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Common Issues in Stainless Steel Surface Treatment and Preventive Measures
Stainless steel boasts unique strength, exceptional wear resistance, superior corrosion protection, and the remarkable advantage of being rust-resistant.
2019-01-17
Stainless steel boasts unique strength, exceptional wear resistance, superior corrosion protection, and an inherent resistance to rusting—qualities that make it highly versatile. As a result, it is widely used in industries such as chemical engineering, food machinery, electrical and mechanical equipment, environmental protection, home appliances, home décor, and decorative applications, lending a sense of grandeur and elegance to any setting.
The application prospects of stainless steel will continue to expand, but the development of stainless steel applications largely determines the advancement of its surface treatment technologies.
1. Common Methods for Stainless Steel Surface Treatment
1.1 Introduction to Stainless Steel Grades
1.1.1 Main components of stainless steel: Typically contains high-quality metallic elements such as chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and more.
1.1.2 Ordinary Stainless Steel: Chromium stainless steel containing 12% or more chromium; and nickel-chromium stainless steel containing 18% chromium and 12% nickel-chromium.
1.1.3 The microstructural types of stainless steel are categorized as follows: Austenitic stainless steels, such as 1Cr18Ni9Ti, 1Cr18Ni11Nb, and Cr18Mn8Ni5; and Martensitic stainless steels, including grades like Cr17 and Cr28, commonly referred to as either non-magnetic or magnetic stainless steels.
1.2 General Surface Treatments for Stainless Steel
Common surface treatment techniques for stainless steel include: 1) Whitening treatment of the natural surface color; 2) Mirror-like whitening treatment of the surface; 3) Surface coloring treatment.
1.2.1 Surface Whitening Treatment: During stainless steel processing, black oxide scale is formed through rolling, edge sealing, welding, or manual surface heating treatments. This hard, gray-black oxide scale primarily consists of NiCr₂O₄ and NiFeO₄. Traditionally, strong corrosive agents like hydrofluoric acid and nitric acid were commonly used to remove it effectively. However, this method is costly, environmentally harmful, poses risks to human health due to its high corrosivity, and is gradually being phased out. Currently, there are two main approaches for treating the oxide scale:
(1) Sandblasting (or Shot Blasting): Primarily uses glass bead spraying to remove the black oxide scale from the surface.
(2) Chemical Method: This method employs a non-polluting acid passivation paste and a room-temperature, non-toxic cleaning solution containing inorganic additives for leaching. The goal is to achieve a brightening effect on the stainless steel. After treatment, the surface will essentially appear dark in color. This approach is particularly well-suited for large, complex products.
1.2.2 Stainless Steel Surface Mirror Polishing Treatment: Depending on the complexity of the stainless steel product and user requirements, methods such as mechanical polishing, chemical polishing, and electrochemical polishing can be employed to achieve a mirror-like luster. The advantages and disadvantages of these three methods are outlined below:
1.2.3 Surface Coloring Treatment: Coloring stainless steel not only imparts a variety of colors to stainless steel products, expanding the range of available items, but also enhances their wear resistance and corrosion resistance.
There are several methods for coloring stainless steel:
(1) Chemical oxidation coloring method;
(2) Electrochemical oxidation coloring method;
(3) Ion deposition oxidation coloring method;
(5) High-Temperature Oxidation Coloring Method;
Gas-phase pyrolysis coloring method.
A brief overview of the various methods is as follows:
(1) Chemical Oxidation Coloring Method: In specific solutions, the color of the film is formed through chemical oxidation, including the dichromate method, mixed sodium salt method, sulfidation method, acid oxidation method, and alkali oxidation method. Generally, INCO is widely used, but if you want to ensure that a batch of products has the same color, you must use a reference electrode for precise control.
(2) Electrochemical Coloring: The color of the film is formed through electrochemical oxidation in a specific solution.
_Ion-deposition oxide coloring chemical method: This involves placing stainless steel components into a vacuum coating machine for vacuum evaporation coating. For example, titanium-plated watch cases and straps are typically finished in gold tones. This method is well-suited for processing large-scale production runs. However, due to its substantial investment and high costs, it becomes economically impractical for small-batch products.
(4) High-Temperature Oxidation Coloring Method: In a specific molten salt, the workpiece is immersed under defined process parameters, allowing it to develop an oxide film of a certain thickness and exhibit a variety of distinct colors.
Gas-phase pyrolysis coloring method: Relatively complex and less commonly used in industrial applications.
1.3 Selection of Treatment Methods
Stainless steel surface treatment should be selected based on the product's structure, material quality, and specific requirements for the surface.
2. Common Causes of Corrosion in Stainless Steel Parts
2.1 Chemical Corrosion
2.1.1 Su
Stainless steel,Wear-resistant,Anti-corrosion
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