Today, Xiaobian will explain to you the material factors that affect the pitting corrosion of seamless square pipes. For seamless square tubes, elements 0, 10 and F are the main alloying elements which make the alloy have good resistance to pitting corrosion. Other elements may also have some effect, while K and other elements will reduce the pitting corrosion resistance of seamless square tubes. It is affirmative that the effect of alloying elements on the pit corrosion resistance of materials can be summarized briefly in terms of beneficial effects. The effects of 13 and 0 are variable. 3 is beneficial in solid solution, but harmful when precipitated as intermediate metal phase, 0 is harmless in solid solution and harmful when precipitated with carbide, but slightly harmful. (2)对奥氏体无缝方管进行冷加工的研究表明，冷加工后试样表面的蚀坑数目增多和蚀坑的尺寸变小。这是因为冷加工增加位错密度，位错在表面露头处容易引起点腐蚀坑，冷加工有增加点腐蚀的趋势。
(2) The research on cold-working of austenitic seamless square tubes shows that the number of pits on the surface of samples increases and the size of pits decreases after cold-working. This is due to the increase of dislocation density in cold processing, dislocation in the surface outcrop is prone to cause pitting corrosion, cold processing has the trend of increasing pitting corrosion.
(3) For a given alloy environment system, the factor that determines the pitting corrosion potential of the alloy is the smoothness of the material surface. In fact, it is meaningless to compare the pitting corrosion tendency of alloys with different surface finish. The effect of surface finish on the corrosion resistance of seamless square pipes is shown in the figure. It shows that in the same material environment system, if the surface finish is different, the difference of pitting corrosion potential can be more than 14.
(4) The oxide formed by heating in seamless square tubes in air may have a significant impact on the pitting corrosion resistance. from
Microstructure galvanized square tubes play an important role in the pitting corrosion resistance of the alloy. Various phases, such as sulphide inclusions and 3 ferrite. Phases, sensitized grain boundaries and welds may have a decisive impact on the pit corrosion resistance of steel. They are the most sensitive sites for pit corrosion. For the cast seamless square tubes with complex microstructures and martensitic seamless square tubes with sensitive microstructures to heat treatment process, the relationship between pitting corrosion and constituent phases is more close. It should be pointed out that the complex manganese sulfide inclusions are more sensitive to pitting corrosion. Therefore, aluminium deoxidizer should be avoided in the smelting of seamless square tubes.
(5) The oxide film produced by welding may be detrimental to the pitting corrosion resistance of the alloy in the strong chloride solution.
(6) The main function of passivation treatment is to dissolve the inclusions and contaminants on the surface of seamless square tubes and make them clean. It can also remove the manganese sulfide inclusions on the surface. Such inclusions may become the origin of pitting corrosion and thus improve the pitting corrosion resistance of seamless square tubes. It should be noted that seamless square tubes are cleaned with sodium hydroxide solution after passivation treatment.
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