corrosion-resistant cast iron

Corrosion-resistant cast iron refers to special cast iron that can prevent or delay the corrosion of certain corrosive media. From the perspective of chemical composition, corrosionresistant cast iron belongs to alloy cast iron. In addition, corrosion resistant cast iron can be classified according to the metallographic structure, alloy composition and applicable media. In common corrosive media, the chemical composition of cast iron has a more significant impact on corrosion resistance than its metallographic structure. Therefore, it is usually classified according to the chemical composition of cast iron.



The corrosion of cast iron refers to the process in which it undergoes chemical or electrochemical reaction with its surrounding medium or is eroded by molten metal, which causes its damage or destruction. The corrosion medium of cast iron is generally conductive electrolyte, so the corrosion of cast iron is mostly electrochemical corrosion. The inhomogeneity of the composition, structure (different phases, grain boundaries, lattice defects) and surface state (stress, strain) of the cast iron surface has different electrode potentials, the positive one is the cathode, and the negative one is the anode . The positive and negative electrode potential can only measure the size of the electrochemical corrosion tendency, but can not estimate the corrosion resistance of cast iron. The corrosion resistance depends on the corrosion reaction speed.

The main way to improve the corrosion resistance of cast iron is to add alloying elements to obtain a favorable structure and form a good protective film. In order to increase the corrosioinresitance ability, we can add ferro-alloys with various elements, like ferrosilicon, ferrochrome, metallurgical silicon carbide, etc.  The matrix structure of cast iron is preferably a dense and uniform single-phase structure. Graphite of medium size but not coherent is beneficial to improve corrosion resistance. As for the shape of graphite, it is better to be spherical or flocculent. Improving the corrosion resistance of cast iron is mainly through adding Si, Al, Cr, Ni, Cu, Mo and other alloying elements. The addition of alloying elements Cr, Mo, Cu, Ni, Si, etc. can increase the electrode potential of the cast iron matrix; at the same time, the addition of Si, Al, Cr, etc. can form a dense, complete and strong protective film on the surface of the cast iron; in addition, adding The alloying elements can also improve the shape, size and distribution of graphite in the cast iron structure to reduce the number of galvanic cells and reduce the size of the electromotive force to improve the corrosion resistance of cast iron.