Chloride induced stress corrosion cracking of type 304 and 304L stainless steels in air

Abstract

Chloride stress corrosion cracking (SCC) of Type 304 and 304L austenitic stainless steels (SS) was studied by a constant load method in air at a temperature of 353 K with relative humidity (RH) of 35%. Chlorides simulating sea salt particles were put on the gage section of the SS as droplets of synthetic sea water. The following stress[σap(kgf/mm2)]-minimum rupture time [tf(h)] relationships were obtained for Type 304 and 304 L SS; σap=-51 log(tf) + 153 (304 SS), σap=-141 log(tf) + 386 (304L SS). The threshold stress of SCC was as low as 1/2 of the 0.2% proof stress for solution annealed Type 304 and 304L SS, and smaller than 1/4 of the 0.2% proof stress for sensitized Type 304 SS. This result suggests the difficulty of suppressing SCC by reducing the residual tensile stress of a SS structure. SCC test using NaCl and MgCl2 as chlorides suggested that MgCl2 was responsible for cracking in the test condition of 353 K with RH=35%.