A588 has 50 ksi yield and 70 ksi tensile properties. A242, depending on the size/thickness, is either 50 ksi yield and 70 ksi tensile, 46 ksi yield and 67 ksi tensile, or 42 ksi yield and 63 ksi tensile. Under proper conditions, it corrodes by forming a dense and tightly adherent oxide barrier that seals out the atmosphere and retards further corrosion.