Many manufacturers to reflect, in the use of cast iron valve, idle valve processing is not good, so the next time the rust or corrosion, do not know how to solve, let a person very headache. Reflection for manufacturers, our company has made some principle of the analysis, as well as some solutions, hope to those who need help.
The relevant factors of iron corrosion and chemical composition, microstructure, parts of the surface characteristics, but also with etching medium composition, lively and temperature and other relevant factors. The corrosion rate of iron in the atmosphere is very slow, with the extension of time, the casting surface will form a layer of protective film, so that the alloy from active state to the passive state, significantly reduce the corrosion rate of iron in the atmosphere. In the alloy cast iron has the obvious boundary, as a result of special carbides and other compounds precipitate along the grain boundary, alloy element solid solution containing reduced, prone to corrosion along grain boundaries between crystallites, which makes a hole or reduce the strength of cast iron.
According to the properties of rubber, the processing characteristics of strong toughness. The tool so that the processing of rubber before and after angle than the cutting tool in machining metal before and after angle large. Tool material selection for W18Cr4V. Machining. Must promptly remove rubber scraps, otherwise the effect of surface roughness. Corrosion of cast iron valve corrosion mechanism of cast iron usually chemical or electrochemical corrosion, which may be the uniform state, local, and intergranular stress. The requirements of corrosion should be uniform, because corrosion local stress, and intergranular damages is dangerous.
Some of the information presented, cast iron inoculated in weak medium in general than the ordinary gray cast iron with high corrosion resistance. Under the condition of room temperature, inoculation of cast iron in sulphuric acid, the stability and low alloy cast iron with the same. In 15% ~ 510% stability of acetic acid in the ratio of low nickel cast iron is 115 times higher. To some extent, can be used as a substitute for low alloy cast iron. Ability of cast iron valve corrosion prevention measures to improve the seawater corrosion resistant cast iron, the best way is to use inoculated cast iron (Table 1) with proper alloying to solve. Such as the HT250Ni2 microstructure is fine lamellar pearlite > 98%,, 75% ~ 90% for the flake graphite, length of 30 ～ 120 μ m, two yuan of phosphor eutectic < 1%, into a single pearlite, grain boundaries without carbide precipitation, effectively avoid the grain boundary corrosion, according to the provisions of GB 9439, N grade of grey cast iron, the tensile strength of N - (n + 100), the tensile strength is 250 ~ 350 MPa, the pressure can be fully guaranteed. Also after inoculation of molten iron, not only the matrix evenly, and internal stress decreased significantly, can avoid the stress corrosion
According to the electrochemical corrosion theory, the ideal structure is single phase and homogeneous microstructure, so pure, Ferritic and austenitic steel, when the other conditions are the same, has high corrosion stability. But a single cast iron microstructure is impossible, only consider the microstructure homogenization to improve corrosion resistance.
We can see from the above, the corrosion of cast iron valve is chemical or electrochemical corrosion, the state is not the same. Know why these principle, in order to obtain methods treat a root, solve the problem to solve.
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