Research On Caustic Corrosion Resistance Of Alloy Cast Iron Of Rare-earth Addition

The reserves of natural base is abundant in Inner Mongolia, the industry which uses natural base to make sodium hydroxide is an important industry, but the corrosion problem of equipments is very serious in the process of making sodium hydroxide, not only lots of metal materials are consumed, but also the cost of production is increased, which restricts the development of basic industry. So, it is very important to develop and exploit new types of materials of corrosion resistance.In this paper, two types of alloy cast iron were designed, including low alloy cast iron of rare-earth addition and medium alloy cast iron of rare-earth addition. The corrosion behavior in the caustic soda was researched, the corrosion rate was tested by the methods of static weight-loss and the corrosion grade was evaluated. The graphite form was observed by an optical microscope, the metallurgical structure was analyzed and the matrix structure was defined by an x-ray diffraction instrument. The corrosion products were observed and the content of elements was analyzed by the SEM and the corrosion resistance mechanism of the alloy cast iron of rare-earth addition in the caustic soda was discussed.The results showed that the matrix structure of these two types of alloy cast iron was refined and the graphite form was changed with the increase of rare-earth content. At the same time, when the rare-earth content was beyond some content, the chilling tendency was serious. The caustic corrosion resistance performance of low alloy cast iron of rare-earth addition with 0.06%RE and medium alloy cast iron of rare-earth addition with 0.05%RE is better under the different corrosion conditions. Becaruse more compact corrosion products were formed on the surface of test specimen RD3 and RZ3, which seperated the materials and alkali liquor and protected the matrix.