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The influence of the ferritic and austenitic phases and of silicon on the Corrosion resistance of alloyed cast steels
Author(s) -
Vehovar L.,
Godec B.
Publication year - 1995
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19950460903
Subject(s) - corrosion , materials science , tafel equation , overpotential , metallurgy , austenite , cathodic protection , silicon , electrochemistry , carbon steel , anode , microstructure , electrode , chemistry
The paper deals with the influence of the α/gamma; phase ratio and silicon on the corrosion resistance of low carbon alloyed cast steels in strongly oxidizing media. Electrochemical investigations in 65% HNO 3 + 5g Cr 6+ ions/I showed that none of the four tested cast steels, with γ R = 100%, γ R = 75%, γ R = 50% and γ R = 0%, achieved a passive state, and that the corrosion process was under cathodic control. Under such conditions the calhodic activation overpotential is considerably greater than the anodic activation overpotential, and, as well as this, the Tafel coefficient for a cathodic reaction has higher values than those which are characteristic for an anodic reaction. The austenitic cast steel is the most resistant to corrosion, since for the corrosion process to take place the greatest activation energy is needed. The results of investigations of corrosion resistance in 12M HNO 3 , at 115°C, for 240 hours, confirmed the results of the electrochemical measurements and the predominant role of the austenitic cast steel with γ R = 100%. By means of AES analysis it was found that the good resistance to corrosion of such a cast steel is based on the building up of a thin mechanically‐protecting barrier, which mainly consists of silicon.