عنوان مقاله [English]
Austenite stainless steel are inclined susceptible to cracking due to stress corrosion in Cl-ion environment; the mode of cracking can be in the form of Trans granular, Inter granular or both of them. The type of crack depends on the concentration of corroding solution, applied stress on specimen, test temperature, chemical composition and metallurgical mode of alloy. In this study, stress corrosion in sensitized 316L austenite stainless steel and the role of surface preparation on postponement of SCC crack initiation has been investigated. Test specimens were made according to ASTM G30 standard by using constant strain technique and then exposed to pure MgCl2 solution with 20, 30, and 40 wt% concentrations at 90oC. For a week, the specimens were taken out of solution everyday and their surface were studied using stereo microscope. With surface treatment such as sand blast and shot blast on specimens, it was found that residual stresses on the specimen surfaces caused crack initiation to significantly postpone in this specimens compared to specimens with untreated surface. Also, the number of cracks in surface-treated specimens were less than untreatment specimens and with an increase in chloride ion concentration in solution, crack initiation time decreases, and the number of cracks and crack depth increase. At the end of tests, the specimens were examined with electronic and optical microscopy and the effect of surface preparing on crack initiation and propagation were investigated. It was observed that, stress corrosion cracks of sensitized AISI 316l alloy initiate from specimen surface and gradually propagate in sensitized grain boundary and change fracture mechanism from Trans granular stress corrosion to inter granular.
 Davis J.R., Handbook of Stainless Steels, ASM International, 1994.
 Stress Corrosion Cracking, Report No. 2295, National Physical Laboratory, London, January 2000.
 ASM Handbook, Corrosion, Fundamental, Testing and Protection, ASM International, 10th Ed., Vol. 13, pp. 197-200, 2003.
 Daniel S. & Kowski J., Selecting tubing materials for power generation heat exchangers, The Proceeding of Power-Gen International Conference, New Orleans, pp. 1-20, USA, December 2007.
 Sedriks A.J., Corrosion of stainless steel, 2nd Ed., Wiley Inter. Science, New York, 1996.
 Ravindranath K. & Malhotra S.N., “The influence of aging on intergranular corrosion of 22 Chromium - 5 Nickel duplex stainless steel”, Journal of Corrosion Science, Vol. 137, pp. 121-132, 1995.
 Bovard F.S., Environmentally induced cracking of an Al-Zn-Mg-Cu alloy, 1st Ed., University of Pittsburgh, Oakland, 2005.
 Damage mechanisms affecting fixed equipment in the refining industry, API 571, American Petroleum Institute, Washington, DC, December 2003.
 Stainless Steels, Chromium- Nickel- Molybdenum, Report No. 316L, ATI Allegheny Ludlum, NACE International, California, 2006.
 ASTM G30, Standard practice for making and using U-bend stress corrosion test specimens, Philadelphia, 2003.
 IPS C TP 101, Surface preparation, Iranian Petroleum Standard, 2004.