ASTM A325 Type 1
Made from medium-carbon steel (typically alloyed with boron).
No inherent corrosion resistance; requires galvanization or coatings for outdoor use.
Standard choice for general structural connections (e.g., steel buildings, bridges with protective coatings).
ASTM A325 Type 3
Made from weathering steel (similar to ASTM A588).
Forms a protective rust patina when exposed to weather, eliminating the need for coatings in most environments.
Used in exposed applications (e.g., bridges, transmission towers) where long-term corrosion resistance is critical.
Critical Notes:
Both types have identical mechanical properties (e.g., tensile strength: 120/105 ksi min).
Type 3 is not stainless steel-it develops a patina but may still corrode in highly aggressive (e.g., coastal) environments.
Do not mix Type 1 and Type 3 in the same joint due to galvanic corrosion risks.
