Introduction to ASTM A517 Grade Q Steel Plate
ASTM A517 Grade Q is a high strength quenched and tempered alloy steel plate produced under the ASTM A517/A517M specification for pressure vessel applications. The grade is designed around a low carbon, boron treated alloy concept combined with zirconium, which together deliver high strength, good toughness and reliable hardenability in heavy sections. Plates conforming to this grade are used where a 690 MPa class tensile strength is needed in a welded pressure vessel, an offshore structure or a heavily loaded item of mobile equipment.
The performance of the grade depends on close control of three things: the alloy balance in the heat, the austenitizing and quenching practice, and the tempering temperature. When those three are aligned, the plate combines very high yield strength with sufficient ductility and low temperature toughness for fabrication by welding and forming.
Chemical Composition
The typical chemical composition of ASTM A517 Grade Q plate is shown below. Carbon is kept in a narrow band and boron is capped at a very low level, because even small additions of boron have a strong effect on hardenability.
| Element | Content (%) |
|---|---|
| C | 0.15 - 0.21 |
| Si | 0.40 - 0.80 |
| Mn | 0.80 - 1.10 |
| P | 0.035 max |
| S | 0.035 max |
| Cr | 0.50 - 0.80 |
| Mo | 0.18 - 0.28 |
| B | 0.0025 max |
| Zr | 0.05 - 0.15 |
Mechanical Properties
Mechanical requirements are specified in the quenched and tempered condition, so test specimens are taken from plate that has received the full heat treatment cycle. The table below summarises the typical property requirements.
| Property | Requirement |
|---|---|
| Yield strength | 510 MPa min |
| Tensile strength | 690 - 930 MPa |
| Elongation after fracture | 15 % min |
In addition to room temperature tensile testing, the grade is recognised for superior hardenability, which means that the strength and toughness achieved at the surface of a thick plate are also developed at mid thickness. This is the property that makes the steel suitable for thick walled pressure components and for structural nodes in offshore construction, where the full section must carry load reliably.
Heat Treatment and Low Temperature Impact Testing
ASTM A517 Grade Q plate is heat treated as follows:
Austenitizing at a temperature not lower than 900 °C to dissolve the alloying elements and refine the austenitic grain structure
Quenching in water or oil, with the quench intensity matched to plate thickness so that the core cools fast enough to transform to a hard, fine grained structure
Tempering at a temperature not lower than 620 °C to restore ductility and toughness while retaining high strength
Low temperature impact testing is carried out on the heat treated plate as a routine verification of toughness. The steel is intended to work in cold climates and in offshore environments, so impact energy is checked to confirm that the quenched and tempered microstructure keeps its resistance to brittle fracture when the service temperature falls well below freezing. Impact testing also serves as a quality check on the tempering practice, because an under tempered plate shows poor toughness even when its tensile strength is correct.
Available Dimensions and Applications
Plates are available in thickness from 8 mm to 180 mm, width from 1600 mm to 2500 mm and length from 6000 mm to 12000 mm, and they can be supplied cut to size, edge prepared or surface treated according to the fabrication drawing.
Typical applications include:
Ocean platform construction and offshore structural components
Mining equipment and machinery subject to high impact loading
Heavy duty construction machinery such as drillers, excavators, loaders and bulldozers
Pressure vessels and boiler components working at high stress
Hydraulic support structures in coal mines
Cranes, lifting equipment and other heavily loaded welded fabrications
FAQ about ASTM A517 Grade Q Steel Plate
Q: Which specification covers A517 Grade Q plate?
The grade is covered by ASTM A517/A517M, the standard specification for pressure vessel plates, alloy steel, high strength, quenched and tempered.
Q: What are the mechanical properties of A517 Grade Q?
Typical requirements are a minimum yield strength of 510 MPa, a tensile strength range of 690 to 930 MPa and a minimum elongation after fracture of 15 %.
Q: Why is the plate quenched and tempered?
The heat treatment produces a fine grained tempered martensitic or bainitic structure that combines high strength with the toughness needed for welded pressure and structural service.
Q: At what temperature is it tempered?
Tempering is carried out at a temperature not lower than 620 °C after water or oil quenching from an austenitizing temperature of at least 900 °C.
Q: What sizes are available?
Thickness from 8 mm to 180 mm, width from 1600 mm to 2500 mm and length from 6000 mm to 12000 mm, with cut to size options.
Q: Where is A517 Grade Q plate used?
It is used for offshore platform structures, mining and earthmoving machinery, hydraulic supports, pressure vessels and other heavily loaded welded equipment that must also perform in low temperature environments.
