Stainless steel surface treatment process

 Stainless steel has unique strength and superior anti-corrosion properties. At the same time, it has high wear resistance and is not easy to rust. Therefore, it is widely used in the chemical industry, food machinery, electromechanical industry, and household appliance industry. The application and development prospects of stainless steel will become wider and wider, but the application and development of stainless steel largely determine the degree of development of its surface treatment technology.

Introduction of stainless steel varieties

Stainless steel generally contains high-quality metal elements such as chromium (CR), nickel (NI), molybdenum (MO), and titanium (TI). Common stainless steels include chromium stainless steel and nickel-chromium stainless steel. Classification from the metallographic structure of stainless steel: austenitic stainless steel, martensitic stainless steel

Stainless steel surface treatment varieties

• Whitening treatment of the natural color of the surface
• Surface mirror stone bright treatment
• Surface coloring treatment

1. The surface natural color whitening treatment

In the process of processing, the stainless steel undergoes coiling, edge binding, welding, or the handler’s warm surface fire treatment, resulting in a black oxide scale. This kind of hard gray-black oxide scale was usually removed by a strong corrosion method with hydrofluoric acid and nitric acid in the past. However, this method is costly, pollutes the environment, and is harmful to the human body. The corrosion is relatively large, and it is gradually eliminated.

At present, there are two kinds of treatment methods for this kind of oxide scale: (1) Using shot peening/sandblasting method. (2) Use chemical methods.

2. Mirror bright treatment method of stainless steel surface

According to the complexity of stainless steel products and the different requirements of users, mechanical polishing, chemical polishing, electrochemical polishing, and other methods can be used to achieve mirror stone luster.

Mechanical polishing

Good leveling performance, bright labor intensity, serious pollution, difficult to process complex parts, reduced gloss, high investment, and cost. Simple workpieces, medium and small products, and complex parts cannot be processed. The gloss of the entire product is not consistent, and the gloss retention time is not long.

Chemical polishing

Low investment, complex parts can be polished, high efficiency, high speed, insufficient brightness, polishing liquid to be humidified, gas overflows, and wind-friendly equipment is required.

Electrochemical polishing

Mirror gloss, long-term maintenance, stable process, less pollution, low cost, and good anti-pollution performance. The one-time investment is large, and the complicated parts must be equipped with tooling and auxiliary electrodes.

3. Surface coloring treatment

Stainless steel coloring not only imparts various colors to stainless steel products, increases the variety of products, but also improves the wear resistance of products.

There are several coloring methods for stainless steel:

(1) Ion deposition of oxides or oxides

(2) High-temperature oxidation method

(3) Chemical oxidation method, electrochemical oxidation method

(4) Gas-phase cracking method

Briefly describe the overview of various methods:

(1) The ion deposition oxide or oxide method is to place the stainless steel workpiece in a vacuum coating machine for vacuum evaporation plating; this method is suitable for mass product processing. Because of the large investment and high cost, small-batch products are not economical.

(2) The high-temperature oxidation method is to immerse the workpiece in a specific molten salt to maintain a certain process range, so that the workpiece forms a certain thickness of oxide film, and presents a variety of different colors.

(3) The chemical method is to form the color of the film through chemical oxidation in a specific solution. However, if the color of a batch of products is consistent, it must be controlled by a reference telegram.

(4) The electrochemical method is to form the color of the film through electrochemical oxidation in a specific solution.

(5) The gas-phase cracking method is more complicated and less used in industry.