Papers by Keyword: Intergranular Corrosion

Abstract: During the study of laser cladding processes for manufacturing of structural elements from high-alloy corrosion-resistant steel on a thin-walled base, the issue of reduction of the powder material corrosion durability, applied by such technologies, during their use in corrosive environments, was considered. The aim of this study is to determine the effect of laser radiation intensity, used to form a deposited layer on a thin-walled base made from AISI 316L high-alloy corrosion-resistant steel, on its corrosion resistance. Samples, utilizing a laser cladding method, developed for creation of structural elements on pre-made thin-walled parts, were tested for pitting and intergranular corrosion (IGC) resistance using standard methods. IGC resistance was assessed by optical metallography. According to the results of corrosion tests, it was determined that samples of the layers of high-alloy corrosion-resistant steel AISI 316L, applied utilizing laser cladding technology on a thin-walled base, made from high-alloy corrosion-resistant steel, can be considered resistant to pitting and intergranular corrosion, while maintaining the range of values of power density at 30...50.0 kW/cm². These results align with the results of various studies by other authors who have been testing similar cases in other industries. The results of this study were used for further development of laser surfacing technologies for thin-walled parts used in various extreme conditions and further deepening of knowledge about modern laser cladding processes and expansion of the scope of this technology.

Abstract: Stainless steels are the material that has chromium as a main component. The chromium content reacts with oxygen in air, subsequently, forms thin chromium oxide film on the surface of stainless steels. Thus, when these steels are exposed to high temperature for a long period of time in many applications, chromium carbide could precipitate along the grain boundary and reduce the corrosion resistance. This project is conducted to study annealing time effect on stainless steels when exposed to high temperature at various exposure time periods. Three different kind of stainless steels, namely, AISI 304, AISI 304D and AISI 2205 were used in this study. Stainless steels were heated at 600°C for 0, 6, 24, 48 and 96 hours, then cool down in air. Consequently, the investigations were performed by using double-loop Electrochemical Potentiokinetic Reactivation (DL-EPR) and Cyclic Potentiodynamic Polarization (CPP) to study degree of sensitization and film properties. In addition, chromic acid and oxalic acid were used as reagent of acid etching to observe microstructures. Finally, Vickers hardness test were also conducted. Percentage degree of sensitization increased from 2.93% to 62.20% in AISI 304, increased from 5.26% to 55.54% in AISI 304D and from 12.19% to 69.35% in AISI 2205. The pitting potential decreased from 0.47 mV to 0.23 mV for AISI 304 but remained relatively constant for AISI 304D and AISI 2205. The results indicated that after the specimens were exposed to high temperature for a long period of time, all specimens had more chromium depleted areas, more carbide along the grain boundaries, worse film quality and small changes in hardness value.

Abstract: Heat exchangers are widely used in the industry for processing natural gas. The article discusses the causes of corrosion damage to the internal surface of the stainless steel tubes for the heat exchanger coil. Chemical composition of tubes was obtained for provided damaged batch. Results of metallographic studies, as well as results of scanning electron microscopy of individual parts of pipes are presented. Tests for resistance to intergranular corrosion were carried out. The study revealed that the main reason of corrosion damage on the inner wall of the tubes is the formation of carbides along the boundaries of austenitic grains, and as a result, the chromium-depleted grain was subjected to corrosion.

Abstract: In this paper, the simulated welding structure at different areas of heat affected zone (HAZ) of austenitic stainless steel are prepared by heating furnace, and the deference of intergranular corrosion resistance of all samples were determined by comparative methods of oxalic acid etching, hot-acid test and electrochemical potentiodynamic reactivation tests (EPR), and the effectiveness of all those methods were analysis and determination at the same time. The result shows that the susceptibility degree at different areas of HAZ increased with the heating temperature increase, but all structures can pass hot-acid test and EPR test, indicating that it could maintain good performance of intergranular corrosion resistance. The hot-acid test results have good consistency with EPR test , but inconsistent with oxalic acid etching test. The results show that the evaluation of oxalic acid etching is too much strict to be used as a judgment method, so that not suitable of use for inspection.

Abstract: This article presents the results of experimental studies of the effect of processing conditions on the corrosion resistance of polished parts made of stainless chromium-nickel steel of austenite class 12X18N10T. It is established that the introduction of the ultrasonic field energy into the shaping zone during grinding can increase the corrosion resistance of parts by 12-15 %, depending on the elements of the grinding mode. The latter is explained by a significantly lower heat-force stress during processing, which, in turn, leads to a decrease in the magnitude and depth of distribution of technological residual tensile stresses along the surface layer.

Abstract: The reasons for the decrease in the operational resistance of high-pressure metal hoses made of austenitic steels are considered. The main cause of damage to metal high-pressure hoses was revealed, namely, the low performance of the metal protective braiding under the influence of an unfavorable environment. It has been established in the work that in the initial state the wire made of AISI 201 steel has a high strength (σ_0.2 = 1370 MPa and σ_T = 1650 MPa) and has relatively low plastic characteristics (δ = 15 % и ψ = 40 %), since up to 40–60% deformation martensite is present in its structure. The resistance of steels of the austenitic class AISI 201 and AISI 316 to intergranular corrosion has been investigated. The effect of heat treatment on the mechanical and plastic properties of wire samples of ø made of AISI 201 steel has been investigated. Optimal heat treatment modes have been determined that increase the durability of the braid in an unfavorable environment and, consequently, the operational durability of metal hoses in general.

Abstract: The effects of two-stage aging on the microstructures, tensile properties and intergranular corrosion (IGC) sensitivity of Al-Mg-Si alloys were studied by tensile testing and IGC experiments and transmission electron microscope (TEM). The results show that the two-stage aging (180°C, 2h+160°C, 120h) can reduce the IGC sensitivity without decrease the tensile properties. The grain is distributed with high-density β′′ phases, and the grain boundary phases are spherical and intermittently distributed. The formation of the microstructure characteristic is due to the lower re-aging temperature, which results in a decline differences in the diffusion rate between the matrix and grain boundaries. As a result, the pre-precipitated phase can maintain a better strengthening effects due to the slower growth rate. The pre-precipitated phase of the grain boundary presents a spherical and intermittent distribution due to the fast coarsening speed.

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: In this study, the mechanical properties and intergranular corrosion properties of 347H austenitic stainless steel were studied by tensile test, impact test, double-ring electrochemical potentiodynamic reactivation test (DL-EPR) and microstructure observation in three states of solution, primary and twice stabilized state. Results showed that the key mechanical properties of 347H stainless steel under three different conditions had little change, and the mechanical properties at room temperature were not affected by the stabilizing heat treatment. After 12h of sensitization, the solution material showed obvious sensitization behavior, and the Ir/Ia index exceeded 0.3, indicating that the material entered the range of complete sensitization. Both primary and twice stabilizing heat treatment can significantly reduce the occurrence time of sensitization and prevent the sensitization process. However, the stabilizing heat treatment cannot completely prevent the material sensitization, and it must be combined with other methods .

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.