ASTM A193 Grade B7 Specification
ASTM A193 Grade B7 specification covers requirements for high tensile alloy steel bolting material for use in high temperature or high-pressure service and other special purpose applications. It is a standard specification defining typical chemical composition, mechanical properties, hardness requirement, preferential heat treatment, product marking, certification and other requirements, suitable for bolting used in pressure vessel service, valves, flanges and fittings. ASTM A193 defines both SI (Metric) and inch-pound units.
Grade B7 is a heat-treated chromium-molybdenum low-alloy steel with minimum tensile strength requirement of 125 ksi (860 Mpa), yield 105 ksi (720 Mpa), and maximum hardness of 35HRC. Boltport uses Alloy Steel AISI 4140 bar stock or forging stock to produce B7 headed and non-headed bolts. A193 Grade B7 is the most commonly used Bolt specification coupled with A194 Grade 2H Nuts for Bolting Carbon Steel pipeline. A193 B7 bolting is available in metric sizes from M6 to M180 and imperial sizes from 1/4 to 7 inches, in diameter.
Find information on ASTM A193 Grade B7 chemical composition, mechanical properties such as tensile strength; yield strength, hardness, marking requirements and reference product standards.
ASTM A193 Grade B7 Chemical Composition
| Elements | Range | Product Variation, Over or Under B |
| Carbon | 0.37-0.49 % D | 0.02 % |
| Manganese, max | 0.65-1.10 % | 0.04 % |
| Phosphorus, max | 0.035 % | 0.005 % over |
| Sulfur, max | 0.040 % | 0.005 % over |
| Silicon | 0.15 - 0.35 % | 0.02 % |
| Chromium | 0.75-1.20 % | 0.05 % |
| Molybdenum | 0.15-0.25 % | 0.02 % |
B Product analysis - Individual determinations sometimes vary from the specified limits on ranges as shown in the tables. The several determinations of any individual element in a heat may not vary both above and below the specified range.
D For bar sizes over 31/2 in. [90 mm], inclusive, the carbon content may be 0.50 %, max. For the B7M grade, a minimum carbon content of 0.28 % is permitted, provided that the required tensile properties are met in the section sizes involved; the use of AISI 4130 or 4130H is allowed.
Heat Treatment
B7 and B7M shall be heat treated by quenching in a liquid medium and tempering. For B7M fasteners, the final heat treatment, which may be the tempering operation if conducted at 1150 °F [620 °C] minimum, shall be done after all machining and forming operations, including thread rolling and any type of cutting. Surface preparation for hardness testing, nondestructive evaluation, or ultrasonic bolt tensioning is permitted.
Unless otherwise specified, material for Grade B7 may be heat-treated by the Furnace, the Induction or the Electrical Resistance method.
ASTM A193 Grade B7 Mechanical Properties - Metric Sizes
| Diameter mm | Min Tempering Temperature, °C | Tensile Strength min, MPa | Yield strength, min, 0.2% offset, MPa | Elongation in 4D min, % | Reduction of Area, min, % | Hardness, max |
| M64 and Under | 593 | 860 | 720 | 16 | 50 | 321 HBW or 35 HRC |
| over M64 to M100 | 593 | 795 | 655 | 16 | 50 | 321 HBW or 35 HRC |
| over M100 to M180 | 593 | 690 | 515 | 18 | 50 | 321 HBW or 35 HRC |
ASTM A193 Grade B7 Mechanical Properties - Inch Sizes
| Diameter Inch | Min Tempering Temperature, °C | Tensile Strength min, ksi | Yield strength, min, 0.2% offset, ksi | Elongation in 4D min, % | Reduction of Area, min, % | Hardness, max |
| 2.5 and under | 1100 | 125 | 105 | 16 | 50 | 321 HBW or 35 HRC |
| over 2.5 to 4 | 1100 | 115 | 95 | 16 | 50 | 321 HBW or 35 HRC |
| over 4 to 7 | 1100 | 100 | 75 | 18 | 50 | 321 HBW or 35 HRC |
ASTM A193 Grade B7 Bolt Marking
| BPF B7 | "BPF" Manufacturer's Logo & "B7" Grade Marking |
Recommended Hardware
| Nuts | Washers |
|---|---|
| ASTM A194 Grade 2H | Mild Steel / Carbon Steel |
Reference Standards
- ASTM A153/A153M : Specification for Zinc Coating Hot Dip Galvanizing on Fasteners.
- ASTM A194/A194M : Specification for Carbon and Alloy Steel Nuts for ASTM A193 Bolts.
- ASTM A320/A320M : Specification for alloy-steel and stainless steel bolting for low temperature service.
- ASME B18.2.1 : Square and Hex Bolts and Screws.
- ASME B18.2.3.3M : Metric Heavy Hex Screws
- ASME B18.3 : Hexagon Socket and Spline Socket Screws
- ASME B18.3.1M : Metric Socket Head Cap Screws
ASTM A193 Grade B7 specification is a comprehensive standard governing high tensile alloy steel bolting material, primarily used in high-pressure or high-temperature applications. This specification encompasses a range of critical factors, including chemical composition, mechanical properties, heat treatment, product marking, and certifications. The grade defines the characteristics required for bolts used in pressure vessels, valves, flanges, and fittings.
Let's break down the key aspects:
Chemical Composition:
- Carbon: Ranges between 0.37-0.49%. Deviations allowed within 0.02%.
- Manganese: Maximum limit of 0.65-1.10%, with a deviation tolerance of 0.04%.
- Phosphorus & Sulfur: Maximum limits specified with slight overages allowed.
- Silicon, Chromium, Molybdenum: Specific ranges provided with slight deviations permitted.
- Note: For larger bar sizes over 3.5 inches, carbon content may vary up to 0.50% max. Additionally, for B7M grade, a minimum carbon content of 0.28% is permitted if the required tensile properties are met.
Heat Treatment:
- B7 and B7M undergo quenching in a liquid medium followed by tempering. Specific temperature ranges and final heat treatment conditions are outlined.
Mechanical Properties:
- Tensile Strength: Minimum of 125 ksi (860 MPa).
- Yield Strength: Minimum of 105 ksi (720 MPa).
- Hardness: Maximum of 35 HRC.
- Elongation & Reduction of Area: Specifications for different diameter ranges are provided for both metric and inch sizes.
Bolt Marking:
- Manufacturer's logo "BPF" and "B7" grade marking are recommended for identification.
Recommended Hardware:
- Nuts: ASTM A194 Grade 2H.
- Washers: Mild Steel / Carbon Steel.
Reference Standards:
- ASTM A153/A153M: Zinc Coating Hot Dip Galvanizing on Fasteners.
- ASTM A194/A194M: Carbon and Alloy Steel Nuts for ASTM A193 Bolts.
- ASTM A320/A320M: Alloy-steel and Stainless Steel Bolting for Low Temperature Service.
- ASME B18.2.1, B18.2.3.3M, B18.3, B18.3.1M: Specifications for different types of bolts, screws, and fasteners.
The Grade B7 specification offers detailed guidelines ensuring the reliability and performance of high tensile alloy steel bolting materials across various industrial applications, providing specific tolerances, treatments, and quality standards for manufacturing and usage.
