There are many method to improve corrosion resistance of stainless steel tube, such as surface coating a layer of corrosion resistant metal, coating nonmetal layer, electrochemical corrosion protection and change of environmental media, etc. But using the alloying method, improve the corrosion resistance of the material itself is one of the most effective measures to prevent the damage of corrosion, the method is as follows:
(1) adding alloying elements, improve the electrode potential of the steel substrate, so as to improve the electrochemical corrosion resistance of stainless steel pipe. General steel adding Cr, Ni, Si more elements can improve the electrode potential. Because Ni is short of, the amount of Si to join can make steel brittle, therefore, only improve the steel substrate electrode potential Cr is common elements.
Cr can improve the electrode potential of steel, but it is not a linear relationship. Experiment proved that steel electrode potential with the increase of alloy elements, there is a quantitative change to qualitative change, follow the 1/8 rule. When the Cr content reaches a certain value when the 1/8 atoms (l / 8, 2/8, 2/8...) There will be a mutation, the electrode potential. As a result, almost all of the stainless steel, the Cr content are in 12. % (atomic) above, more than 11.7% (mass).
(2) adding alloying elements to form a layer on the surface of the steel stable, complete with steel matrix solid membrane purification. To improve the ability of resistance to chemical corrosion of stainless steel tube. Such as Cr in steels, Si, Al alloy elements, such as surface of stainless steel tube to form a dense Cr2O3, SiO2, Al2O3, such as oxidation film, can improve the corrosion resistance of stainless steel pipe.
(3) adding alloying elements to make steel at room temperature can exist in single phase state, reduce the number of micro battery so as to improve the corrosion resistance of steel. Like to join a sufficient number of Cr or Cr - Ni, single-phase ferritic steel at room temperature to obtain or single phase austenite.
(4) to join the elements such as Mo, Cu, improve the ability of corrosion resistance.
(5) join Ti, Nb elements, such as elimination of Cr intergranular segregation, thus reduce the tendency to intergranular corrosion.
(6) to join the Mn, N elements, such as single-phase austenitic organization instead of part of the Ni, at the same time can greatly improve the corrosion resistance of stainless steel pipe in organic acids.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)
