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| Property | Value |
|---|---|
| ASTM Standard | A193/A193M Grade B7 |
| UNS Number | G41400 (AISI 4140/4142) |
| Tensile Strength | 125 ksi (860 MPa) min |
| Yield Strength | 105 ksi (720 MPa) min |
| Max Service Temperature | 538°C (1000°F) |
| Hardness | 235–321 HB |
| Element | Composition (%) |
|---|---|
| C | 0.38–0.48 |
| Cr | 0.80–1.10 |
| Mo | 0.15–0.25 |
| Mn | 0.75–1.00 |
| Si | 0.15–0.35 |
| P | ≤0.035 |
| S | ≤0.040 |
ASTM A193 Grade B7 is a chromium-molybdenum alloy steel fastener material, typically manufactured from AISI 4140 or 4142 grade steel. Chromium enhances hardenability and provides moderate corrosion resistance, while molybdenum improves strength retention at elevated temperatures and reduces temper embrittlement. Carbon content, generally between 0.38-0.48%, allows the material to achieve high tensile and yield strength through quenching and tempering heat treatment. Manganese and silicon further contribute to hardenability and deoxidation during steel production, ensuring a uniform, fine-grained microstructure suitable for demanding bolting applications.
The resulting quenched and tempered microstructure delivers excellent mechanical strength, fatigue resistance and dimensional stability under high preload conditions. Grade B7 offers reliable performance up to 538°C, making it ideal for high-temperature and high-pressure flange connections in petrochemical, power generation and pipeline industries. Although not stainless, its balanced alloy composition provides adequate atmospheric corrosion resistance for industrial service when properly coated or plated. These combined properties make B7 the industry-standard choice for critical stud bolts, hex bolts and threaded fasteners requiring superior strength and long-term reliability.
Specifications
ASTM A193 Grade B7 Fasteners conform to ASTM A193 requirements for alloy steel bolting, combining high tensile strength, controlled hardness, and reliable dimensional tolerances for threaded fastener applications in elevated-temperature service. The specification defines mechanical performance, thread dimensions, and size-controlled technical data.
| Property | Value |
|---|---|
| Tensile Strength | 860 MPa (125 ksi) min |
| Yield Strength | 720 MPa (105 ksi) min |
| Elongation | 16% min in 2 in. |
| Reduction of Area | 50% min |
| Hardness | 235–321 HB (99 HRB max not applicable) |
| Modulus of Elasticity | 205 GPa (29,700 ksi) |
| Thermal Expansion | 12.2 µm/m°C (0-100°C) |
| Thermal Conductivity | 42.6 W/m·K |
| Density | 7.85 g/cm³ |
| Melting Range | 1420-1460°C |
| Heat Treatment | Quenched and Tempered |
| Max Service Temperature | 538°C (1000°F) |
| Standard/Feature | Details |
|---|---|
| Bolt Standard | ASME B18.2.1, DIN 931/933 |
| Stud Bolt Standard | ASME B16.5, MSS SP-75 |
| Nut Standard | ASTM A194 Grade 2H/7 |
| Washer Standard | ASME B18.22.1 |
| Thread Form | UNC, UNF, 8-UN Series |
| Diameter Range | 1/4 in to 4 in (M6 to M100) |
| Length Range | 25 mm to 1000 mm (custom on request) |
| Available Product Forms | Hex Bolts, Stud Bolts, Threaded Rods |
| Custom Sizes | Available on request |
| Manufacturing Standards | ASTM A193/A193M |
| Inspection Standards | NACE MR0175, PMI Testing |
| Coating Options | Plain, Zinc, PTFE, Xylan |
Applications
