STRESS-CORROSION CRACKING OF 15CR-15NI-2.2MO TITANIUM-MODIFIED AUSTENITIC STAINLESS-STEELS

The stress-corrosion cracking (SCC) behavior of two alloys of titanium-modified austenitic stainless steels with different Ti/C ratios in the 20% cold worked condition was studied in 45% boiling magnesium chloride (BP 427 K) using the constant-extension rate testing (CERT) technique. The SCC susceptibility of the two titanium-modified alloys was assessed using the ratios of the values of ultimate tensile strength (UTS) and percent elongation in magnesium chloride and liquid paraffin, the susceptibility index (1), crack propagation rates (CPR), and stress ratios at different values of plastic strains. The results obtained on these alloys were compared with AISI type 316 stainless steel. It was observed that the two titanium-modified austenitic stainless steels had better SCC resistance than type 316 stainless steel, mainly due to their higher nickel content and, to a lesser extent, to the presence of titanium. Increasing the value of the Ti/C ratio led to increased SCC resistance due to the availability of more free titanium in the solid solution. Fractography of the failed samples indicated failure by a combination of transgranular SCC and ductile fracture.