SMT and stainless steel surface quality
Stainless steel is widely used in applications with specific requirements for material performance and surface quality. Beyond the properties of the alloy itself, surface roughness, microscopic surface texture and cleanliness may influence cleanability, corrosion resistance and performance in service.
After earlier manufacturing operations, stainless steel components may retain machining marks, microscopic irregularities and uneven surface features. These characteristics affect surface roughness and may also create locations where moisture, contaminants or corrosive substances can accumulate.
Stainless Steel Micro Treatment (SMT) is KUN-QI's core stainless steel surface treatment technology. It focuses on refining the microscopic surface condition, reducing surface roughness and helping to improve surface quality and corrosion performance.
KUN-QI can treat stainless steel components to achieve the customer-specified target Ra value or a lower surface roughness value. As materials, component geometries and initial surface conditions differ, the required treatment conditions and processing times must be assessed individually.
This article explains SMT, its relationship with Ra surface roughness, its potential benefits for corrosion resistance and the considerations involved in specifying surface treatment.
1. What Is Stainless Steel Micro Treatment?
SMT stands for Stainless Steel Micro Treatment.
It is a specialist stainless steel surface treatment technology offered by KUN-QI for customer-supplied components. Treatment conditions are planned according to the material, initial surface condition, specified roughness and surface quality requirements.
SMT focuses on improving the microscopic surface condition rather than machining, forming or manufacturing the components themselves.
SMT is applied to the entire component and is not offered as a selective treatment of designated local areas.
The treatment can refine the original surface condition, reduce roughness and support the required surface quality.
For components with specified Ra requirements, the treatment can be planned around the target value and verified using appropriate measurement methods.
SMT is the technology name used by KUN-QI and is not a universally defined ISO, ASTM or SAE standard process.
2. How Does SMT Relate to Ra Surface Roughness?
Ra is a commonly used surface roughness parameter. It represents the arithmetic mean of the absolute profile height deviations under the applicable measurement and evaluation conditions.
Typical requirements include:
- Ra 0.8 μm
- Ra 0.4 μm
- Ra 0.2 μm
- Other Ra values specified for particular applications
Under comparable measurement conditions, a lower Ra generally indicates smaller average height variations in the measured surface profile.
KUN-QI's SMT technology can achieve the customer-specified target Ra value or a lower surface roughness value.
For example, if a customer specifies Ra 0.4 μm, the treatment objective is to meet Ra 0.4 μm or a lower roughness value. If Ra 0.2 μm is required, suitable treatment conditions are assessed against that target.
However, materials, component geometries, initial surface conditions and treatment requirements vary. Treatment conditions and processing times must therefore be assessed for each component.
The same Ra target does not necessarily mean the same treatment difficulty, time or cost.
3. How Does SMT Improve Microscopic Surface Quality?
Before surface treatment, stainless steel components may have machining marks, microscopic peaks and valleys, surface irregularities or uneven features.
These characteristics influence roughness and may make it easier for contaminants, moisture and other substances to remain in certain surface areas.
SMT focuses on refining microscopic surface texture, reducing specified roughness and improving the consistency of surface quality.
Relevant considerations include:
- Initial surface roughness.
- Existing surface marks and microscopic condition.
- Stainless steel grade and material condition.
- Component dimensions and geometry.
- Suitability for whole-component surface treatment.
- Target Ra value.
- Surface quality and acceptance criteria.
- Required treatment time.
With suitable treatment, a refined microscopic surface may reduce certain features that retain contaminants and support improved cleanability and corrosion performance.
However, Ra is only one surface texture parameter. It does not fully describe scratches, isolated defects, surface directionality or every microscopic surface feature.
Additional acceptance requirements may therefore be necessary for specific applications.
4. How Does SMT Compare with Mechanical Polishing and Electropolishing?
Stainless steel surface treatment includes different technologies with distinct principles, characteristics and application requirements.
Stainless Steel Micro Treatment (SMT)
SMT is KUN-QI's core stainless steel micro-surface treatment technology.
It focuses on meeting customer-specified Ra values and surface quality requirements through whole-component treatment planning.
The actual treatment method and suitability are determined using KUN-QI's technical information and individual assessment.
Mechanical Polishing
Mechanical polishing modifies a metal surface through abrasive and mechanical action.
The outcome depends on the abrasives, treatment conditions, original surface and material characteristics. Directional polishing marks may remain.
Electropolishing
Electropolishing improves metal surface condition through controlled electrochemical material removal.
The result depends on the material, initial surface condition, component geometry and process parameters. The same degree of roughness improvement cannot be assumed for every component.
Comparison of Surface Treatment Technologies
| Method | Main focus | Key considerations |
|---|---|---|
| SMT | KUN-QI whole-component stainless steel micro-surface treatment | Specified Ra, microscopic surface quality, treatment conditions and time |
| Mechanical polishing | Abrasive and mechanical surface modification | Surface marks, abrasives, initial condition and treatment parameters |
| Electropolishing | Electrochemical surface treatment | Material, surface condition, geometry and process parameters |
Different technologies may suit different applications and may sometimes be used in combination.
The choice should be based on the product's roughness, surface quality and other technical requirements rather than the treatment name alone.
5. Why Does Treatment Time Vary for the Same Ra Requirement?
Even when two stainless steel components have the same Ra target, the required surface treatment time may differ.
Initial Surface Condition
Existing roughness, surface marks and irregularities may affect the treatment required to achieve the specified Ra.
Component Geometry
Flat surfaces, curves, recesses, holes and complex structures may present different whole-component treatment requirements.
Stainless Steel Grade
Different stainless steel grades and material conditions may influence treatment planning.
Component Size and Overall Surface Condition
Component dimensions, overall structure and initial surface condition may affect treatment requirements and time.
Surface Quality and Acceptance Requirements
Additional requirements relating to appearance, local defects, dimensional preservation or other acceptance criteria may increase treatment and inspection time.
KUN-QI's SMT technology can achieve the specified Ra value or a lower roughness value, but treatment conditions and processing times must be assessed individually.
For this reason, surface treatment quotations should be based on the actual component requirements rather than the Ra value alone.
6. How Can SMT Improve Stainless Steel Corrosion Resistance by Reducing Surface Roughness?
The microscopic surface condition of stainless steel is closely related to its corrosion performance.
Pronounced microscopic irregularities, machining marks and uneven surface features may retain moisture, contaminants or corrosive substances, increasing the risk of localised corrosion.
By reducing surface roughness to the customer-specified Ra requirement, SMT can refine the microscopic surface condition and reduce certain features that may retain contaminants and corrosive media.
SMT can therefore improve stainless steel surface roughness while also helping to enhance cleanability and corrosion resistance.
Where material, contamination and service conditions are otherwise comparable, lower surface roughness generally helps reduce some forms of contaminant retention and may improve corrosion performance.
Actual corrosion resistance also depends on stainless steel grade, surface contamination, passive condition and service environment.
The corrosion benefits of SMT should therefore be evaluated in relation to the material and application. Specific corrosion performance requirements should be verified using appropriate tests.
7. Which Stainless Steel Components May Be Suitable for SMT?
SMT can be assessed for stainless steel components with specified surface roughness, microscopic surface quality, cleanliness or corrosion-related requirements.
Examples include:
- Stainless steel components with defined Ra specifications.
- Parts requiring lower initial surface roughness.
- Components requiring refinement of microscopic surface characteristics.
- Products with specific surface cleanliness requirements.
- Components suitable for whole-component surface treatment.
- Single-piece prototypes and development samples.
- Low-volume, varied surface treatment requirements.
- Components requiring surface acceptance based on engineering drawings.
KUN-QI specialises in professional surface treatment of customer-supplied stainless steel components.
Suitability depends on the material, geometry, initial surface condition and specified treatment requirements.
8. What Information Is Needed Before SMT Surface Treatment?
Customers are encouraged to provide:
- Stainless steel grade.
- Component drawings or dimensions.
- Initial surface condition.
- Target Ra value and units.
- Overall component structure and surface treatment requirements.
- Quantity.
- Surface quality and acceptance requirements.
- Specific cleanliness, corrosion resistance or service environment requirements.
SMT is applied to the entire component rather than selected local areas, so customers do not need to specify individual treatment zones.
Where a complete surface treatment specification is not yet available, existing product information can be used to discuss the technical requirements and feasibility.
For products with specific corrosion resistance requirements, the relevant testing conditions and acceptance criteria should also be provided.
9. How Are Ra and Surface Quality Verified After SMT?
After SMT surface treatment, roughness should be verified according to the specified measurement method, engineering requirements and acceptance criteria.
Relevant considerations include:
- Contact or non-contact measurement methods.
- Measurement location and direction.
- Profile filtering and evaluation conditions.
- Instrument suitability.
- Component geometry.
- Measurement uncertainty.
The ISO 21920 series provides relevant references for profile surface texture specifications.
An Ra measurement confirms surface roughness; it is not a corrosion resistance test.
Where specific corrosion resistance is required, the applicable test methods and acceptance criteria should be agreed separately.
ISO 21920 does not certify SMT as a surface treatment process.
10. KUN-QI Professional SMT Stainless Steel Surface Treatment Services
KUN-QI specialises in stainless steel surface treatment, with Stainless Steel Micro Treatment (SMT) as its core technology.
SMT focuses on refining microscopic surface condition, reducing surface roughness and helping to improve cleanability and corrosion performance.
KUN-QI's SMT technology can achieve the customer-specified target Ra value or a lower surface roughness value.
For customer-supplied components, treatment conditions are assessed according to the material, initial surface condition, target Ra, surface quality and other technical requirements.
Because components differ in material, geometry and initial surface condition, the required treatment conditions and processing times may vary.
KUN-QI provides stainless steel surface treatment for single-piece prototypes, low-volume orders and varied customer requirements, serving B2B customers with defined surface quality specifications.
Customers are welcome to submit drawings, material information, target Ra values, quantities and acceptance requirements through KUN-QI's official website to discuss SMT surface treatment.
Technical References
- ISO 21920-1 — Surface texture: Profile — Indication of surface texture
- ISO 21920-2 — Surface texture: Profile — Terms, definitions and surface texture parameters
- ISO 21920-3 — Surface texture: Profile — Specification operators
Technical note: SMT is the technology name used by KUN-QI. These ISO standards address surface texture specifications and do not constitute certification of the SMT process or KUN-QI's surface treatment capabilities.