ASTM A193 Grade B7 Heavy Hex Bolts | 1/2″ to 2″

Product Introduction
Heavy hexagon head bolts manufactured to ASTM A193/A193M Grade B7, the standard specification for chromium-molybdenum alloy steel bolting in high-temperature and high-pressure service. Produced from AISI 4140/4142 alloy steel (1Cr-0.2Mo), oil quenched and tempered at a minimum of 593 °C (1,100 °F). Diameters 1/2″ to 2″ inclusive. Heavy hex dimensions per ASME B18.2.6; UNC coarse threads per ASME B1.1, Class 2A fit. Specified across ASME pressure classes 150 to 2500 as the default bolting material for carbon steel and low-alloy flanged piping in refineries, petrochemical plants, and power generation.

Material & Mechanical Properties
Chromium-molybdenum alloy steel with controlled chemistry: carbon 0.38–0.48%, chromium 0.80–1.10%, molybdenum 0.15–0.25%. The Cr-Mo addition provides hardenability and elevated-temperature strength.

• Minimum tensile strength: 125 ksi (862 MPa) for diameters up to 2-1/2″

• Minimum yield strength: 105 ksi (724 MPa)

• Minimum elongation: 16%

• Minimum reduction of area: 50%

• Hardness: 235–331 HB
  Maximum continuous service temperature is 450 °C (840 °F). Above this limit, yield strength drops rapidly due to tempering effects; ASTM A193 B16 (Cr-Mo-V) should be specified. For low-temperature service below –29 °C, impact-tested ASTM A320 L7 is required. Mechanical and chemical properties are certified by heat lot; Mill Test Reports are available.

Geometry & Thread
Dimensional conformity to ASME B18.2.6 for heavy hex bolts. UNC coarse pitch per ASME B1.1, Class 2A. Width across flats: 1/2″ = 7/8″; 3/4″ = 1-1/4″; 1″ = 1-5/8″; 1-1/2″ = 2-3/8″; 2″ = 3-1/8″. Head height ranges from 21/64″ (1/2″) to 1-7/32″ (2″). Thread length for lengths 6″ and shorter ranges from 1.00″ (1/2″) to 2.75″ (2″). For flange bolting, lengths are determined by the ASME B16.5 stud bolt chart, which specifies length as a function of flange size, pressure class, and gasket thickness.

Marking & Certification
Each bolt is permanently marked with the “B7” grade symbol and the manufacturer’s identification mark in separate locations on the head. Full traceability is maintained through heat code marking, linking each fastener to its Mill Test Report containing chemical and mechanical test results. Grade B7 bolts are paired with ASTM A194 Grade 2H heavy hex nuts, quenched and tempered carbon steel with hardness 248–352 HB and proof load stress 175 ksi for sizes 1″ and under. The 2H nut is the standard companion for B7 in pressure-containing bolting. Washers, where specified, are typically ASTM F436 hardened. EN 10204 Type 3.1 inspection certificates are available on request, providing full heat traceability and mechanical test records.

Application Suitability
High-temperature, high-pressure bolted connections in refineries, petrochemical plants, and power generation facilities. Suitable for all ASME pressure classes from 150 to 2500. The Cr-Mo chemistry maintains strength and creep resistance at elevated temperatures where carbon steel fasteners lose capacity. For applications exceeding 450 °C or requiring impact toughness below –29 °C, alternative grades (B16 or L7) should be specified.