Frequently Asked Questions for Stainless Steel Surface Treatment Process Stainless steel has excellent properties such as unique strength, high wear resistance, superior corrosion resistance and rust resistance. Therefore, it is widely used in chemical industry, food machinery, electromechanical industry, environmental protection industry, household appliance industry and home decoration, fine decoration industry, giving people a gorgeous and noble feeling.
The development of stainless steel applications will be more and more promising, but the development of stainless steel applications largely determines the degree of development of its surface treatment technology.
1. Common surface treatment methods for stainless steel
1.1 Introduction to stainless steel varieties
1.1.1 Main components of stainless steel: generally contain high-quality metal elements such as chromium (Cr), nickel (Ni), molybdenum (Mo), and titanium (Ti).
1.1.2 Common stainless steel: chrome stainless steel, containing Cr≥12%; nickel-chromium stainless steel, containing Cr≥18%, containing Ni≥12%.
1.1.3 Classification of stainless steel metallographic structure: There are austenitic stainless steels, such as: 1Cr18Ni9Ti, 1Cr18Ni11Nb, Cr18Mn8Ni5. Martensitic stainless steel, for example: Cr17, Cr28, and the like. Generally referred to as non-magnetic stainless steel and with magnetic stainless steel.
1.2 common stainless steel surface treatment methods
Commonly used stainless steel surface treatment technology has the following treatment methods: 1 surface whitening treatment; 2 surface mirror bright treatment; 3 surface coloring treatment.
1.2.1 Surface color whitening treatment: stainless steel is processed in the process of rolling, burring, welding or artificial surface baking and heating to produce black scale. This hard gray-black oxide scale is mainly composed of two kinds of EO4 components, NiCr2O4 and NiF, which were previously removed by strong etching using hydrofluoric acid and nitric acid. However, this method is costly, pollutes the environment, is harmful to the human body, is highly corrosive, and is gradually being eliminated. At present, there are two main methods for treating scales:
(1) Sand blasting (pill) method: mainly by spraying micro glass beads to remove black scale on the surface.
(2) Chemical method: Dipping is carried out using a non-polluting pickling passivation paste and a normal temperature non-toxic cleaning solution with an inorganic additive. Thereby achieving the purpose of whitening treatment of stainless steel color. After processing, it basically looks like a dull color. This method is suitable for large and complex products.
1.2.2 Surface treatment of stainless steel surface Brightening method: According to the complexity of stainless steel products and user requirements, mechanical polishing, chemical polishing, electrochemical polishing, etc. can be used to achieve specular gloss. The advantages and disadvantages of these three methods are as follows:
1.2.3 Surface coloring treatment: stainless steel coloring not only gives various colors to stainless steel products, increases the variety of products, but also improves the wear resistance and corrosion resistance of the products.
There are several methods for coloring stainless steel:
(1) chemical oxidation coloring method;
(2) electrochemical oxidation coloring method;
(3) ion deposition oxide coloring method;
(4) high temperature oxidation coloring method;
(5) Gas phase cracking coloring method.
A brief overview of the various methods is as follows:
(1) Chemical oxidation coloring method: the color of a film formed by chemical oxidation in a specific solution, which is a dichromate method, a mixed sodium salt method, a vulcanization method, an acidic oxidation method, and an alkaline oxidation method. In general, "Inco" (INCO) is used more, but to ensure that a batch of products have the same color, it must be controlled with a reference electrode.
(2) Electrochemical coloring method: the color of a film formed by electrochemical oxidation in a specific solution.
(3) Ion-deposited oxide coloring method: The stainless steel workpiece is placed in a vacuum coating machine for vacuum evaporation. For example: titanium-plated watch case, watch band, usually golden yellow. This method is suitable for processing large quantities of products. Because of the large investment and high cost, small batch products are not worthwhile.
(4) High-temperature oxidation coloring method: in a specific molten salt, the immersed workpiece is kept at a certain process parameter, so that the workpiece forms a certain thickness of oxide film, and presents various colors.
(5) Gas phase cracking coloring method: it is more complicated and less used in industry.
1.3 treatment method selection
Which method is used for the surface treatment of stainless steel, according to the product structure, material, and different requirements on the surface, select the appropriate method for treatment.