ASTM A193 Grade B7 Specification

High Temperature High Pressure Bolting Material

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