What are the material factors that affect the pitting corrosion of seamless rectangular tubes.
(1) For seamless rectangular tube, 0, 10 and F are the main alloy elements which make the alloy have good pitting corrosion resistance. Some other elements may also have certain effect, while K and other elements will reduce the pitting corrosion resistance of seamless rectangular tubes. It is certain that the effect of alloying elements on the point corrosion resistance of materials can be summarized as favorable effects. 13. The effect of 0 is variable. 3 is beneficial in solid solution, but harmful when it is precipitated as intermediate metal phase, 0 is harmless in solid solution, and harmful when precipitated as carbide, but it has slightly adverse effect.
(2) The study on cold working of austenitic seamless rectangular tube shows that the number of etch pits on the surface of specimens increases and the size of pits decreases after cold working. The reason is that the density of dislocations is increased by cold working, and the pitting corrosion pits are easily caused by dislocations at the surface outcrop.
(3) For a given alloy environment system, the factor that determines the spot corrosion potential of the alloy is the surface finish of the material. In fact, there is no point in comparing the surface finish of the alloy. The effect of surface finish on the pitting corrosion performance of seamless rectangular tube is shown in the figure. It shows that in the same material environment system, if the surface finish is different, the difference of point corrosion potential can be more than 14.
(4) The oxide formed by heating may have a significant effect on the pitting corrosion resistance of seamless rectangular tube in air. from
The microstructure of hot-dip galvanized square tube plays an important role in the pitting corrosion resistance of the alloy. Various phases, such as sulfide inclusions, 3 ferrite. The phase, the sensitized grain boundary and the weld may have a decisive influence on the pitting corrosion resistance of the steel. They are all sensitive parts of pitting corrosion. The relationship between pitting corrosion and phase composition is more close for casting seamless rectangular tube with complex microstructure and martensitic seamless rectangular tube whose microstructure is very sensitive to heat treatment process. It should be pointed out that the composite manganese sulfide inclusions are more sensitive to pitting corrosion. Therefore, aluminum deoxidizer should be avoided in smelting seamless rectangular tube.
(5) The oxidation film produced by welding may be detrimental to the pitting corrosion resistance of the alloy in strong chloride solution.
(6) The main function of passivation treatment is to dissolve the inclusions and contaminants on the surface of seamless rectangular tube to make it clean. It can also remove the manganese sulfide inclusion on the surface, which may become the source of pitting corrosion and improve the pitting corrosion resistance of seamless rectangular tube.