Effects of Temperature and Pressure on Stress Corrosion Cracking Behavior of 310S Stainless Steel in Chloride Solution

310S is an austenitic stainless steel for high temperature applications, having strong resistance of oxidation, hydrogen embrittlement and corrosion. Stress corrosion cracking（SCC） is the main corrosion failure mode for 310S stainless steel. Past researched about SCC of 310S primarily focus on the corrosion mechanism and influence of temperature and corrosive media, but few studies concern the combined influence of temperature, pressure and chloride. on SCC of 310S stainless steel, prepared samples are investigated via For a better understanding of temperature and pressure＇s effects slow strain rate tensile test（SSRT） in different temperature and pressure in NACE A solution. The result shows that the SCC sensibility indexes of 310S stainless steel increase with the rise of temperature and reach maximum at 10MPa and 160~C, increasing by 22.3% compared with that at 10 MPa and 80 ℃. Instead, the sensibility decreases with the pressure up. Besides, the fractures begin to transform from the ductile fracture to the brittle fracture with the increase of temperature. 310S stainless steel has an obvious tendency of stress corrosion at 10MPa and 160℃ and the fracture surface exists cleavage steps, river patterns and some local secondary cracks, having obvious brittle fracture characteristics. The SCC cracks initiate from inclusions and tiny pits in the matrix and propagate into the matrix along the cross section gradually until rupture. In particular, the oxygen and chloride play an important role on the SCC of 310S stainless steel in NACE A solution. The chloride damages passivating film, causing pitting corrosion, concentrating in the cracks and accelerated SSC ultimately. The research reveals the combined influence of temperature, pressure and chloride on the SCC of 310S, which can be a guide to the application of 310S stainless steel in super-heater tube.

Oxidation Behavior of Micro-Crystalline Coatings of 310S Stainless Steel

Micro-crystalline coatings of 310S stainless steels were produced by unbalanced magnetron sputter deposition. Isothermal oxidation behavior of the coated and uncoated specimens has been studied using a thermogravimetric analysis (TGA) station. The oxidation time was 50h and the temperature was 1 000℃. The oxidation rates of thecoated specimens was found to be much lower than the uncoated specimens after 50 h of oxidation. The oxidationkinetic curves of the coated specimens consisted of three stages : approximately parabolic at the first stage, speedingup at the second stage, and slow down at the third stage. The increase of the oxidation rate at the second stage nasattributed to the fast diffuison of Fe though the fine grained Cr2O3 layer formed on the micro-crystalline coatings.The top view and cross-section microstructures of the oxides formed on the coated and the uncoated specimens werestudied with SEM and EDS. It was observed that the nucleation of oxide on the coated specimens was muchenhanced at the initial oxidation stage. This was explained as the result of reduction in the critical free energychange and increase in the supply of chromium ions.