ASTM A320 specification covers bolting materials for low-temperature service and applications where high strength and good toughness are required. It includes several grades of alloy and stainless steel bolts, stud bolts, screws, and nuts for use in pressure vessels, valves, flanges, and other equipment.
Grade B8M Stud Bolt is made from 316 stainless steel, a type of fastener designed for use in pressure vessels, flanges, valves, and other high-stress applications, particularly in environments where corrosion resistance and low-temperature toughness are critical.
Chemical Composition:
The chemical composition of Grade B8M is the same as 316 stainless steel.
| Element | Content (%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Chromium (Cr) | 16.0–18.0 |
| Nickel (Ni) | 10.0–14.0 |
| Molybdenum (Mo) | 2.0–3.0 |
| Iron (Fe) | Balance |
2. Heat Treatment:
- B8M Class 1:
- Solution annealed for maximum corrosion resistance and ductility.
- Heated to a temperature of 1900°F (1040°C) or above, then quenched to retain austenitic structure.
- Enhances corrosion resistance, especially against pitting and crevice corrosion in chloride environments.
- B8M Class 2:
- Strain-hardened to achieve higher tensile and yield strength.
- Not suitable for further heat treatment after strain hardening.
- Offers a balance of strength and corrosion resistance but slightly reduced ductility compared to Class 1.
3. B8M Stud Bolt Hardness:
| Class | Hardness (Maximum) |
|---|---|
| Class 1 | HRB 95 |
| Class 2 | HRC 35 |
- Class 1 has a softer structure with excellent toughness.
- Class 2 is harder due to strain hardening, providing higher tensile and yield strength.
4. B8M Stud Bolt Marking:
Each fastener is marked to ensure traceability and compliance with ASTM A320 standards.
- Grade: Marked as “B8M” to indicate the material grade.
- Class 2
- marked as SH, SH means Strain Hardened,
- Absence of Class marking indicates Class 1.
- Manufacturer’s Identification: Unique mark for the producer or supplier.
5,Mechanical Properties:
| Property | B8M Class 1 | B8M Class 2 |
|---|---|---|
| Tensile Strength | 75 ksi (minimum) | 100 ksi (minimum) |
| Yield Strength (0.2%) | 30 ksi (minimum) | 65 ksi (minimum) |
| Elongation | 30% (minimum) | 20% (minimum) |
ASTM A194 Grade 8M Hex Nuts for B8M stud bolt
ASTM A194 Grade 8M Hex Nuts are made from 316 stainless steel, offering high corrosion resistance and strength