Papers by Keyword: Sensitization

Abstract: This paper presents a metallographic and fractographic study of AISI 304 austenitic stainless steel subjected to mechanical loading in the sensitized condition. Static three-point bending tests and impact tests were carried out to evaluate how sensitization affects the mechanical response and fracture behaviour of AISI 304. The study compares the initial state of the material with its condition after sensitization at 700 °C for 10 h, with emphasis on changes in plastic deformation and fracture mechanisms. Microstructural evaluation was performed using light microscopy, while Vickers microhardness measurements provided insight into local mechanical changes. Fractographic analysis using scanning electron microscopy revealed differences in fracture surface morphology. Results demonstrate a decrease in microhardness, reduced impact energy, and noticeable differences in fracture morphology following the sensitization treatment, indicating that the heat treatment influences both the mechanical response and failure behaviour of AISI 304.

Abstract: Austenitic stainless steels tend to form chromium depletion zones during welding. The chromium combines with available carbon around the grain boundaries to produce chromium-deficient areas, thus becoming susceptible to intergranular corrosion. The sensitization phenomenon of 304 stainless steel during gas tungsten arc welding (GTAW) process has been investigated. In this experiment, there were four welded samples observed. Two welded samples were cooled in air and cooled in oil immediately after welding, respectively. Meanwhile, another two welded samples were normalized by heated to 800 and 900 °C and held for 0.5 h before cooled in air. The welded samples were analyzed using optical microscopy, scanning electron microscopy and energy dispersive microscopy (SEM-EDS), and a Vickers hardness testing machine. The results show that normalizing affects significant changes in the microstructure due to the sensitization phenomenon. It can be seen that there is more carbide deposition in the welded sample with cooled in air and welded samples which normalized by heated to 800 °C and 900 °C and held for 0.5 h before being cooled in air. Meanwhile, the sample that was cooled in oil immediately after welding showed fewer chromium carbides. Normalizing the welded samples to 800 and 900 °C and holding it for 0.5 h before cooling in air triggers the sensitization process. Sensitization looks less occur in 304 stainless steel welds which were rapidly cooled in oil.

Abstract: Austenitic stainless steel is susceptible to sensitization when exposed to high temperatures. During welding operations, they tend to form chromium depletion zones and thus become susceptible to intergranular corrosion. The microstructure and hardness properties of AISI 321 austenitic stainless steel welds have been studied in this work. The phenomenon of sensitization of AISI 321 stainless steel during GTAW has also been investigated. This experiment observed three welded samples using different filler metals, ER316, ER308, and ER347. Weld sample analysis was studied using an optical microscope and a microhardness tester. The results demonstrated that the type of filler metal significantly affected changes in the microstructure and hardness of the weld joint.

Abstract: In this paper, 347H stainless steel of three situation of solution, primary and secondary stabilizing with 0, 12, 24, 48 and 72 h accelerated sensitization heat treatment. The change of sensitization degree with time was studied by metallographic test, double-loop electrochemical potentiodynamic reactivation (DL-EPR) test, intergranular corrosion test and microscopic morphology observation. The result shows that the sensitization degree of the solution material increases rapidly and reaches the maximum value after 12h sensitization heat treatment. After that, it still belonged to severe sensitization situation, but the index gradually decreased. After stabilizing heat treatment, the sensitization degree of the material is lower than the situation of solution. After heat treatment for 48h, the material located on “possible sensitization” range, and the sensitization degree of the secondary stabilized material was always lower than is of the primary. It indicates that the sensitization of materials can not be completely inhibited by stabilizing heat treatment, and other anti-corrosion measures should be considered.

Abstract: Is the concern with latent phenomenon of sensitization, as it exposes austenitic stainless steels to one of the most severe types of corrosion, intergranular, caused by chrome impoverishment in some regions after the material has been treated thermally in a temperature range between 450°C and 850°C. The aim of this study is to identify the conditions under which the stainless steel AISI 304 austenitic will sensitize, microstructural analysis and reactivation potentiodynamics technique by Double cycle method (DL-EPR). In steel samples were subjected to different ranges of time and temperature. The behavior of the degree of sentiment reveals that the rainfall happens so intense under the conditions under study with the exception of 900oC - 1, 2, and 6, which was observed and proven both by microstructural analysis and the DL-EPR.

Abstract: Austenitic stainless steels always failure in intergranular corrosion, stress corrosion cracking and their synthesis. Moreover, hydrogen also plays an important role in SCC. Effects of sensitization and hydrogen on stress corrosion cracking of 18-8 type stainless steel (304 and 304L) were investigated in this paper. Three states of specimens, including as-received, sensitization and hydrogen precharged, were prepared for this study. Two kinds of environment, involving air and 0.5mol H₂SO₄ +0.01mol KSCN solution, were selected to compare the SCC sensitivity of different condition of 304 and 304L by the slow strain rate tensile test (SSRT). Fracture morphology was observed by scanning electron microscope (SEM) to check the SCC fracture characteristic. In SEM, evident secondary cracks were found on the fracture surface of 304. Results showed that: 1) hydrogen precharged 304L has high SCC sensitivity (85.7% ) compared with low SCC sensitivity in solution (14.5%), which reveal that SCC of 304L is hydrogen-induced cracking type; 2) 304 stainless steel has high SCC sensitivity (60.8%); 3) sensitization increases the SCC sensitivity of 304 stainless steel (from 60.8% to 71.4%).

Abstract: The aim of this study is to investigate the effect of cryogenic treated electrodes on the sensitization of ‘304 SS’ in resistance spot welding (RSW). An approach to model sensitization based upon the weld properties like: hardness, tensile-shear strength (T-S), while RSW of 304SS has been proposed and applied. Relationship between hardness, T-S and other parameter has been deduced by using Taguchi L9 orthogonal array (OA). The results indicate that for sensitization; coolant flow rate (CFR), weld time and voltage contributes significantly in RSW of SS.

Abstract: Chromium depletion in AISI304 stainless steel can lead to intergranular corrosion due to temperature conditions and degree of deformation, and consequently to materials failure. The aim of this work is to study the effect of sensitization treatment on the corrosion resistance in AISI304 stainless steel after solution heat treatment at 1,000°C. Sensitization treatments were carried out at 670°C for 1 h, 2h, 5h and 10h in the electrical furnace. The intergranular corrosion resistance of the sensitized specimens was evaluated by double loop electrochemical potentiokinetic reactivation test. The microstructure of the specimens before and after the corrosion tests was observed through optical and scanning electron microscope. Solution treatment shows the dual structure, however, aging for 5 hours depicts the ditch structure. The ratio of current density increased as a function of aging time resulted in increase in the degree of sensitization.

Abstract: The novel photocatalyst (FeTCPP-SSA-TiO₂) with chemical bond linking sensitized was successfully designed and fabricated. As bridging unite, sulfosalicylic acid (SSA) was used for grafting active functional groups onto TiO₂ surface thereby improving the adhesion strength between trtra-carboxyphenyl porphyrin iron (FeTCPP) and TiO₂. The morphology and structure of the photocatalyst was characterized. Finally, photocatalytic properties of the prepared samples have been investigated by the degradation of methylene blue (MB). The results indicated that FeTCPP-SSA-TiO₂ possessed enhanced photocatalytic performance and long-term stability over four recycles.

Abstract: Stainless steel (SS) is sensitized by thermal treatment in the range of 450°C to 800°C and inter-granular attack would occur upon subsequent exposure to certain media. This study is focused on modelling the effect of sensitization (by taking into consideration hardness as the weld property) in resistance spot welding (RSW) of 304SS, before and after cryogenic treatment on tungsten electrode. In the present work, outcome of Taguchi model has been used for developing a mathematical model for sensitization; using Buckingham’s π-theorem. The parameters of significance are coolant flow rate (CFR), voltage and time. This study will provide main effects of these variables on hardness of weld joint and will shed light on the sensitization mechanism in RSW of 304SS. The comparison with experimental results will also serve as further validation of model.