How Are Colored Stainless Steel Sheets Made?

The manufacturing process of colored stainless steel sheets is a sophisticated combination of precision metalworking and advanced surface treatment technologies. The primary goal is to impart durable, aesthetically pleasing, and diverse colors onto the stainless steel substrate while preserving its excellent physical and chemical properties, such as strength and corrosion resistance. Foshan Xinliheng Oțel inoxidabil Co., Ltd., as a professional stainless steel processor, primarily employs Physical Vapor Deposition (PVD), the mainstream and technically mature method in the industry today.

Below is the typical production process for colored stainless steel sheets, focusing on the PVD technique:

1. Preparation and Substrate Treatment

This step is crucial for ensuring a uniform final color and strong adhesion of the coating.

• Raw Material Selection: High-quality stainless steel coils or sheets are selected as the base material. Common grades include 304 şi 316, chosen based on the final application.
• Slitting/Cutting: The stainless steel coil is leveled and cut into flat sheets of the required dimensions.
• Surface Pre-treatment:
  • Degreasing and Cleaning: Chemical or ultrasonic cleaning is used to thoroughly remove oil, grease, dust, and other contaminants from the sheet’s surface.
  • Surface Polishing: The surface is processed to achieve the desired base texture, which determines the final visual effect.
    • Oglindă (8K): Achieved through high-precision grinding and polishing, resulting in a mirror-like finish.
    • Fire (Brushed): Created by mechanical brushing, producing a uniform linear texture.
    • Satin/No.4 (Matte): Formed by blasting abrasive particles, resulting in a uniform matte or fine sand finish.
    • Gravat: Achieved through chemical or laser etching, creating specific patterns or textures on the surface.

2. Core Coloring Process – Physical Vapor Deposition (PVD)

This is the central step where the colored coating is formed, typically carried out in a vacuum environment.

• Vacuum Coating: The pre-treated stainless steel sheet is placed into a large vacuum coating chamber, which is then evacuated to a high vacuum state.
• Evaporation/Sputtering: Inside the vacuum, the target metal (such as titanium, zirconium, chromium, or gold) or its compounds are heated via arc, electron beam, or magnetron sputtering until they evaporate or sputter.
• Ionization and Deposition: The evaporated or sputtered metal atoms react with introduced reactive gases (such as nitrogen N₂, oxygen O₂, or acetylene C₂H₂) in the vacuum, forming ions of metal compounds (e.g., titanium nitride TiN, zirconium oxide ZrO₂, titanium carbide TiC). Under the influence of an electric field, these ions bombard and deposit uniformly onto the stainless steel surface, forming a dense, nanoscale-thin film with exceptional adhesion.
• Color Formation Principle: The color is determined by the thickness and composition of the deposited layer. This is not a pigment-based “inherent color,” but rather utilizes the principle of light interference. When light hits this thin film, part of the light reflects off the film’s surface, while another part passes through the film and reflects off the stainless steel substrate. These two reflected light waves interfere with each other. By precisely controlling the film’s thickness (typically tens to hundreds of nanometers), the wavelengths of light that are enhanced or diminished by interference can be regulated, resulting in different colors. For example:
  • Titanium nitride (TiN) films of varying thicknesses can appear gold, champagne, rose gold, or black.
  • Multi-layer deposition or adjusting the gas mixture can produce a wider range of colors, such as blue, green, purple, or iridescent effects.

3. Post-Processing and Quality Control

• Cooling: After coating, the sheets are slowly cooled to room temperature inside the vacuum chamber.
• Inspection: Rigorous quality checks are performed on the finished product, including:
  • Visual Inspection: Checking for color uniformity, color differences, scratches, spots, or other defects.
  • Performance Testing: Testing coating adhesion (e.g., cross-cut test), abrasion resistance, corrosion resistance (e.g., salt spray test), and weatherability.
• Protective Film Application: To protect the delicate colored surface during transportation and fabrication, a protective film (PE film) is usually applied to the sheet’s surface.
• Packaging and Storage: The sheets are packaged according to customer requirements and then stored or shipped.
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Other Coloring Methods (Supplementary Information)

While PVD is the dominant high-end process, other coloring methods exist in the market, though they are generally less common and may not match PVD in performance:

• Chemical Coloring: Immersing stainless steel in specific chemical solutions to generate oxide films of varying thicknesses through chemical reactions, which produce color. This method is lower in cost but offers limited color options and inferior durability and abrasion resistance.
• Electroplating: Depositing a layer of another metal (such as copper, nickel, or chromium) onto the stainless steel surface via electroplating to change its color. The process is well-established but faces environmental pressures, and the coating’s adhesion and corrosion resistance may be inferior to PVD.
• Spraying: Applying colored paint or powder coating to the surface. This is low-cost with a wide range of color choices, but the coating’s durability, abrasion resistance, and texture are significantly inferior to PVD, and there are risks of peeling and environmental concerns.

Summary: Modern high-quality colored stainless steel sheets, especially those used in architectural decoration and high-end furniture, rely on the PVD vacuum coating process as their core manufacturing technique. This complex process demands high-precision equipment, controlled environments, and stringent process control. However, it produces high-end decorative materials with vibrant, durable, wear-resistant, and environmentally friendly finishes. Professional companies like Xinliheng achieve market recognition for brands like “Haoliang” through their mastery of these processes and rigorous quality control.