In the last years, new approaches for the evaluation of the corrosion resistance of martensitic stainless steels were developed, which allow nearly nondestructive as well as short-term corrosion testing. This work analyzes the sensitive influence of microstructure and surface treatment on the corrosion resistance. The effect of alloy composition and microstructure, which is always present in addition to the influence of various surface treatments will be evaluated and discussed. The corrosion behavior was investigated with conventional evaluation of the pitting potential, electrochemical potentiodynamic reactivation (EPR), electrochemical noise (EN), and the "KorroPad" (KP) technique. EPR provided information about the passivation ability and the extent of chromium content reduction due to chromium carbide precipitation in the microstructure. The use of EN and KP aims to detect the influence of different surface treatment parameters on the corrosion resistance in a nearly non-destructive way. Furthermore the results shall demonstrate the functionality and convenience of the short-term corrosion test methods EN and KP in order to gain more acceptance within the scientific community. The results will allow the extraction of surface treatment effects on the corrosion behavior of the martensitic stainless steels 1.4116, 1.4034, and 1.4021.

Martensitic stainless steels are commonly used in cutlery fabrication requiring high hardness and sufficient corrosion resistance. The heat treatment process affects the mechanical and electrochemical behavior of martensitic stainless steels due to the precipitation of chromium carbides. Depending on the heat treatment the corrosion resistance of these steels can vary strongly, and improper heat treatment parameters can lead to a weak pitting corrosion resistance. The aim of this work is to identify heat treatment parameters influencing the corrosion resistance of martensitic stainless steels by using three different electrochemical testing methods. To this purpose, five different heat treatments were applied to the alloys 1.4116 and 1.4034. In addition to the determination of the critical pitting potentials and the modified double-loop electrochemical potentiodynamic reactivation tests (DL-EPR) a new KorroPad indicator test was used assessing the pitting corrosion behavior. The results showed that all methods used were in good agreement for verifying the influence of the various heat treatment parameters on the corrosion behavior and to identify the effect of heat treatment conditions on the pitting corrosion resistance.

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The present work describes the combination of electrochemical investigations by using a gel-type electrolyte with Fourier-transformed infrared spectroscopy to investigate partially extremely thin corrosion product films on titanium-zinc. The gel pad method enables the determination of corrosion relevant parameters such as the potential and the linear polarization resistance without altering the corrosion product layers, which are extremely prone to re-dissolution when freshly formed. Complementary infrared spectroscopy enables the determination of main compounds of even very thin surface layers of few tenth of nanometers with a certain lateral resolution. It was found that zinc forms mostly zinc carboxyhydroxides such as hydrozincite, under various exposure conditions. The protective properties of these hydrozincite layers depend on the structure of the corrosion product film rather than on its thickness. In mid-term exposure tests, shallow corrosion pits were found even in the absence of corrosive agents such as chloride. K E Y W O R D Scorrosion investigations, gel-type electrolytes, infrared spectroscopy, titanium-zinc | INTRODUCTIONZinc plays a prominent role in corrosion prevention. Almost half of the 13 million tons of the annual production is used as anti-corrosive layer for steel components [1] particularly under atmospheric conditions. For that reason, the corrosion behavior of zinc and the formation of reaction products has been intensively investigated over decades. The recently published critical review by Wallinder and Leygraf [2] very impressively summarizes current and future research activities. The standard potential of zinc is rather negative E 0 Zn=Zn 2þ ¼ À0:76 V SHE , being reason why zinc usually dissolves in acidic solutions (Eq. (1)) under hydrogen evolution (hydrogen corrosion):This reaction occurs spontaneously (ΔG 0 < 0) and expresses the high reactivity of zinc. However, according to Kruse [3] the hydrogen corrosion of zinc in water at low temperatures is kinetically inhibited and can be neglected. Only the oxygen corrosion under formation of hydroxides has to be regarded (Eq. (2)):

Funding informationMDZ WP e.V.; Jens Schiller at WMF Electrochemical tests, hardness measurements, and microstructure analysis are performed to study the influence of austenitizing, quenching, and tempering parameters on the corrosion resistance of the martensitic stainless steel grade X50CrMoV15 (1.4116). Different heat treatment states were studied using an adapted EPR-Test to evaluate the chromium distribution and depletion caused by the formation and dissolution of chromium rich carbides. The EPR results were correlated with pitting corrosion behavior, demonstrating the strong effect of heat treatment parameters on the susceptibility of martensitic stainless steels to corrosion phenomena. K E Y W O R D S electrochemical potentiokinetic reactivation, heat treatment, martensitic stainless steel, pitting corrosion 1338 |