What Is SA573 Grade 70 Steel?
SA573 Grade 70 is a structural carbon steel plate of improved toughness specified under ASME SA573, corresponding to ASTM A573/A573M. The A573 family is not a high-strength low-alloy series; it is a carbon steel series developed for applications that need better notch toughness than ordinary structural carbon plates. The family contains Grades 58, 65, and 70, and the standard applies to plates up to 1.5 in (about 40 mm) thick.
Chemical Composition
For Grade 70 plate up to 3/4 in thick, the heat analysis limits are: carbon 0.28% 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 and for product analysis against the applicable table of ASTM A573/A573M.
Mechanical Properties per ASTM A573
For Grade 70, the minimum yield strength is 42 ksi (290 MPa) for plate up to 3/4 in thick, and the tensile strength range is 70-90 ksi (485-620 MPa). Minimum elongation is specified by the standard according to gage length and thickness, and it decreases with increasing thickness. Grade 65 provides a minimum yield of 35 ksi (240 MPa) with a tensile range of 65-77 ksi (450-530 MPa), and Grade 58 provides 32 ksi (220 MPa) with a tensile range of 58-71 ksi (400-490 MPa).
Applications and Fabrication
Because of its improved toughness, SA573 Grade 70 is used for storage tanks, pressure vessel components, bridges, and structural elements where impact resistance matters more than very high strength. The steel welds well with conventional processes, and standard practices for carbon steel apply; for thicker sections, preheating may be recommended depending on the joint design and shop conditions.
Notes on Cross-Standard Substitution
There is no widely accepted direct equivalent of A573 Grade 70 in the EN or GB systems, because the combination of a 42 ksi minimum yield with improved toughness is specific to the A573 family. Higher-strength structural grades such as A572 Grade 65, EN S460, or GB Q460-type steels are sometimes considered in structural substitution because their higher strength is conservative, but the design values, toughness requirements, and thickness limitations must be verified against the governing code before substitution.
Frequently Asked Questions
What is SA573 Grade 70 steel? It is a structural carbon steel plate of improved toughness specified under ASTM A573/A573M, with a minimum yield strength of 42 ksi (290 MPa) and a tensile range of 70-90 ksi (485-620 MPa).
Is SA573 Grade 70 a high-strength low-alloy steel? No. A573 is a carbon steel series; the 70 refers to the tensile strength level, not the yield strength.
What grades are included in ASTM A573? The standard covers Grades 58, 65, and 70, and it applies to plates up to 1.5 in (about 40 mm) thick.
What is SA573 Grade 70 used for? Storage tanks, pressure vessel components, bridges, and structural applications where improved notch toughness is required.
What is the chemical composition of SA573 Grade 70? For plate up to 3/4 in, maximum carbon 0.28%, manganese 0.85-1.20%, phosphorus 0.035%, and sulfur 0.040%, with silicon 0.15-0.40%.
What is SA573 Grade 70 equivalent to? There is no widely accepted direct EN or GB equivalent; higher-strength grades such as S460 or Q460-type steels are sometimes substituted after verifying the design requirements against the governing code.
