The properties of a ncw, very highly alloyed stainless steel, Avesta 654 SMO, are compared with those of other stainless steels and nickel-base alloys. The new steel has a very high strength but still possesses a high elongation. The corrosion properties have been investigated in accelerated laboratory tests and in environments representing the expected main application areas, sea water, pulp bleaching and flue gas cleaning.The tests clearly show that the new steel has appreciably better corrosion resistance than the superduplex and superaustenitic 6 Mo steels and that the resistance in many cases matches that of the best nickel-base alloys.Die Eigenschaften eines neuen sehr hochlegierten nichtrostenden Stahls (AVESTA 654 SMO) werden rnit denen anderer nichtrostender Stahle sowie von Nickellegierungen verglichcn. Der neue Stahl hat trotz seiner hohen Festigkeit eine hohe Dehnung. Die Korrosionseigenschaften wurden in bcschleunigten Laborversuchen sowie in Medien untersucht, die fur die erwarteten hauptsachlichen Anwendungen reprasentativ sind (Meerwasser, Zellstoffbleiche und Rauchgasreinigung). Die Ergebnisse der Versuche zeigen deutlich, daB der neue Stahl den Superduplexstihlen und den superaustenitischen Stahlen mit 6% Molybdan hinsichtlich Korrosionsbestandigkeit deutlich iiberlegen und darin vielfach den besten Nickellegierungen gleichwertig ist.
The effect of chlorination on the corrosion resistance of different stainless steels in North Sea water has been studied, the sea‐water exposures being performed at two Norwegian seawater laboratories. In one laboratory test specimens, simulating various components used in a seawater cooling system, were immersed in the water. In the other laboratory a pipe system containing real components was studied. Seawater temperature, chlorine concentration and chlorination procedure have been varied at both laboratories. The steels investigated include highly alloyed grades like UNS S31254 (AVESTA 254 SMO), UNS S44635 (Avesta Monit) and UNS NO8028 (Sandvik Sanicro 28). The investigation shows that continuously chlorinated seawater is considerably more aggressive than unchlorinated or intermittently chlorinated seawater and that high temperature increases the risks of localized corrosion at the same chlorine concentration. The highest alloyed steel grades were very resistant to crevice corrosion even in continuously chlorinated water but certain kinds of metal‐metal crevices have to be avoided. When welded, duplex UNS S31803 was sensitive to pitting corrosion in chlorinated water. Contrary to crevice corrosion, the risk for galvanic corrosion decreases considerably if the seawater is chlorinated.
The first generation of superaustenitic 6Mo steels like 254 SMO@ has been further developed into a new steel -654 SMO@ -containing very high amounts of those alloying elements most beneficial for the resistance to localized corrosion. 654 SMO is compared with other stainless steels and nickel-base alloys in tests performed in various kinds of seawater. The new steel is much superior to the 6Mo steel under all conditions investigated and compares favourably with Alloy C-276 in most tests. The most corrosive condition among those investigated represents a seawater system where aerobic and anaerobic areas exist simultaneously.Die erste Generation der superaustenitischen 6Mo-Stahle, wie 254 SMO, ist zu einem neuen Stahl -654 SMO@ -weiterentwikkelt worden, der sehr hohe Zusatze von Legierungselemente insbesondere mit verbesserndem EinfluB auf die Bestandigkeit von Lokalkorrosion enthalt. 654 SMO wird anhand von Priifungen in verschiedenen Arten von Seewasser anderen nichtrostenden Stahlen und Nickelbasis-Legierungen vergleichend gegenubergestellt. Der neue Stahl ist dem 6Mo-Stahl unter allen gepriiften Bedingungen weit uberlegen und kann sich auch in den meisten Priifungen erfolgreich mit Alloy C-276 vergleichen. Die hochsten korrosiven Priifbedingungen lagen in einem Seewassersystem mit gleichzeitig belufteten und unbeliifteten Zonen vor.
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