Icorr)大小在整个腐蚀周期内具有明显的波动。蠕墨铸铁在中性盐雾环境中的腐蚀产物为Fe(OH)3、Fe2O3、FeOOH及少量Fe3O4和金属碳化物Fe2C。结论蠕墨铸铁在中性盐雾环境中腐蚀84 h后发展为全面腐蚀,形貌呈沟壑状,腐蚀产物微观形貌呈团簇状和片层状。腐蚀早期,基体表面发生电化学腐蚀形成一层氧化膜,腐蚀介质沿石墨侵蚀基体从而产生内应力,导致外部锈层断裂,同时蠕虫状石墨处腐蚀产物呈疏松团簇状,二者共同构成介质传质通道,使腐蚀更容易发展。

The work aims to reveal the atmospheric corrosion behavior of vermicular graphite cast iron(VGCI)and clarify the corrosion law and corrosion mechanism.Accelerated salt spray corrosion experiments were carried out in laboratory,and the results were characterized by weight loss,SEM/EDS,XRD and electrochemical methods.The cross section of VGCI had obvious stratification in neutral salt spray.The corrosion rate was 0.53 mg/(cm^2×h)in the early stage,and then fluctuated in the later stage,but the overall stability tended to be 0.36 mg/(cm^2×h).The corrosion potential(Ecorr)of the vermicular graphite cast iron rust sample decreased first and then increased from-680 mV to-600 mV,and the change trend of the polarization resistance(Rp)was consistent with the corrosion potential(Ecorr).The self-corrosion current(Icorr)had obvious fluctuations throughout the corrosion cycle and the corrosion products of VGCI in neutral salt spray were:Fe(OH)3,Fe2O3,FeOOH and a small amount of Fe3O4 as well as metal carbide Fe2C.VGCI can be developed into comprehensive corrosion after 84 h in neutral salt spray environment,with gully appearance and the microscopic appearance of corrosion products is shown in clusters and lamella.In the early stage of corrosion,an oxide film is formed on the surface of the matrix due to electrochemical corrosion,and the corrosive medium corrodes the matrix along the graphite to generate internal stress,resulting in the fracture of the outer rust layer.At the same time,the corrosion products on the worm-like graphite are in loose clusters.The two together forms the medium mass transfer channel,making the corrosion easier to develop.