"Weathering" means that due to their chemical compositions, these steels exhibit increased resistance to atmospheric 

corrosion compared to other steels. This is because the steel forms a protective layer on its surface under the influence

of the weather.

The corrosion-retarding effect of the protective layer is produced by the particular distribution and concentration

of alloying elements in it. The layer protecting the surface develops and regenerates continuously when subjected to

the influence of the weather. In other words, the steel is allowed to rust in order to form the 'protective' coating.

The mechanical properties of weathering steels depend on which alloy and how thick the material is.

ASTM A 242

The original A 242 alloy has a yield strength of 50,000 pounds per square inch (340,000 kPa) and ultimate tensile strength

of 70,000 psi (480,000 kPa) for light-medium rolled shapes and plates up to 0.75 inches (19 mm) thick.

It has yield strength of 46,000 psi (320,000 kPa) and ultimate strength of 67,000 psi (460,000 kPa) for medium

weight rolled shapes and plates from 0.75–1 inch (19–25 mm) thick. The thickest rolled sections and plates – from 1.5–4 in (38–102 mm) thick have yield strength of 42,000 psi (290,000 kPa) and ultimate

strength of 63,000 psi (430,000 kPa).

ASTM A 588

A 588 has a yield strength of at least 50,000 psi (340,000 kPa), and ultimate tensile strength of 70,000 psi (480,000 kPa)

for all rolled shapes and plate thicknesses up to 4 in (100 mm) thick. Plates from 4–5 in (102–127 mm) have yield

strength at least 46,000 psi (320,000 kPa) and ultimate tensile strength at least 67,000 psi (460,000 kPa), and plates from 5–8 in (127–203 mm) thick have yield strength at least 42,000 psi (290,000 kPa) and ultimate tensile strength

at least 63,000 psi (430,000 kPa).

ASTM A606-4

ASTM A606-4 is a high strength, low alloy specification with improved atmospheric corrosion properties covering hot and

cold rolled steel sheet, strip and coil. A606-4 contains additional alloying elements and provides a level of corrosion resistance

substantially better than that of carbon steels with or without copper addition. ASTM A606-4 has a 50ksi minimum yield

strength and a 70ksi minimum tensile strength. A606-4 is supplied in 2 types. Type 2 contains 0.20 minimum copper based

on cast or heat analysis (0.18 minimum Cu for product check). Type 4 contains additional alloying elements and provides a level

of corrosion resistance substantially better than that of carbon steels with or without copper addition.

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