EFFECT OF RESIDUAL STRESS AND STRAIN GENERATED DURING MANUFACTURING PROCESS ON THE STRESS CORROSION CRACKING SUSCEPTIBILITY OF AUSTENITIC STAINLESS STEEL

摘要

The various stages that the stainless steel tube undergoes in the course of fabrication decide the nature and level of residual stress induced in the final tubing. The effect of residual stress on the stress corrosion cracking susceptibility of 304 stainless steel was studied by subjecting these tubing to boiling magnesium chloride test as per ASTM G 36 for different time periods followed by detailed characterization. In order to understand the effect of plastic deformation caused due to the surface working operations (primarily machining) on the stress corrosion cracking susceptibility of austenitic stainless steel, a plate of 304L SS subjected to a definite amount of machining was exposed a) to boiling magnesium chloride environment for 24h and b) to 5 N H_2SO_4 + 0.5 N NaCl solution at 26°C for 168 h (7 days). In addition, solution annealed 304L were subjected to ～10% strain, by producing constant strain sample as per ASTM G 30, and were exposed to the same environment as that for the machined sample, It has been shown that the tests used were sensitive to not only the magnitude but also to the direction (circumferential vs. longitudinal) of the residual stresses. Surface machining was shown to drastically increase the susceptibility of the stainless steel to chloride stress corrosion cracking.