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Nickel‐free high‐nitrogen‐alloyed stainless steels like the P2000 (X13CrMnMoN18‐14‐3) were developed to enhance the strength and corrosion resistance of austenitic stainless steels like 304 and 316 while keeping the typical high ductility. The mechanical and corrosive properties of P2000 were investigated and compared with 304 and 316 to highlight the application opportunities of this new alloy. The microstructure of the solution‐annealed condition was characterised by electron backscatter diffraction and the mechanical properties were studied by uniaxial tensile tests, Charpy impact tests and hardness measurements. The passivation behaviour was analysed using the electrochemical potentiodynamic reactivation, whereas the pitting corrosion resistance was compared by pitting potentials and pitting temperatures. However, secondary thermal influences or suboptimal heat treatment can impair the corrosion resistance due to the precipitation of secondary phases and the resulting sensitisation. Thermodynamic calculations and artificial ageing treatment in the range of 500–900°C for up to 100 h were used to determine critical time–temperature parameters for sensitisation. The microstructure of the various aged states was evaluated by scanning electron microscopy and compared with the degrading corrosion resistance characterised by the KorroPad method.
Die Qualität von Schneidwaren aus martensitisch nichtrostenden Stählen (MNS) hängt neben ihrer härtebedingten Schneidleistung wesentlich von ihrer Korrosionsbeständigkeit ab, die dauerhaft das hochwertige optische Erscheinungsbild gewährleisten soll. Zur Prüfung der Korrosionsbeständigkeit hat sich bei Schneidwaren aus MNS die Anwendung des Wechseltauchversuchs etabliert, dessen Ausweitung aufwendig und dessen Ergebnisse oftmals fragwürdig sind. In den letzten Jahren wurden daher neue elektrochemische Methoden entwickelt, um das Korrosionsverhalten von MNS objektiver zu bewerten. Diese neuen Untersuchungsmethoden ermöglichen eine genauere Erfassung der teilweise stark schwankenden Korrosionsbeständigkeit von MNS und bilden damit die Grundlage zur Aufklärung der Ursachen dieser Schwankungen. Im Rahmen des IGF-Vorhabens 16636 BG wurden dazu das elektrochemische Rauschen (ECR), das KorroPad und die elektrochemisch potentiodynamische Reaktivierung (EPR) eingesetzt, um die werkstoffseitigen Einflüsse der Mikrostruktur und den Einfluss der Oberflächenbearbeitung auf die Korrosionsbeständigkeit zu untersuchen. Es wurden dazu an drei weit verbreiteten MNS (1.4116, 1.4034 und 1.4021) je acht verschiedene Oberflächenzustände hergestellt und das Korrosionsverhalten untersucht. Um die dabei aufgetretenen Unterschiede im Lochkorrosionsverhalten zwischen den drei Werkstoffen zu erklären, wurde der EPR-Test eingesetzt, der lokale ChromVerarmung im Gefüge als werkstoffbedingte Ursache von Lochkorrosionsanfälligkeit nachweist. Mit der Kombination der Ergebnisse aus EPR, ECR und KorroPad war es möglich, die unterschiedliche Lochkorrosionsanfälligkeit direkt der unterschiedlich stark ausgeprägten Chromverarmung der drei MNS zuzuordnen. Der Einfluss der Chromverarmung auf die Lochkorrosionsanfälligkeit ist dabei deutlich größer als der Effekt der Oberflächenbearbeitung, der nur bei gering ausgeprägter Chromverarmung ersichtlich ist. Damit wurde gezeigt, dass nur bei Betrachtung aller Einflussgrößen sichere Aussagen zur Korrosionsbeständigkeit und zu den Ursachen der Lochkorrosionsanfälligkeit von MNS möglich sind.
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.
As bio-absorbable implant material the magnesium alloy Mg-1Ca is able to degrade in-vivo. The mechanical properties of this alloy are similar to those of human bone; both Mg and Ca are essential elements in human body. The main problem is the high corrosion rate of this alloy. Two coating systems based on plasma-chemical oxidation and an organic dip coating are applied onto MgCa1.0 magnesium alloy in order to slow down the corrosion rate. The corrosion behaviour of the coated alloys was investigated with electrochemical noise measurements. The influence of hydrogen evolution and increasing pH-value on the cytotoxicity was examined. The results of these investigations suggest that a combination of both coating systems leads to promising degradation properties.
Samples of the austenitic stainless steel grade X5CrNi18‐10 (1.4301, AISI 304) were ground industrially with various grinding parameters to study their influence on corrosion resistance. The ability of the mechanically ground surfaces to form a stable passive layer was evaluated by KorroPad test and a modified electrochemical potentiodynamic reactivation test based on a single loop (EPR‐SL). Furthermore, the surfaces were characterized by surface analytical methods. The main influence was determined regarding abrasive belt type. Surfaces mechanically ground with granulate abrasive belts constantly had a lower corrosion resistance than surfaces ground with single‐coated grain. The granulate abrasive belts generated more sensitized surface areas and left formations of welded sample material on the mechanically ground surfaces. A post‐treatment with a nonwoven abrasive proved to be an effective finishing process by which the surface defects and sensitized material got removed and the surfaces regained the expected corrosion resistance.
In the last years, new approaches for the evaluation of the corrosion resistance of stainless steels were developed which allow short term corrosion testing with increased information content. This work analyses the extensive influence of heat treatment on microstructure and the resulting corrosion resistance of the martensitic stainless steels 1.4034 and 1.4021 with advanced methods. Different heat treatments at various austenitization temperatures up to 1100°C and the effect of different cooling rates were evaluated; the last has not yet been studied in literature at all. The resulting corrosion behaviour in relation to the different carbon content in the two used alloys and the applied heat treatment will be presented and discussed. The applied methods of investigation were conventional evaluation of the critical pitting corrosion potential (PP), modified electrochemical potentiodynamic reactivation (mEPR) and the "KorroPad" (KP) technique. The performance of modified EPR and its interpretation were optimized to provide additional information about the general passivation ability and the extent of chromium depletion as result of applied heat treatment. The aim using PP and KP was the correlation between the Parameters of the mEPR with the changes in the pitting corrosion resistance. Furthermore the results will demonstrate the functionality and usability of the short term corrosion test methods mEPR and KP in order to increase their acceptance within the scientific community. The results indicate a surprisingly large influence of both austenitization temperature and cooling rate on the corrosion resistance within all three used test methods, which can explain the different corrosion behaviour of martensitic stainless steels in earlier investigations.
In the last years, new approaches for the evaluation of the corrosion resistance of martensitic stainless steels were developed, which allow nearly non-destructive 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.
Die Magnesiumlegierung Mg-Cal besitzt als potentielles bioabsorbierbares Implantatmaterial die Möglichkeit, vollständig vom menschlichen Körper absorbiert zu werden. Die mechanischen Kennwerte dieser Legierung liegen im Bereich des menschlichen Knochens und beide Legierungselemente (Mg, Ca) sind essentielle Spurenelemente im menschlichen Organismus.
Der limitierende Faktor für den Einsatz ist die hohe Degradationsrate dieser Legierung. Um die Degradationsgeschwindigkeit zu verringern, wurden zwei Beschichtungssysteme auf Grundlage der Plasmachemischen Oxidation (PCO) und organischer Beschichtung erzeugt und untersucht. Das Korrosionsverhalten dieser Schichtsysteme wurde dabei mit dem Elektrochemischen Rauschen analysiert. Zusätzlich wurde der Einfluss von Wasserstoffentwicklung und eines ansteigenden pHWert auf die Zelltoxizität untersucht. Die Ergebnisse zeigen, dass eine Kombination von beiden Schichtsystemen zu einem viel versprechenden Degradationsverhalten führt.