Abstract: A bilayer passive film structure of a substrate, comprising an inner layer comprising an oxide of a first element, and an outer layer comprising an oxide of a second element, wherein the passivation potential of the first element is lower than the passivation potential of the second element, and the passivation potential of the second element is lower than the transpassivation potential of the first element. Also a method of forming the above bilayer passive film structure of a substrate, comprising: treating a surface of the substrate containing Cr and Mn. Further a stainless steel comprises, in percentage by weight, 15%<Cr<22%, 13%<Mn<23%, 12%<Ni<23%, and 0.5%<Si<4%, wherein Si can be replaced with an equal amount of Al, Ti or V.

Abstract: The present invention provides a non-magnetic stainless steel with high strength and corrosion resistance and a preparation method thereof. The non-magnetic stainless steel composed of the following components according to percentage by weight: 17%<Cr<23%, 17%<Mn<23%, 17%<Co<23%, 0.5%<Si <3%, and the balance of iron and inevitable impurities thereof. The preparation method includes: (1) melting a raw material and casting it to a mold to obtain a stainless steel block; (2) homogenizing the stainless steel block at 1,100-1,250° C. for 6-12 hours; (3) forging the homogenized stainless steel block at 1,050-1,150° C. with a final forging temperature of 850-950° C. to obtain a plate having a thickness of 5-15 mm; and (4) holding the forged plate at 1,000-1,250° C. for 10-30 minutes and then put it in water for quenching. The non-magnetic stainless steel of the present invention has superior pitting corrosion resistance and mechanical properties.