EFFECTS OF A Cu ADDITION ON THE CORROSION RESISTANCE OF LOW-ALLOY PRE-HARDENED PLASTIC MOLD STEEL

Abstract

The influence of Cu on the corrosion performance of low-alloy Cu-bearing pre-hardened plastic mold steel was investigated and compared with non-Cu-bearing mold steel using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), salt-spray tests and electrochemical impedance spectroscopy (EIS). The results reveal that the formed rust layer is composed of α-FeOOH, β-FeOOH, γ-FeOOH, Fe3O4 and large amounts of amorphous compounds. The corrosion product in the early stages of corrosion is loose and porous but becomes denser and more tightly bound to the steel matrix in the later stages, and the corrosion rate of Cu-bearing steel decreases with the increasing corrosion time. With a further Cu addition, the free-corrosion potential of Cu-bearing steel increases and, consequently, the electrochemical impedance, the capacitive single semicircular arc on the impedance spectra and the charge transfer resistance are also significantly enhanced. Therefore, Cu effectively enhances the corrosion resistance of pre-hardened mold steel, prolonging its service life and ensuring a high quality and shape fidelity of molded plastic products.