Zhang Zhiying, Yue Shumin, Gong Yanlong, Yang Xiao, Chen Tao, Zhang Qinyi
The corrosion and electrochemical properties of several tool steels, including 4V, S35VN, 14C28N and BD1N, in phosphate buffer saline(PBS) solution were investigated by potentiodynamic polarization tests, electrochemical impedance spectroscopy(EIS), optical microscopy, scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS), and compared with austenitic stainless steels 304 and 316L. The potentiodynamic polarization results illustrate that passivation occurs in all specimens, indicating desirable corrosion resistance in PBS solution. EIS results reveal that the electrode process is controlled by electrochemical reaction steps. Spontaneous corrosion potential Ecorr of 4V steel is the lowest, which is -0.766 VSCE, while corrosion current density Jcorr is the highest, which is 6.61×10-5 A/cm2, and capacitance arc as well as the sum value of passivation film resistance Rf and charge transfer resistance Rct are the smallest, where the latter is 1.00×103 Ω·cm2, leading to the worst corrosion resistance. The sequence of corrosion resistance is presented as follows: 4V< S35VN< 14C28N< BD1N< 304< 316 L. Localized corrosion occurs in all the tool steels in PBS solution. Cr content in 4V steel is lower, resulting in the poor corrosion resistance, while that in S35VN, 14C28N and BD1N are high, contributing to the stable passivation films and desirable corrosion resistance. The high Cr and Ni content in 304 and 316L austenitic stainless steels is helpful to the stable passivation films, giving rise to excellent corrosion resistance.
