ASTM A302 Grades A and B are low-alloy steel plates for pressure vessels, differing mainly in chemical composition (Grade B has more manganese/molybdenum) and mechanical strength, with B offering higher minimum tensile/yield strength, used in boilers and tanks requiring good toughness at moderate temperatures. Grade B typically contains manganese-molybdenum (Mn-Mo) or manganese-molybdenum-nickel (Mn-Mo-Ni) alloying elements for enhanced properties over Grade A.
Chemical Composition
|
A302 Grade A Chemical Composition |
|||||||
|
Carbon, max |
% |
Manganese, max |
% |
Silicon, max |
% |
Sulfur max |
% |
|
25mm or under |
0.2 |
Heat Analysis |
0.95-1.30 |
Heat Analysis |
0.15-0.40 |
All thick |
0.035 |
|
25-50mm |
0.23 |
Product Analysis |
0.87-1.41 |
Product Analysis |
0.13-0.45 |
||
|
over 50mm |
0.25 |
|
|
|
|
||
|
|
|
Molybdenum max |
% |
Nickel max |
% |
Phosphorus |
% |
|
|
|
Heat Analysis |
0.45-0.60 |
Heat Analysis |
… |
All thick |
0.035 |
|
|
|
Product Analysis |
0.41-0.64 |
Product Analysis |
… |
||
|
A302 Grade B Chemical Composition |
|||||||
|
Carbon, max |
% |
Manganese, max |
% |
Silicon, max |
% |
Sulfur max |
% |
|
25mm or under |
0.2 |
Heat Analysis |
1.15-1.50 |
Heat Analysis |
0.15-0.40 |
All thick |
0.035 |
|
25-50mm |
0.23 |
Product Analysis |
1.07-1.62 |
Product Analysis |
0.13-0.45 |
||
|
over 50mm |
0.25 |
|
|
|
|
||
|
|
|
Molybdenum max |
% |
Nickel max |
% |
Phosphorus |
% |
|
|
|
Heat Analysis |
0.45-0.60 |
Heat Analysis |
… |
All thick |
0.035 |
|
|
|
Product Analysis |
0.41-0.64 |
Product Analysis |
… |
||
Mechanical Property
|
Mechanical Property of A302 Grade A steel plate |
A302 Grade A |
|
Tensile strength, kis [MPa] |
75-95 [515-655] |
|
Yield strength, min, kis [MPa] |
45 [310] |
|
Elongation in 8 in. [200 mm], min, % |
15 |
|
Elongation in 2 in. [50 mm], min, % |
19 |
|
Mechanical Property of A302 Grade B steel plate |
A302 Grade B |
|
Tensile strength, kis [MPa] |
80-100 [550-690] |
|
Yield strength, min, kis [MPa] |
50 [345] |
|
Elongation in 8 in. [200 mm], min, % |
15 |
|
Elongation in 2 in. [50 mm], min, % |
18 |
Key Differences & Characteristics
ASTM A302 Specification: Both fall under ASTM A302, a standard for pressure vessel plates, but have different strength levels.
Chemical Composition: Grade B includes higher percentages of manganese and molybdenum compared to Grade A, enhancing its strength and toughness.
Mechanical Properties: Grade B has significantly higher minimum yield strength (e.g., 345 MPa) and tensile strength (e.g., 550-690 MPa) than Grade A.
Applications: Used for fabricating boilers, pressure vessels, and storage tanks where moderate temperatures and good weldability are required.
