STUDIO DELL'EFFETTO DELLA RIDUZIONE DEGLI ELEMENTI INTERSTIZIALI E STABILIZZANTI SULLE CINETICHE DI RECUPERO E RICRISTALLIZZAZIONE DEGLI ACCIAI INOSSIDABILI FERRITICI E SUPERFERRITICI

AUTHOR/S: R. Guerra*, D.Sciaboletta**, C.Forzanti*, C.Rocchi**, F.Ruffini* * Centro Sviluppo Materiali, Viale B. Brin 219, 05100 Terni (Italia) ** ThyssenKrupp Acciai Speciali Terni, Metallurgia - Sviluppo Tecnologico di Processo e di Prodotto, Viale B. Brin 219, 05100 Terni (Italia) PAPER PRESENTED TO: 33° congresso nazionale AIM - Brescia - 10-12 novembre 2010

ABSTRACT

High chromium ferritic stainless steels are more resistant to stress corrosion cracking in chlorides and caustic alkali media than austenitic grades. Ferritics are usually well resistant to high-temperature oxidation and localized corrosion so they can represent an alternative to the more expensive austenitic stainless steels. Their corrosion resistance can be improved through the reduction of the interstitial element content and the addition of stabilizing elements such as titanium and niobium.

 

Carbon and nitrogen content can be reduced using AOD and VOD converter.  The aim of this work is to evaluate the effect of the interstitial and stabilizing elements on recovery and recrystallization kinetics of ferritic stainless steels in order to define the best process parameters and the microstructure properties achievable in the final products.  According to this, specimens having different interstitial, stabilizing and chromium content and belonging to three different ferritic steels, produced through AOD and VOD cycle, have been analyzed.

 

Laboratory cold rollings have been carried out with two different reductions in order to split the effect of the interstitial content and rolling reduction on recovery and recrystallization kinetics. Both recovery and recrystallization have been evaluated on the base of hardness measures. Laboratory investigations showed that lot of little particles disadvantage the recovery process because reduce the mean free path of dislocations; recrystallization is hindered from the niobium not alloyed in form of carbides or nitrides and is promoted by the presence of little particles that improve the stored deformation energy. Cold rolling reduction has a light influence on the achievable fraction of recovery and recrystallization but affects their kinetics, mostly in the early phase.

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