Chemical Composition Requirements for ASTM A709
The chemical composition varies among grades and is presented in their respective tables.
Additional Requirements for Grade 50S [345S]
Test reports must also show the tin (Sn) content.
If the tin value is below 0.02%, it may be reported as <0.02%.
0.47% for shapes with flange thickness above 2 in (50 mm)
0.45% for all other shapes
CE is calculated on a heat analysis basis and must be included in the test report.
All grades must be produced as killed steel.
Grades 50W, HPS 50W, and HPS 70W require fine-grain practice.
Grade 50S steel must be manufactured to ensure:
Nitrogen <= 0.015% with nitrogen-binding elements OR
Nitrogen <= 0.012% with or without binding elements
Nitrogen values do not need to be reported.
HPS Grades (50W, 70W, 100W) must be produced using low-hydrogen steelmaking, which may involve vacuum degassing, controlled soaking, slow cooling, or a combination of these methods.
HPS 100W must comply with fine austenitic grain size requirements per A6/A6M.
HPS 50W and HPS 70W may be supplied as:
As-rolled
Control-rolled
For fracture-critical base materials, weld repairs by the supplier or manufacturer are not allowed.
Each grade must meet the specified tensile strength, yield strength, elongation, and hardness levels indicated in the ASTM A709 mechanical property tables.
1. HPS 50W & HPS 70W (Quenched & Tempered Grades)
Steel is heated to >=1650℃F (900℃)
Tempered at >=1100℃F (590℃)
2. HPS 100W
Manufacturer must heat-treat as follows:
Heat to 1600–1700℃F (870–925℃)
Temper at >=1050℃F (565℃) for a duration chosen by the manufacturer
All heat-treat temperatures must be documented on test certificates
Non-Fracture-Critical (T Category) Components
Products intended for tension uses in non-fracture-critical members must undergo impact tests per A673/A673M.
Results must comply with the requirements listed in Table 10.
Fracture-Critical (F Category) Components
Products for fracture-critical tension applications must also be tested in accordance with A673/A673M, following the values specified in Table 11.
1. What are the main applications of A709 steel plates?
A709 steel plates are widely used in structural and infrastructure projects, including:
Load-bearing components requiring high strength and corrosion resistance
2. Is A709 steel weldable?
Yes. ASTM A709 steel offers good weldability with standard welding practices. For thicker plates, preheating may be necessary to prevent cracking and ensure stable weld quality.
3. What is the difference between A709 Grade 50 and A709 Grade 50W?
A709 Grade 50: High-strength structural steel without weathering resistance.
A709 Grade 50W: Weathering steel (similar to Corten) with enhanced atmospheric corrosion resistance and the ability to form a protective rust-like patina.
4. Do A709 steel plates need painting or coating?
A709-50W generally does not require painting, as it develops a natural protective patina that resists corrosion.
However, coatings may still be applied for decorative purposes or when used in high-salinity environments to increase durability.
9. How long does it take for the patina to form on A709-50W?
The patina formation period varies with exposure conditions. Under typical outdoor environments, it usually takes 6 to 36 months for the protective rust layer to fully develop.
10. Can A709 steel be used in coastal environments?
Yes, A709-50W can be used in coastal areas. However, the presence of salt spray can affect patina performance. For direct marine exposure, applying an additional protective coating is recommended for optimal durability.
