Surface roughness of stainless steel
Stainless steel, as a material widely used in construction, industry, medical care and home furnishing, its surface characteristics directly affect its performance and appearance. Among them, surface roughness is one of the important indicators for measuring the surface quality of stainless steel. This article will take you through what the surface roughness of stainless steel is, its significance, and how to control and optimize it.
Common stainless steel surface roughness range
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Processing technology
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Ra range (μm)
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Surface characteristics
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Application scenarios
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Mirror polishing
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≤0.05 ~ 0.1
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Mirror-like smooth, high reflectivity
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High-end decoration, medical equipment, food equipment
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Fine polishing
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0.1 ~ 0.4
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Delicate and smooth, no obvious texture
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Kitchen utensils, precision instruments
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Mechanical polishing
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0.4 ~ 1.6
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Slightly visible texture, smooth feel
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Architectural decoration, chemical containers
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Wire drawing
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0.2 ~ 1.5
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Unidirectional stripes, matte texture
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Home appliance panels, elevator decoration
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Sandblasting
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1.0 ~ 6.3
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Uniform frosted surface, matte
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Industrial equipment, non-slip surface
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Rolled original plate (2B)
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0.3 ~ 1.0
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Slightly bumpy, gray-white matte
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General purpose plate, sheet metal processing
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Pickling surface
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0.8 ~ 3.2
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Uniform grayish white, slightly rough
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Corrosion-resistant structural parts, pipes
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What is surface roughness?
Surface roughness refers to the degree of unevenness of the microscopic geometric shape of a material's surface, which is usually described by the height and spacing of the peaks and valleys on the surface. In professional terms, roughness is evaluated by measuring the fluctuation of the surface profile, and the unit is usually micrometers (μm). In the field of stainless steel, commonly used standards include Ra (Arithmetic Mean Roughness) and Rz (Maximum Height Roughness).
The importance of surface roughness of stainless steel
1. Affect the anti-corrosion performance
Stainless steel is widely used mainly due to its excellent corrosion resistance. However, this performance is closely related to its surface roughness. Higher surface roughness leads to more tiny grooves, which are prone to accumulate moisture, dirt and chemicals, thereby accelerating the corrosion process. On the contrary, a smooth surface is easier to clean and has stronger corrosion resistance.
2. Determine the appearance and aesthetic appeal
The appearance of stainless steel is of vital importance in architectural decoration or household items. Surface roughness directly affects its glossiness and texture. For instance, mirror-finished stainless steel requires extremely low roughness, while brushed stainless steel needs specific processes to form a uniform texture.
3. Enhance mechanical performance
In some industrial applications, the friction coefficient of the stainless steel surface is a key parameter, and the roughness will directly affect the friction performance. For instance, in food processing equipment, smooth stainless steel surfaces help reduce material residues and improve hygiene conditions.
4. Affect the adhesion of the coating
When coating or spraying treatment is required on the surface of stainless steel, surface roughness plays a crucial role. Appropriate roughness can enhance the adhesion of the coating, thereby improving the durability of the product.
The key factors affecting roughness
The material itself: Austenitic stainless steel (such as 304, 316) is easier to polish to a mirror finish, while martensitic stainless steel (such as 410) has a high hardness and is more difficult to polish.
Processing method:
Mechanical polishing: Through step-by-step grinding with a grinding wheel or polishing wheel, it can reach Ra 0.1 μm.
Electrolytic polishing: It achieves an ultra-smooth surface (Ra ≤0.05 μm) through electrochemical dissolution, while enhancing corrosion resistance.
Laser processing: It can precisely control local roughness (such as Ra 0.1 to 10 μm) and is used for functional surfaces.
Subsequent treatment: Passivation treatment can reduce the negative impact of roughness on corrosion resistance.
How to control the surface roughness of stainless steel?
1. Select the appropriate processing technology
The processing technology of stainless steel directly determines its surface roughness. For example:
Mechanical polishing: By using mechanical equipment to grind and polish stainless steel, a smooth surface can be achieved.
Electrolytic polishing: By using electrochemical methods to remove the tiny protrusions on the surface, a lower roughness is achieved.
- Brushing treatment: A uniform texture is formed on the surface of stainless steel through specific tools to meet decorative requirements.
2. Use high-precision measuring equipment
During the production process, the use of high-precision surface roughness measurement instruments (such as profilometers or laser scanners) can monitor and adjust processing parameters in real time to ensure that the products meet the expected roughness standards.
3. Optimize material selection
Different types of stainless steel respond differently to processing techniques. For instance, 304 stainless steel and 316 stainless steel may present different roughness after polishing. Therefore, it is also very important to select the appropriate stainless steel material according to the requirements.
4. Strengthen quality control
Establish a complete quality control system and conduct strict inspections on each batch of products to ensure that the surface roughness meets the design requirements. This can not only improve the product quality, but also reduce the production cost.
The Relationship between Roughness and performance
Corrosion resistance: The lower the roughness (Ra < 0.4 μm), the fewer the surface pores, and the stronger the resistance to pitting corrosion.
Cleanliness: Surfaces with Ra < 0.8 μm are easier to clean, meeting food/medical industry standards (such as FDA, GMP).
Bonding/Coating: A moderate roughness (Ra 1.6-3.2 μm) can enhance the adhesion of the coating.
Measurement Method
Contact measurement: Use a roughness meter (such as Taylor Hobson) to directly contact the surface, with high accuracy.
Non-contact measurement: Laser confocal microscope or white light interferometer, suitable for ultra-smooth surfaces (such as mirrors).
Comparison sample blocks: Quick comparison, but with relatively low accuracy.
Standard reference
ISO 1302: Specifies the symbol marking method for surface roughness.
ASTM A480: General Requirements for Surface Roughness of Stainless Steel Sheets.
Industry-specific standards: For instance, the semiconductor industry requires Ra < 0.05 μm, while architectural decoration might only need Ra < 1.6 μm.
Cases of surface roughness in practical applications
Case 1: Food processing equipment
The food industry has extremely high hygiene requirements. Stainless steel equipment needs a smooth and poreless surface to prevent bacterial growth. Therefore, such equipment usually adopts electrolytic polishing process to control the surface roughness below 0.8μm.
Case 2: Architectural Decoration
In high-end buildings, stainless steel curtain walls or elevator decorative panels are usually treated with mirror polishing to achieve a high-gloss effect, and their surface roughness is generally less than 0.1μm.
Case 3: Medical Devices
Medical devices have extremely high requirements for the cleanliness and corrosion resistance of material surfaces. Therefore, the roughness of stainless steel surfaces needs to be controlled within an extremely low range to ensure safety and durability.
