Stress corrosion crack growth studies on nitrogen added AISI type 316 stainless steel and its weld metal in boiling acidified sodium chloride solution using the fracture mechanics approach

摘要

Compact tension specimens of nitrogen-added AISI type 316 austenitic stainless steel and its weld metal were subjected to stress corrosion cracking (SCC) testing in a boiling solution containing SM sodium chloride +0.15 M sodium sulphate + 2.5 ml/l hydrochloric acid solution using the constant extension rate testing (CERT) technique. The extension rate of testing was 10 microns per hour. The threshold values of stress intensity factor (K{sub}(ISCC)) and J-integral (J{sub}(ICSS)) were taken as those values of K{sub}I and J{sub}I at which about 25 microns of SCC crack growth was observed. These threshold values were about four times higher and plateau crack growth rates (PCGR) were nearly one order of magnitude lower for the base metal vis-a-vis the weld metal. Fractographic observations indicated failure by transgranular SCC (TGSCC) of austenite in both the base and weld metal. No stress-assisted dissolution of delta-ferrite or its interface with austenite, was observed.