Molybdenum Used In Stainless Welded Steel Pipe Manufacture
Research has confirmed that in sea atmosphere environment, it is hard to completely prevent the corrosion of stainless steel plate when only use chromium, even with high chromium content nearly 24%. Molybdenum elements must be added. But the premise of the beneficial effects of molybdenum on the corrosion resistance of stainless steel plate is the steel must contain adequate amounts of chromium elements. And with the increase of chromium content in steel, the beneficial effects of molybdenum also will increase significantly.
Molybdenum can significantly promote the enrichment of passivation membrane, thus to improve the stability of the passivation membrane of stainless steel welded pipe, increase of chromium in steel corrosion, so as to greatly improve all kinds of stainless steel resistance and the corrosion resistance of various kinds of reducing acid medium. With the H2SO4 concentration increased, in order to obtain the molybdenum content of the corrosion rate should be increased. For corrosion resistance, concentration of 50% - H2SO4 need more molybdenum than concentration was 75% - H2SO4, because 50% - H2SO4 is more corrosive.
Molybdenum can improve the passivation ability of in the stainless steel welded pipe, the pitting and crevice corrosion resistant ability is about 3 times of chromium, for the goodness of resistance to pitting and crevice corrosion, stainless steel plate need to be added with molybdenum. Molybdenum is to prevent pitting as the origin of the stress corrosion. Among some corrosive mediums, molybdenum molybdate formed after the corrosion of the stainless steel have been confirmed by experiment. Molybdenum can promote precipitation of intermetallic compounds sigma, χ, etc, thus reducing the organization thermal stability of the stainless steel welded pipe, increase the embrittlement sensitivity, and reduce steel plastic, toughness, corrosion resistance and cold formability and weldability.
Molybdenum can improve the strength of the stainless steel welded pipe, including high temperature strength, makes improvements of high temperature lasting and creep properties. But with the increase of amount of molybdenum, high temperature deformation resistance of stainless steel increases, thermoplastic property decreased, at the same time molybdenum promote the formation of ferrite of austenitic stainless steel, these factors all can lead to bad performance in steel hot working and heat formability.
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