Core Chemical Composition (Weight %)
The chemical composition of ASTM A204 Grade B steel is optimized for high-temperature pressure applications. Key elements include:
| Element | Range (%) | Function |
|---|---|---|
| Carbon (C) | 0.20–0.27 | Enhances strength and hardness |
| Manganese (Mn) | 0.90–0.98 | Improves hardenability and tensile strength |
| Molybdenum (Mo) | 0.41–0.64 | Boosts high-temperature strength and creep resistance |
| Silicon (Si) | 0.13–0.45 | Deoxidizes steel and enhances toughness |
| Phosphorus (P) | ≤0.035 | Reduces ductility and impact resistance (controlled) |
| Sulfur (S) | ≤0.035 | Increases brittleness (minimized) |
Notes:
Molybdenum is the key alloying element, enabling stability under high-pressure and high-temperature conditions.
Strict limits on P and S minimize brittleness and improve weldability.
Mechanical Properties
ASTM A204 Grade B offers balanced strength and ductility:
Tensile Strength: 485–620 MPa
Yield Strength: ≥275 MPa
Elongation:
21% (over 50 mm gauge length)
17% (over 200 mm gauge length)
Hardness: ~170 HB (Brinell)
Impact Toughness: Charpy impact tested at -20°C to -46°C for low-temperature applications.
Thermal and Physical Properties
Maximum Service Temperature: 410°C (760°F)
Thermal Conductivity: 52 W/m·K
Thermal Expansion: 13 µm/m·K
Density: 7.9 g/cm³
Applications
This steel is designed for critical high-pressure environments:
Pressure Vessels & Boilers: Reactors, heat exchangers, and steam drums in power plants.
Oil & Gas Equipment: Storage tanks, pipelines, and refineries (resists H₂S corrosion when NACE MR0175-compliant).
Structural Components: Ship hulls, aerospace parts, and industrial machinery.
Manufacturing and Quality Control
Production Techniques:
Vacuum degassing (removes impurities).
Thermo-Mechanical Controlled Processing (TMCP) (enhances microstructure).
Testing Standards:
Ultrasonic testing (per SA-578).
Heat treatment: Furnace normalization.
Supplementary tests: HIC (Hydrogen-Induced Cracking), NACE MR0175 (sour service).
Equivalent Grades and Standards
International Equivalents:
AFNOR (France): 15CD 2.05
EN (EU): 16Mo3
Dimensions:
Thickness: 6–150 mm
Width: Up to 4,050 mm.
Key Notes for Selection
Carbon Variability: Higher carbon content (vs. Grade A) increases strength but may reduce weldability.
Corrosion Resistance: Molybdenum content provides resistance to reducing acids and pitting.
Thickness Limitation: Max 150 mm due to mechanical property consistency.
For detailed specifications, refer to ASTM A204/A204M standards.
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