Vliv titanu a niobu na stabilitu pasivního stavu austenitických korozivzdorných ocelí

Abstract

Production of low-carbon austenitic types of stainless steel is widely deployed and the carbon content can be reduced to below 0.02%. But even such a low carbon content is not sufficient for long-term use of austenitic steels at elevated temperatures. Although the maximum amount of 0.03% carbon and titanium and niobium stabilization gives promising results in terms of reducing susceptibility to intergranular corrosion, does not fully question the long-term use in the critical temperature and susceptibility to stress corrosion cracking particularly in relation to low temperature zcitlivěním. In nuclear energy at temperatures around 300 ° C for the selection of steel is mainly stabilized austenitic stainless steel and carbon steel, with a balanced chemical composition, derived for a minimum period of heating in the critical temperature and the amount of carbon and chromium, even taking into account the mechanical characteristics and resistance to stress corrosion cracking. This thesis was aimed to study the problem of stability of passive state of austenitic stainless steels, titanium and niobium stabilized. To assess the influence of these elements in solid solution was the type of low-carbon austenitic steels 02Cr18Ni12 and 02Cr18Ni14Mo2,5 with graded levels of titanium and niobium refined electrochemical potentiodynamic polarization method. In addition, these steels were subjected to testing resistance spot corrosion and stress corrosion. The work performed and the attendant results we can say that outlined a broad problem of stability of the passive state in stabilized austenitic stainless steels and titanium in a positive effect compared with niobium. In a continuation of this work would be appropriate to focus on larger quantities of differentiation alloying elements in steels and the structural homogeneity of the experimental heats.