Quality Control Of ASTM F138 Stainless Steel Bars And Wires
Oct 27, 2026
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Why Quality Control Matters for ASTM F138 Stainless Steel
ASTM F138 stainless steel (UNS S31673) is a wrought 18Cr-14Ni-2.5Mo stainless steel specified for use in the manufacture of surgical implants. Because materials used in medical applications must meet clearly defined technical requirements, quality control is essential throughout material production, inspection, and delivery.
First, chemical composition directly affects the material's corrosion resistance and metallurgical characteristics. Chromium, nickel, and molybdenum contribute to the corrosion resistance of the stainless steel, while elements such as carbon, sulfur, and phosphorus must be controlled within the specified limits. Incorrect composition may affect material performance and consistency.
Second, mechanical properties must match the specified delivery condition. Tensile strength, yield strength, and elongation influence how the material behaves during machining, forming, and subsequent manufacturing processes. Annealed and cold-worked materials can exhibit significantly different strength and ductility, making it important to verify that test results correspond to the ordered condition.
Third, internal metallurgical quality cannot be confirmed by appearance alone. Nonmetallic inclusions and undesirable phases may not be visible on the material surface. Appropriate metallographic examinations and inclusion evaluations help verify compliance with the applicable requirements and provide additional evidence of material quality.
Finally, traceability is essential for verifying conformity. Chemical analysis, mechanical test results, and other inspection records should be linked to the relevant heat or material lot. This allows buyers to review the material's documented quality and confirm that the delivered products correspond to the agreed specifications.
For these reasons, quality control of ASTM F138 stainless steel bars and wires should not rely on a single test or material certificate. A systematic approach combining chemical analysis, mechanical testing, metallurgical evaluation, dimensional inspection, and traceable documentation provides a stronger basis for material acceptance in medical manufacturing.
Key Inspection Items for ASTM F138 Stainless Steel
Chemical Composition Verification
Chemical composition is the first step in verifying that stainless steel conforms to ASTM F138. Chromium, nickel, and molybdenum are important alloying elements, while carbon, sulfur, phosphorus, and other elements must remain within the specified limits.
The following table summarizes the heat-analysis requirements listed in ASTM F138-19.
Table 1. Chemical Composition Requirements (ASTM F138-19)
| Element | Requirement(wt.％) |
| C | ≤ 0.030 |
| Mn | ≤ 2.00 |
| P | ≤ 0.025 |
| S | ≤ 0.010 |
| Si | ≤ 0.75 |
| Cr | 17.00-19.00 |
| Ni | 13.00-15.00 |
| Mo | 2.25-3.00 |
| N | ≤ 0.10 |
| Cu | ≤ 0.50 |
| Co | ＜ 0.10 |
| Fe | Balance |
Note: The composition requirements and applicable notes must be checked against the exact edition of the standard used for the order.
In addition to the individual element limits, ASTM F138-19 specifies a minimum composition index:Cr + 3.3 × Mo ≥ 26.0
Chemical analysis may be performed using appropriate analytical equipment, such as optical emission spectrometry or other validated methods. The results should be compared with the specified limits, and the heat number should be linked to the relevant inspection records.
However, chemical composition is only one part of material qualification. A heat of steel that meets the chemical limits must still satisfy the applicable mechanical and metallurgical requirements.
Mechanical Property Testing
Mechanical testing evaluates whether the material has the required strength and ductility in its specified delivery condition. ASTM F138 includes tensile strength, yield strength, elongation, and Brinell hardness requirements, with the applicable values depending on product size and condition.
Table 2. Selected Mechanical Requirements in ASTM F138-19(Bar and Wire)
| Condition | Diameter or Thickness | Tensile Strength | Yield Strength | Elongation | Hardness |
| Hot worked | All sizes | -- | -- | -- | 250 HB |
| Annealed | ≥ 1.60 mm | 490 MPa | 190 MPa | 40 | -- |
| Cold worked | 1.60–38.1 mm | 860 MPa | 690 MPa | 12 | -- |
| Extra hard | 1.60–6.35 mm | 1,350 MPa | -- | -- | -- |
Fine Wire
| Condition | Diameter or Thickness | Tensile Strength | Elongation in 254mm, min, % |
|
Cold drawn
|
＜1.60 |
860 to 1035
|
5 |
Tensile strength indicates the maximum stress a material can withstand in a tensile test, while yield strength describes its ability to resist permanent deformation. Elongation reflects the material's ductility. Hardness testing is another method for evaluating a material's indentation response.
These values should not be interpreted out of context of the material's actual condition. For example, cold-worked materials may have higher strength than annealed materials, but their elongation may be lower. Therefore, delivery condition and mechanical property requirements should be agreed upon before production.
For medical applications, meeting strength test requirements does not alone prove that the material is suitable for a specific implant design. The manufacturer's design requirements and other applicable validation procedures remain crucial.
Metallographic Examination and Microcleanliness
Metallurgical quality is another important aspect of ASTM F138. Even when chemical composition and tensile properties meet the requirements, the internal structure of the steel must also be evaluated.
ASTM F138-19 specifies that the material must show no delta ferrite, chi phase, or sigma phase when examined metallographically at 100× magnification under the prescribed preparation and etching conditions.
The standard also establishes limits for nonmetallic inclusions, evaluated using the specified method and reference chart.
Table 3. Selected Microcleanliness Requirements in ASTM F138-19
| Inclusion Type | Thin-Series Maximum Rating | Heavy-Series Maximum Rating |
| Sulfides | 1.5 | 1.0 |
| Alumina | 1.5 | 1.0 |
| Silicates | 1.5 | 1.0 |
| Globular oxides | 1.5 | 1.0 |
Note: These are the maximum ratings specified in the referenced edition for the listed inclusion categories. The prescribed test method, specimen location, and evaluation procedure must be followed.
Nonmetallic inclusions are particles or compounds within the steel that differ from the surrounding metallic matrix. Their type, size, distribution, and quantity can affect material consistency and performance during subsequent processing.
Metallographic examination helps identify unwanted phases and assess the material's microstructure. Inclusion evaluation provides additional information about steel cleanliness. These examinations are particularly relevant when a buyer requires documented metallurgical quality for medical-grade material.
Grain size may also be important to a customer's material qualification or purchasing specification. However, it should not automatically be described as a mandatory acceptance criterion under ASTM F138 unless the applicable standard provisions or purchase order establish that requirement.
From Testing to Reliability: Understanding the Results
For ASTM F138 stainless steel bars and wires, quality assessment requires more than checking individual test results. Each inspection method evaluates a different aspect of material quality.
For example, chemical analysis verifies alloy composition, while tensile testing evaluates strength and ductility. Neither test replaces metallographic examination, which helps assess microstructure and nonmetallic inclusions according to the applicable requirements. Traceability is equally important. Test reports and material certificates should be linked to the corresponding heat or material lot to ensure that the inspection results apply to the products delivered.
Therefore, reliable quality control depends on three key factors: compliance with all applicable requirements, appropriate inspection methods, and traceable documentation.
Traceability and Quality Documentation
For ASTM F138 stainless steel bars and wires, traceability is an important part of quality assurance. Inspection results are meaningful only when they can be linked to the actual material supplied. Clear identification and complete documentation help buyers verify material conformity and maintain quality records throughout the manufacturing process.
Depending on the purchase order and inspection requirements, relevant documentation may include:
Material Test Certificate (MTC): Records chemical composition and applicable mechanical test results.
Heat Number and Lot Identification: Connects the supplied material with its production and inspection records.
Metallographic Inspection Reports: Provide supporting evidence of microstructure and inclusion evaluation when required.
Dimensional and Surface Inspection Records: Confirm compliance with the agreed dimensions, tolerances, and surface requirements.
Processing and Heat Treatment Records: Provide additional process information when specified by the purchaser.
Before shipment, the supplier should ensure that material markings, certificates, and inspection reports are consistent with the delivered product. Any additional testing or documentation requirements should be agreed upon before production.
A well-organized traceability system helps reduce documentation discrepancies, simplifies incoming material verification, and provides buyers with greater confidence in the consistency of ASTM F138 stainless steel bars and wires.
What Should Buyers Consider When Selecting an ASTM F138 Supplier?
Selecting an ASTM F138 stainless steel supplier involves more than comparing prices. Buyers should consider material conformity, inspection capabilities, dimensional accuracy, and documentation to ensure that the supplied products meet their technical requirements.
First, confirm the material specifications. Product form, dimensions, tolerances, delivery condition, surface finish, and the applicable ASTM F138 edition should be clearly defined before ordering.
Second, evaluate quality management and inspection capabilities. Relevant management system certifications can provide additional information about a supplier's approach to quality control, process management, and product traceability. For medical-related material supply, ISO 13485 is particularly relevant because it addresses quality management systems for medical devices. AS9100D also demonstrates a quality management framework designed for the aerospace industry.
Our company holds certifications including ISO 9001, ISO 28000, ISO 45001, AS9100D, ISO 13485, and CE-related certification. These certifications reflect different aspects of our management and compliance framework, covering areas such as quality management, supply chain security, occupational health and safety, medical-device quality management, and applicable product conformity requirements.
Finally, verify the material documentation. Buyers should confirm that material test certificates, chemical analysis, mechanical test results, and other required inspection records correspond to the supplied heat or lot. Additional requirements, such as metallographic examination or specific grain-size limits, should be agreed upon before production.
By combining relevant management systems with clearly defined product specifications and traceable inspection records, we aim to support customers seeking reliable ASTM F138 stainless steel bars and wires for medical manufacturing applications. Buyers are welcome to contact our team to discuss dimensions, delivery conditions, testing requirements, and documentation needs.
For details regarding our certifications, please visit our official website – About Us – for more information.https://www.lorkalloy.com/certification
If needed, you can also view our medical-grade stainless steel rods/wires that meet ASTM F138 standards. Click the image or blue link to go there.
ASTM F138 316LVM Medical Grade Stainless Steel Bars/Wires
We are available at any time to provide quotes and dimensional information-please feel free to contact us.
Lork Group
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📧 layla@lorkgroup.com | 📞 +86 199 3707 5488
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