ＳＳＲＴ条件下におけるＭＩＭ法により作製されたＳＵＳ３０４ステンレス鋼の腐食特性

Abstract

In this study, the corrosion behavior of MIM (Metal Injection Molding) specimen has been investigated by SSRT (Slow Strain Rate Tensile) test and EIS (Electrochemical Impedance Spectroscopy) method in comparison with I/M (Ingot Metallurgy) specimen. In the SSRT test, the aqueous solution composed of 2.5 kmol·m−3 H2SO4 and 0.20 kmol·m−3 NaCl (hereafter shortened as SCC solution) in which SCC occurs was used. In addition to this solution, the aqueous solution of 2.5 kmol·m−3 H2SO4 and 3.0 kmol·m−3 NaCl (hereafter shortened as general corrosion solution) in which general corrosion occurs was used in the EIS test.Cdl (Electric Double Layer Capacitance) of I/M specimen has increased abruptly at 7.2 ks during holding in the SCC solution under applied stress, while it has increased gradually without applied stress. On the other hand, the Cdl of MIM specimen has increased gradually increased irrespective of with or without applied stress for MIM specimen. The remarkable Rct difference was observed in two cases with or without applied stress in the SCC solution for both I/M and MIM specimen while the slight Rct difference was observed in the general corrosion solution. The fracture surface appearance by SEM showed that the typical transgranular SCC occurred on I/M specimen while the intergranular SCC along grain boundaries occurred on MIM specimen. It was also confirmed that the more significant HE-SCC (Hydrogen Embrittlement) and the weaker APC-SCC (Active Path Corrosion) were observed on the MIM specimen compared with the I/M specimen.