Nanocrystalline material based on stainless steel surface, and preparation method therefor

A method for preparing a nanocrystalline material, characterized in that the method comprises the following steps:

• (1) chemically degreasing and etching with alkali a stainless steel surface using a sodium hydroxide solution and a solution containing an alkali etching active agent at 80-85° C. for 10-15 minutes, followed by washing with water;
• (2) oxidizing the stainless steel surface treated in the step (1) by an oxidizing solution containing 200-300 g/L of CrO3 and 100-150 g/L of Na2MoO4 with a temperature of 75-90° C. and a pH of 0.4-1.5, followed by washing with water;
• (3) immersing the stainless steel surface treated in the step (2) as a cathode in an electrolyte containing 100-150 g/L of CrO3, 100-150 g/L of Na2MoO4, 200-250 g/L of H3PO4, and 50-60 g/L of Na2SiO3 to electrolyze, followed by washing with water;
• and
• (4) placing the stainless steel surface treated in the step (3) at a temperature of 50-60° C. and a humidity of 60-70% for hardening for 3-4 hours;
• expressed in percentage by weight, the nanocrystalline material contains 0-3% of carbon, 20-35% of oxygen, 40-53% of chromium, 10-35% of iron, 1-4% of molybdenum, 1-4% of nickel, 0-2.5% of silicon, 0-2% of calcium with the balance being impurity elements;
• and
• wherein in the step (3), a current for the electrolyzing is direct current;
• an intensity of the current is 40-5 A/m2;
• an initial current intensity is 40 A/m2, and then the initial current intensity is gradually reduced to 5 A/m2 according to the formula i=3+A/t, wherein i is current intensity, t is time, and A is parameter of 20-30;
• and the time for the electrolyzing is 25-55 minutes.