The ASTM A606-4 specification is the Standard Steel Specification for High-Strength, Low-Alloy, Hot Rolled, and Cold Rolled Sheet and Strip Steel with Improved Atmospheric Corrosion Resistance for use in structural and other applications. A606 Type 4 steel has a minimum corrosion-resistance index of 6.0 based upon ASTM Guide G101.
It is weldable, formable, punchable, and machinable using the proper techniques. ASTM A606-4 sheet is often used in the unpainted condition as the surface will develop a weathered orange-brown oxide that is resistant to corrosion. It is 20-30% lighter than carbon steel and is used for applications that require high strength-to-weight ratios.