Research On Corrosion Of Cast Iron Materials In Water Environment Including Seawater, Freshwater, Salt Lake Brine And Salt Solution

It is well known that human life and production building are dependent on natural water resources. The development and utilization of natural water resources, such as offshore oil drilling and the construction of gas exploitation device, large potash fertilizer manufactory in salt lake and The Grand Three Gorges Project, which are dependent on metal materials. Among the metal materials, iron material has attracted much attention because of its low price, good casting and machining performance. So, study on the corrosion data of cast iron in the water environment, master of corrosive regularity and the methods of controlling corrosion are of great practical significance to extend the life of cast iron in water environment, guarantee the safe use of cast iron, promote the development and utilization of water resources.In this paper, the corrosion of cast iron in the water environment including seawater, freshwater, salt lake brine and salt solution are studied on the base of previous researches. Corrosion rates of cast iron immersed in seawater, freshwater, salt lake brine and salt solution are investigated by weight-loss method. The pattern and composition of corrosion products in the water environment are investigated by SEM and XRD respectively. The material performance and characteristics of water environment are investigated by pH, conductivity meter, hardness and tensile test respectively.Corrosive regularity and characteristics of cast iron in the seawater, freshwater, salt lake brine and salt solution are analyzed systematically. The corrosion form of cast iron in seawater, freshwater, salt lake brine and salt solution is mainly oxygen absorption corrosion. The corrosion rates are impacted on limit diffusion current of oxygen. The prime reasons that the difference of corrosion rates of the same material in different environment are the density of oxygen, electrical conductivity and flowing speed. The compositions of corrosion product are iron hydroxide and iron oxide. The effects of low alloying treatment on homogeneous corrosion properties of cast irons in seawater is not obvious. But the pitting corrosion properties of low alloyed cast irons is the most serious on the contrary. The compositions of corrosion product of cast irons in seawater are lepidocrocite (γFeOOH), goethite (αFeOOH) and Fe(OH)3. The oxide film is loose. So, its protection of the cast iron is poor. The average corrosion rate of gray cast iron is the highest and the pitting corrosion of spheroidal graphite iron is the most serious in freshwater of changjiang river. The compositions of corrosion products of spheroidal graphite iron are iron hydroxide, iron oxide with spinel structure and graphite (C). This film of corrosion products can reduce iron corrosion rate in the flowing water because of its high hardness. The corrosion rate of cast iron in salt lake brine is less than the rate in seawater and fresh water. The corrosion rate of spheroidal graphite iron is the smallest only 0.023mm/a. The main factor for good corrosion resistance of spheroidal graphite iron is its own organizational characteristic. The high chloride ion concentration does not reduce the pitting corrosion of cast iron. The corrosion rate on cast iron decreases with the increase of consistency of salt solution when the concentration above 3%. The cast iron has the typical"graphitization"phenomenon. The augment of concentration of salt solution reduces density of the presence of oxygen. But the increment of electric resistance in it will make the electrochemical corrosion current lower. Those are prime reasons that the cast iron corrosion rate decreases.