β Scribed by Prof. Dr. L. Vehovar; B. Godec
No coin nor oath required. For personal study only.
The paper deals with the influence of the Ξ±/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 Ξ³~R~ = 100%, Ξ³~R~ = 75%, Ξ³~R~ = 50% and Ξ³~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 115Β°C, for 240 hours, confirmed the results of the electrochemical measurements and the predominant role of the austenitic cast steel with Ξ³~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 mechanicallyβprotecting barrier, which mainly consists of silicon.
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