ASTM A302 Grades C and D are manganese-molybdenum (Mn-Mo) alloy steels for boilers and pressure vessels, differing mainly in their nickel content and heat treatment requirements, with Grade D typically having higher nickel for improved properties, both offering excellent strength for high-temperature applications, though Grade C (Mn-Mo-Ni) is often specifically alloyed with nickel for better notch toughness. Both grades aim for similar strength levels (tensile 550-690 MPa, yield >345 MPa) but have distinct chemical compositions and application specifications, especially concerning nickel and heat treatment.
Chemical Composition of ASTM A302 Grade C
ASTM A302 Grade C Chemical Composition | |||||||
Grade | The Element Max (%) | ||||||
C | Si | Mn | P | S | Al | N | |
A302 Grade C | 0.20-0.25 | 0.13–0.45 | 1.07-1.62 | 0,035 | 0,035 |
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Nb | V | Ti | Cu | Cr | Ni | Mo | |
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| 0.37-0.73 | 0.41–0.64 | |
Chemical Composition of ASTM A302 Grade D
ASTM A302 Grade D Chemical Composition | |||||||
Grade | The Element Max (%) | ||||||
C | Si | Mn | P | S | Al | N | |
A302 Grade D | 0.20-0.25 | 0.13–0.45 | 1.07-1.62 | 0,035 | 0.035 |
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Nb | V | Ti | Cu | Cr | Ni | Mo | |
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| 0.67-1.03 | 0.41–0.64 | |
Mechanical Property of ASTM A302 Grade C
Grade |
| ASTM A302 Grade C Mechanical Property | ||
Thickness | Yield | Tensile | Elongation | |
A302 Grade C | mm | Min Mpa | Mpa | Min % |
6-50 | 345 | 550-690 | 20% | |
50-200 | 345 | 550-690 | 17% | |
Mechanical Property of ASTM A302 Grade D
Grade |
| ASTM A302 Grade D Mechanical Property | ||
Thickness | Yield | Tensile | Elongation | |
A302 Grade D | mm | Min Mpa | Mpa | Min % |
6-50 | 345 | 550-690 | 20% | |
50-200 | 345 | 550-690 | 17% | |
Key Differences & Similarities
Composition: Both are Mn-Mo steels, but Grade C often incorporates Nickel (Mn-Mo-Ni), while Grade D also includes Nickel, generally with higher concentrations for enhanced toughness.
Mechanical Properties: They share similar strength ranges, with tensile strengths of 550-690 MPa and minimum yield strength around 345 MPa.
Applications: Used in critical applications like welded boilers, storage tanks, and heat exchangers in oil and gas projects.
Heat Treatment: Plates over 50mm thick must typically be normalized, and supplementary treatments like PWHT (Post-Weld Heat Treatment) or HIC (Hydrogen Induced Cracking) testing can be applied.
Grade C (Mn-Mo-Ni)
Alloy: Manganese-Molybdenum-Nickel.
Benefit: Nickel enhances toughness, making it suitable for demanding high-temperature environments.
Grade D (Mn-Mo-Ni)
Alloy: Manganese-Molybdenum-Nickel.
Key Feature: Contains a higher nickel content compared to Grade C, improving its mechanical properties and toughness.
