Solid Base Pan Material Improvements

In caustic soda industry, produce solid soda from soda solution by means of evaporation and using of caustic soda concentration pot is a common method at present and in future. The market prospect of caustic soda concentration pot is pretty good. Under a little increase of cost, the corrosion resistance can be increased, as a result, the service life of caustic soda concentration pot can be raised. This can result in good economic effect of caustic soda concentration pot manufacturer and social benefit.This article analyzed the corrosion mechanism and failure style of cast iron on the basis of basic theory of corrosion of "cast iron taking the soda concentration pot used widely in caustic soda industry as the subject investigated, and studied the methods and measures to be taken to improve the local corrosion resistance of soda concentration pot. According to the different working conditions of soda and potash, three and two compositions were designed respectively on the basis of the original 1# basic iron, and comparison tests were carried out in contrast with the 1# basic iron. After mechanical property test, metallographic structure test, uniform corrosion test and caustic embrittlement resistance test, the alkali resistances were compared. Through analysis of chemical composition, metallographic structure, mechanical property and alkali resistance of different cast iron, and based on the practices, it is believed that the configuration of graphite in the cast iron has an inconspicuous effect on the general corrosion resistance, while it has an obvious effect on the caustic embrittlement resistance. The alkali resistance of cast iron of single pearlitic structure is better than that of cast iron of a combined structure of pearlite and ferrite. Under the soda conditions, the all round properties in respect of alkali corrosion of 1# basic iron after inoculation and modification by adding kaiium and sodium modifier (3# test piece) are much better than that of 1# basic iron.Because the cast iron is inoculated and modified, a great amount of crystal nucleus are added into the molten cast iron, so the solidification process is improved and fine metallographic structure is acquired and also the mechanical properties and corrosion resistance are increased. After modification and inoculation treatment, the tensile strength is increased from 207 MPa to 220 MPa, graphite size is improved from grade 5 to grade 4, uniform corrosion loss is decreased from 1.15 gram per piece to 0.98 gram per piece, the number of times of water quench during anti-caustic embrittlement property test is increased from 47 to 78. While under potash conditions, the all round properties in respect of alkali corrosion of 1# basic iron after adding 0.3-0.5% Cr without adding manganese (5#and 6# test pieces) are much better than that of 1# basic iron (1# test piece).Because of addition of alloy element Cr, the base structure is fined, the pearlite phase is stabilized, the property of the surface passivation film of the material is improved. As no ferromanganese is added, the manganese content is reduced, so the segregations at grain boundary is reduced. This results in increase of mechanical properties, and corrosion resistance of the material. The tensile strength is increased from 213 MPa to 246 MPa, uniform corrosion loss is reduced from 1.97 gram per piece to 1.45 gram per piece, the number of times of water quench during anti-caustic embrittlement test is increased from 33 to 60. These two kinds of materials are both developed from 1# basic iron after modification. For their simple fabrication processes and low costs, the use of these materials for soda concentration pots are worthy of extension.