Generally austenitic stainless steels are susceptible for Stress Corrosion Cracking (SCC). The SCC of them (type 316 and type 304) was extensively investigated as functions of applied stress (σ), sensitizing temperature, sensitizing time, applied potential and environmental factors ( inhibitor, sensitizing time, pH, anion concentration, anion species and test temperature) by using a constant load method [1]. The change in the mechanism for SCC on AISI 304 austenitic stainless steel was investigated in 42wt% boiling saturated magnesium chloride solution by using a constant load method. Three parameters (time to failure; tf steady-state elongation rate ; iss and transition time at which a linear increase in elongation to deviate; tss) obtained from the corrosion elongation curve showed three regions ; stress – dominated, stress corrosion cracking dominated and corrosion – dominated regions [2]. AISI 304 are prone to microstructural changes when exposed to sensitization temperatures due to heat treatment. Precipitation of chromium carbide takes place along the grain boundary regions in the temperature range of 480oC to 815oC. These results in chromium depletion near the grain boundary, and the resultant grain –boundary region is susceptible to intergranular corrosion (IGC)[3]. The extent of which depends upon the degree of sensitization. The Cr depletion zone, while the Cr carbide would serve as an barrier of dislocation movement [4]. Nishimura demonstrated that the most severe SCC susceptibility took place at a sensitizing temperature of ~931 K (6600C) in hydrochloric acid solution[5]. Deformation of metastable austenite phase involves the formation of strain –induced ε α’-martensite[6]. Austenitic stainless steel can undergo phase transformation due to applied stress or hydrogen charging.
Reference:
[1] Rokuro Nishimura, Characterization and perspective of stress corrosion cracking of austenitic stainless steels (type 304 and type 316) in acid solutions using constant load method, Corrosion Science 49 (2007) 81–91
[2] O.Alyousif, R.Nishumura, The stress corrosion cracking behavior of austenitic stainless steels in boiling magnesium chloride solutions, Corrosion Science 49 (2007) 3040–3051
[3] Raghuvir Singh; B Ravikumar; A Kumar; P K Dey; I Chattoraj, The effects of cold working on sensitization and intergranular corrosion behaviour of AISI 304 Stainless Steel, Metallurgical and Materials Transactions; Nov 2003; 34A, 11; Academic Research Library pg. 2441
[4] G.E.Dieter, Mechanical Metallurgy. 2nd ed, McGraw-Hill 1976 p.195
[5] R Nishimura; I Katim; Y Maeda, Stress corrosion cracking of sensitized type 304 stainless steel in hydrochloric acid solutions- Predicting Time to failure and Effect of sensitizing Temperature, Corrosion; Oct 2001; 57, 10; ProQuest Science Journals.pg. 853
[6] Juho Talonen, Metallurgical and Materials Transactions; Feb 2005; 36A, 2; Academic Research Library pg. 421
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