What are difference between A517 Grade A and A517 Grade B？

ASTM A517 is a standard specification for high-strength, quenched and tempered alloy steel plates primarily intended for use in fusion welded boilers and pressure vessels . Both Grade A and Grade B fall under this specification and share the same fundamental mechanical property requirements, but they differ slightly in chemical composition to achieve these properties.

Common Characteristics:
Both Grade A and Grade B are supplied in the quenched and tempered condition, which imparts an excellent combination of high strength and toughness . They have a minimum yield strength of 100 ksi (690 MPa) and a tensile strength range of 115-135 ksi (795-930 MPa) for thicknesses up to 1.25 inches (32 mm) . This high strength-to-weight ratio makes them ideal for applications requiring reduced section thickness and weight savings in critical components . Typical applications include pressure vessels, boilers, and other highly stressed structures .

Key Differences:
The primary distinction between the two grades lies in their specified alloying elements, although some supplier data indicates overlapping ranges:

ASTM A517 Grade A: This grade utilizes a combination of chromium, molybdenum, and a small amount of boron to achieve its hardenability and strength . Some sources also indicate the addition of zirconium (Zr) as a grain refiner in Grade A . Its silicon content is generally higher than Grade B .

ASTM A517 Grade B: Like Grade A, it relies on chromium, molybdenum, and boron additions . However, Grade B typically has a lower silicon range compared to Grade A . While some data shows identical composition ranges for Cr, Mo, and B in both grades , others indicate slight variations, particularly in elements like silicon . Notably, some sources suggest Grade B may be selected for enhanced low-temperature toughness or performance in specific environments, though both grades meet Charpy V-Notch impact requirements at similar temperatures.

Chemical Composition

Mechanical Property