Corrosion of 18Ni 180 and 18Ni 200 Maraging Steels in Chloride Environments

Abstract

18Ni 180 and 18Ni 200 maraging steels have shown high resistance to stress corrosion cracking in sea water. U-bends had no cracks after exposure for over three years. 18Ni 180 welds also had good resistance, but welds in the 18Ni 200 grade suffered stress corrosion cracking. Cathodic protection of U-bends was beneficial, although a sensitivity to hydrogen was observed at very negative potentials. Fracture toughness measurements in sea water and 3-1/2% NaCI gave KISCC values of 130 ksi (in)1/2 for the 18 Ni 180 steel and 94 ksi (in)1/2 for 18Ni 200. The corresponding values for welds were 122 ksi (in)1/2 and 70 ksi (in)1/2. Fracture toughness decreased when the precracked cantilever bars were coupled to zinc or, in the case of welds, held at −0.85 volt vs SCE. General corrosion rates of maraging steels in sea water and marine atmospheres were approximately half those of HY-80 and 4340 low alloy steels.