What Is SA573 Grade 65 Steel?
SA573 Grade 65 is a structural carbon steel plate of improved toughness specified under ASME SA573, corresponding to ASTM A573/A573M. The A573 family contains Grades 58, 65, and 70, and it is a carbon steel series developed for applications that need better notch toughness than ordinary structural carbon plates. It is not a high-strength low-alloy steel, and there is no Grade 60 in the specification. The number in the designation refers to the tensile strength level: the 65 indicates the 65-77 ksi tensile range.
Mechanical Properties per ASTM A573
For Grade 65, the minimum yield strength is 35 ksi (240 MPa) for plate up to 3/4 in thick, and the tensile strength range is 65-77 ksi (450-530 MPa). Minimum elongation is specified by the standard according to gage length and thickness. The combination of moderate strength and improved notch toughness makes the grade suitable for welded structures and components that experience impact or dynamic loading.
Chemical Composition
For Grade 65 plate up to 3/4 in thick, the heat analysis limits are: carbon 0.26% max, manganese 0.85-1.20%, phosphorus 0.035% max, sulfur 0.040% max, and silicon 0.15-0.40%. The controlled composition supports the improved toughness and good weldability of the grade; confirm the values for thicker plate against the applicable table of ASTM A573/A573M.
Comparison of A573 Grades 58, 65, and 70
Grade 58 provides a minimum yield of 32 ksi (220 MPa) with a tensile range of 58-71 ksi (400-490 MPa). Grade 65 provides 35 ksi (240 MPa) with 65-77 ksi (450-530 MPa). Grade 70 provides 42 ksi (290 MPa) with 70-90 ksi (485-620 MPa). Higher grades in the family therefore support heavier loads and allow lighter members for the same performance, while all three grades share the improved toughness and weldability that define the A573 family.
Typical Applications
A573 Grade 65 is used for bridges, industrial machinery, crane components, and load-bearing structural elements where improved toughness is required together with moderate strength. Grade 58 suits general structural use, and Grade 70 is chosen for the highest loads within the family, including heavier bridge and machinery components.
Frequently Asked Questions
Does ASTM A573 include a Grade 60? No. A573/A573M contains only Grades 58, 65, and 70; any Grade 60 data published for this specification is incorrect.
What is the yield strength of A573 Grade 65? The minimum yield strength is 35 ksi (240 MPa) for plate up to 3/4 in thick; the 65 in the name refers to the tensile range, not the yield.
Is A573 a high-strength low-alloy steel? No. A573 is a carbon steel series of improved toughness; it does not use HSLA alloying such as vanadium or niobium.
How does Grade 65 compare with Grade 58? Grade 65 has a higher minimum yield of 35 ksi (240 MPa) versus 32 ksi (220 MPa) and a higher tensile range, making it suitable for heavier loads.
What is the chemical composition of A573 Grade 65? Maximum carbon 0.26%, phosphorus 0.035%, and sulfur 0.040%, with manganese 0.85-1.20% and silicon 0.15-0.40%.
Where is A573 Grade 65 used? In bridges, industrial machinery, crane components, and load-bearing structural elements where improved toughness is required.
