ASTM A193 – Mechanical & Material Properties
The ASTM A193 / A193M specification covers alloy and stainless steel bolting for pressure vessels, valves, flanges, and fittings intended for high-temperature or high-pressure service. This standard is a technical benchmark in industries requiring high-performance fasteners, categorizing materials primarily into ferritic steels and austenitic stainless steels (such as grades B5, B7, B8, and B16). The practical application guide is:
- Unit Systems: The specification is expressed in both inch-pound and SI units. Unless the purchase order specifies the "M" designation, inch-pound units shall apply by default.
- Heat Treatment Classes: For austenitic stainless steels, purchasers must specify the heat-treated condition, such as Class 1 (carbide solution treated), Class 1A (solution treated in the finished condition), or Class 2 (solution treated and strain-hardened).
- Mandatory General Requirements: All bolting must conform to ASTM A962/A962M. These requirements include essential standards for test methods, finish, thread dimensions, and certification.
- Coatings: Coatings are prohibited unless specifically ordered. If coatings are used, application limits are critical: zinc-coated fasteners should be limited to temperatures below 390°F [210°C], and cadmium-coated fasteners below 300°F [160°C] to prevent embrittlement.
- Product Marking: Each fastener must be marked with a specific grade symbol (e.g., B7, B8) and the manufacturer's identification. Notably, Grade B7M requires a line under the marking symbol to indicate it has been 100% evaluated for hardness.
Mechanical Properties
Under the ASTM A193 / A193M specification, all bolting materials must conform to strict mechanical requirements, including tensile strength, yield strength, elongation, and reduction of area. These properties are determined at room temperature after the specified heat treatment has been completed. For professionals applying this standard, it is important to note that while tension specimen tests are standard, Class 2, 2B, and 2C strain-hardened fasteners may be tested full-size, with those results taking precedence in the event of a conflict. The key compliance factors are as follows :
- Hardness Testing: Each grade has defined maximum hardness limits to ensure material integrity; notably, Grade B7M requires a minimum hardness of 200 HB and a maximum of 235 HB.
- Section Size Uniformity: For austenitic steels in the strain-hardened condition (Class 2), properties may not be uniform throughout the cross-section, particularly for fasteners with diameters exceeding 3/4 inch [M20].
- Specimen Location: For large-diameter bolting (1-1/2 inches [M38] and over), properties at the center or core may be lower than those reported from tests taken at the standard 1/2 radius location.
- Wedge Tensile Testing: Headed fasteners with a body diameter of 1-1/2 inches or smaller must undergo full-size wedge tensile testing to confirm the strength of the head-to-shank junction.
The tables below detail the specific mechanical requirements for both inch-pound and metric fasteners across all ferritic and austenitic grades.
| Mechanical Properties For Inch Fasteners | ||||||
|---|---|---|---|---|---|---|
| Grade | Thread Size (inch) | Tensile Strength, min (ksi) | Yield Strength 0.2% offset, min (ksi) | Elongation in 4D, min (%) | Reduction of Area, min (%) | Hardness, max |
| B5 | up to 4 inch | 100 | 80 | 16 | 50 | - |
| B6 | up to 4 inch | 110 | 85 | 15 | 50 | - |
| B6X | up to 4 inch | 90 | 70 | 16 | 50 | 26 HRC |
| B7 | 2-1/2 and under | 125 | 105 | 16 | 50 | 321 HB or 35 HRC |
| over 2-1/2 to 4 | 115 | 95 | 16 | 50 | 321 HB or 35 HRC | |
| over 4 to 7 | 100 | 75 | 18 | 50 | 321 HB or 35 HRC | |
| B7M | 4 and under | 100 | 80 | 18 | 50 | 235 HB or 99 HRB |
| over 4 to 7 | 100 | 75 | 18 | 50 | 235 HB or 99 HRB | |
| B16 | 2-1/2 and under | 125 | 105 | 18 | 50 | 321 HB or 35 HRC |
| over 2-1/2 to 4 | 110 | 95 | 17 | 45 | 321 HB or 35 HRC | |
| over 4 to 8 | 100 | 85 | 16 | 45 | 321 HB or 35 HRC | |
| B8, B8M, B8P, B8LN, B8MLN (Class 1) | all diameters | 75 | 30 | 30 | 50 | 223 HB or 96 HRB |
| B8C, B8T (Class 1) | all diameters | 75 | 30 | 30 | 50 | 223 HB or 96 HRB |
| B8A, B8CA, B8MA, B8PA, B8TA, B8LNA, B8MLNA, B8NA, B8MNA, B8MLCuNA (Class 1A) | all diameters | 75 | 30 | 30 | 50 | 192 HB or 90 HRB |
| B8N, B8MN, B8MLCuN (Class 1B) | all diameters | 80 | 35 | 30 | 40 | 223 HB or 96 HRB |
| B8R (Class 1C) | all diameters | 100 | 55 | 35 | 55 | 271 HB or 28 HRC |
| B8RA (Class 1C) | all diameters | 100 | 55 | 35 | 55 | 271 HB or 28 HRC |
| B8S (Class 1C) | all diameters | 95 | 50 | 35 | 55 | 271 HB or 28 HRC |
| B8SA (Class 1C) | all diameters | 95 | 50 | 35 | 55 | 271 HB or 28 HRC |
| B8, B8C, B8P, B8T, B8N (Class 2) | 3/4 and under | 125 | 100 | 12 | 35 | 321 HB or 35 HRC |
| over 3/4 to 1, incl | 115 | 80 | 15 | 35 | 321 HB or 35 HRC | |
| over 1 to 1-1/4, incl | 105 | 65 | 20 | 35 | 321 HB or 35 HRC | |
| over 1-1/4 to 1-1/2, incl | 100 | 50 | 28 | 45 | 321 HB or 35 HRC | |
| B8M, B8MN, B8MLCuN (Class 2) | 3/4 and under | 110 | 95 | 15 | 45 | 321 HB or 35 HRC |
| over 3/4 to 1, incl | 100 | 80 | 20 | 45 | 321 HB or 35 HRC | |
| over 1 to 1-1/4, incl | 95 | 65 | 25 | 45 | 321 HB or 35 HRC | |
| over 1-1/4 to 1-1/2, incl | 90 | 50 | 30 | 45 | 321 HB or 35 HRC | |
| B8, B8M2 (Class 2B) | 2 and under | 95 | 75 | 25 | 40 | 321 HB or 35 HRC |
| over 2 to 2-1/2, incl | 90 | 65 | 30 | 40 | 321 HB or 35 HRC | |
| over 2-1/2 to 3, incl | 80 | 55 | 30 | 40 | 321 HB or 35 HRC | |
| B8M3 (Class 2C) | 2 and under | 85 | 65 | 30 | 60 | 321 HB or 35 HRC |
| over 2 | 85 | 60 | 30 | 60 | 321 HB or 35 HRC | |
| Mechanical Properties For Metric Fasteners | ||||||
|---|---|---|---|---|---|---|
| Grade | Thread Size (mm) | Tensile Strength, min (MPa) | Yield Strength 0.2% offset, min (MPa) | Elongation in 4D, min (%) | Reduction of Area, min (%) | Hardness, max |
| B5 | up to M100, incl | 690 | 550 | 16 | 50 | - |
| B6 | up to M100, incl | 760 | 585 | 15 | 50 | - |
| B6X | up to M100, incl | 620 | 485 | 16 | 50 | 26 HRC |
| B7 | M64 and under | 860 | 720 | 16 | 50 | 321 HB or 35 HRC |
| over M64 to M100 | 795 | 655 | 16 | 50 | 321 HB or 35 HRC | |
| over M100 to M180 | 690 | 515 | 18 | 50 | 321 HB or 35 HRC | |
| B7M | M100 and under | 690 | 550 | 18 | 50 | 235 HB or 99 HRB |
| over M100 to M180 | 690 | 515 | 18 | 50 | 235 HB or 99 HRB | |
| B16 | M64 and under | 860 | 725 | 18 | 50 | 321 HB or 35 HRC |
| over M64 to M100 | 760 | 655 | 17 | 45 | 321 HB or 35 HRC | |
| over M100 to M180 | 690 | 585 | 16 | 45 | 321 HB or 35 HRC | |
| Class 1 and 1D: B8, B8M, B8P, B8LN, B8MLN | all diameters | 515 | 205 | 30 | 50 | 223 HB or 96 HRB |
| Class 1: B8C, B8T | all diameters | 515 | 205 | 30 | 50 | 223 HB or 96 HRB |
| Class 1A: B8A, B8CA, B8MA, B8PA, B8TA, B8LNA, B8MLNA, B8NA, B8MNA, B8MLCuNA | all diameters | 515 | 205 | 30 | 50 | 192 HB or 90 HRB |
| Class 1B and 1D: B8N, B8MN, B8MLCuN | all diameters | 550 | 240 | 30 | 40 | 223 HB or 96 HRB |
| Class 1C and 1D: B8R | all diameters | 690 | 380 | 35 | 55 | 271 HB or 28 HRC |
| Class 1C: B8RA | all diameters | 690 | 380 | 35 | 55 | 271 HB or 28 HRC |
| Class 1C and 1D: B8S | all diameters | 655 | 345 | 35 | 55 | 271 HB or 28 HRC |
| Class 1C: B8SA | all diameters | 655 | 345 | 35 | 55 | 271 HB or 28 HRC |
| Class 2: B8, B8C, B8P, B8T, B8N | M20 and under | 860 | 690 | 12 | 35 | 321 HB or 35 HRC |
| over M20 to M24, incl | 795 | 550 | 15 | 35 | 321 HB or 35 HRC | |
| over M24 to M30, incl | 725 | 450 | 20 | 35 | 321 HB or 35 HRC | |
| over M30 to M36, incl | 690 | 345 | 28 | 45 | 321 HB or 35 HRC | |
| Class 2: B8M, B8MN, B8MLCuN | M20 and under | 760 | 655 | 15 | 45 | 321 HB or 35 HRC |
| over M20 to M24, incl | 690 | 550 | 20 | 45 | 321 HB or 35 HRC | |
| over M24 to M30, incl | 655 | 450 | 25 | 45 | 321 HB or 35 HRC | |
| over M30 to M36, incl | 620 | 345 | 30 | 45 | 321 HB or 35 HRC | |
| Class 2B: B8, B8M2 | M48 and under | 655 | 515 | 25 | 40 | 321 HB or 35 HRC |
| over M48 to M64, incl | 620 | 450 | 30 | 40 | 321 HB or 35 HRC | |
| over M64 to M72, incl | 550 | 380 | 30 | 40 | 321 HB or 35 HRC | |
| Class 2C: B8M3 | M48 and under | 585 | 450 | 30 | 60 | 321 HB or 35 HRC |
| over M48 | 585 | 415 | 30 | 60 | 321 HB or 35 HRC | |
Material Properties
The Material Properties section of ASTM A193 / A193M outlines the precise chemical requirements for each grade of alloy and stainless steel bolting. Compliance with these chemical compositions is mandatory to ensure the fasteners perform reliably under the specific high-temperature or high-pressure conditions for which they were designed. The technical compliance and requirements are as follow :
- Grade Selection: Selection of a specific grade depends on the required mechanical properties, design parameters, and high-temperature service environment.
- Heat Analysis: A chemical analysis of each heat of steel must be performed by the manufacturer to verify that the percentages of specified elements fall within the required ranges.
- Prohibited Elements: To maintain material integrity, the intentional addition of bismuth (Bi), selenium (Se), tellurium (Te), and lead (Pb) is strictly prohibited.
- Reporting Requirements: Any element present in a concentration greater than 0.75 weight % must be reported in the certification.
- Consistency: While individual product analyses may vary slightly from specified limits, multiple determinations of a single element within a heat cannot vary both above and below the specified range.
The table below provides the detailed chemical composition requirements for the ferritic and austenitic stainless steel grades covered by this specification.
| Chemical Composition | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Grade | Uns Designation | Carbon, (%) | Manganese, (%) | Phosphorus, (%) | Sulfur, (%) | Silicon, (%) | Chromium, (%) | Nickel, (%) | Molybdenum, (%) | Vanadium, (%) | Aluminum, (%) | Columbium + Tantalum, (%) | Titanium, (%) | Nitrogen, (%) | Copper, (%) |
| B5 | - | 0.10 (min) | 1.00 (max) | 0.040 (max) | 0.030 (max) | 1.00 (max) | 4.0 - 6.0 | - | 0.40 - 0.65 | - | - | - | - | - | - |
| B6 and B6X | S41000 (410) | 0.08 - 0.15 | 1.00 (max) | 0.040 (max) | 0.030 (max) | 1.00 (max) | 11.5 - 13.5 | - | - | - | - | - | - | - | - |
| B7 and B7M | - | 0.37 - 0.49 | 0.65 - 1.10 | 0.035 (max) | 0.040 (max) | 0.15 - 0.35 | 0.75 - 1.20 | - | 0.15 - 0.25 | - | - | - | - | - | - |
| B16 | - | 0.36 - 0.47 | 0.45 - 0.70 | 0.035 (max) | 0.040 (max) | 0.15 - 0.35 | 0.80 - 1.15 | - | 0.50 - 0.65 | 0.25 - 0.35 | 0.015 (max) | - | - | - | - |
| B8 and B8A | S30400 (304) | 0.08 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 18.0 - 20.0 | 8.0 - 11.0 | - | - | - | - | - | - | - |
| B8C and B8CA | S34700 (347) | 0.08 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 17.0 - 19.0 | 9.0 - 12.0 | - | - | - | (10 x Carbon (min)) - 1.10 (max) | - | - | - |
| B8M, B8MA, B8M2, B8M3 | S31600 (316) | 0.08 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 16.0 - 18.0 | 10.0 - 14.0 | 2.00 - 3.00 | - | - | - | - | - | - |
| B8P and B8PA | S30500 | 0.12 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 17.0 - 19.0 | 11.0 - 13.0 | - | - | - | - | - | - | - |
| B8N and B8NA | S30451 (304N) | 0.08 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 18.0 - 20.0 | 8.0 - 11.0 | - | - | - | - | - | 0.10 - 0.16 | - |
| B8MN and B8MNA | S31651 (316N) | 0.08 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 16.0 - 18.0 | 10.0 - 13.0 | 2.00 - 3.00 | - | - | - | - | 0.10 - 0.16 | - |
| B8MLCuN and B8MLCuNA | S31254 | 0.020 (max) | 1.00 (max) | 0.030 (max) | 0.010 (max) | 0.80 (max) | 19.5 - 20.5 | 17.5 - 18.5 | 6.00 - 6.50 | - | - | - | - | 0.18 - 0.22 | 0.50 - 1.00 |
| B8T and B8TA | S32100 (321) | 0.08 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 17.0 - 19.0 | 9.0 - 12.0 | - | - | - | - | (5 x (Carbon + Nitrogen) (min)) - 0.70 (max) | - | - |
| B8R and B8RA | S20910 | 0.06 (max) | 4.0 - 6.0 | 0.045 (max) | 0.030 (max) | 1.00 (max) | 20.5 - 23.5 | 11.5 - 13.5 | 1.50 - 3.00 | 0.10 - 0.30 | - | 0.10 - 0.30 | - | 0.20 - 0.40 | - |
| B8S and B8SA | S21800 | 0.10 (max) | 7.0 - 9.0 | 0.060 (max) | 0.030 (max) | 3.5 - 4.5 | 16.0 - 18.0 | 8.0 - 9.0 | - | - | - | - | - | 0.08 - 0.18 | - |
| B8LN and B8LNA | S30453 | 0.030 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 18.0 - 20.0 | 8.0 - 11.0 | - | - | - | - | - | 0.10 - 0.16 | - |
| B8MLN and B8MLNA | S31653 | 0.030 (max) | 2.00 (max) | 0.045 (max) | 0.030 (max) | 1.00 (max) | 16.0 - 18.0 | 10.0 - 13.0 | 2.00 - 3.00 | - | - | - | - | 0.10 - 0.16 | - |