Papers by Keyword: Austenitic Steel

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: ECCC is a voluntary grouping formed in 1991 to co-ordinate Europe-wide development of creep data to be used to design components for high temperature plants, bases on a Memorandum of Understanding, signed by all partners. The ECCC is deeply involved in EU coordination for the development of knowledge on the damage caused by the creep phenomenon and the consequent reliability assessment activities. Strong links exist with the technical committees of the European Standard organizations, giving an efficient network to mutually exchange of technical information relating to current/future activities for the improvement or development of new materials. For several years ECCC (1991-2005) concentrated efforts by EU support. Nevertheless, revitalization of ECCC has been generated by definition of Joint Industrial Project (JIP) started in 2011 and still running (JIP4). ECCC has a very strong link to industrial applications and it is presently organized in four Work Packages: WG1 on common procedures, data generation/assessment and three material specific Working groups: ferritic steels, austenitic steels, nickel-based alloys. Two main outputs are ECCC data sheets and ECCC Recommendation Volumes. The ECCC activities are almost completely carried out by members’ contribution-in-kind. The ECCC plays a part of its role, in term of generation of design properties for new materials introduction into power plant and related applications. It therefore engages a crucial role in assessing and realising the potential of new developments.

Abstract: Austenitic stainless steels are commonly used for hydrogen storage and transportation. These alloys have a high nickel (Ni) content, which increases alloy cost. In this study, high manganese (Mn) austenitic alloys were evaluated as potential lower cost alternatives. Two heats of high Mn alloys with different stacking fault energies (SFE) of ~29 mJ·m^-2 and 49 mJ·m^-2 were acquired. Additionally, a new vanadium (V)-microalloyed high Mn alloy was designed to achieve a SFE of 47 mJ·m^-2 to minimize planar slip deformation mechanisms. Post-processing via cold working in conjunction with aging was also performed on the V-microalloyed high Mn steel. Hydrogen embrittlement sensitivity was investigated using circumferential notch tensile specimens cathodically charged with hydrogen in a 0.05M NaOH electrolytic solution. The alloys were compared to a cold-worked 316L stainless steel, which exhibited no strength loss due to hydrogen. The high Mn alloys with SFE of ~29 mJ·m² and 49 mJ·m^-2 had notch strength losses of 11 and 6 pct, respectively. The V-microalloyed high Mn steel in the as-hot-rolled condition had a notch strength loss of 17 pct. The V-microalloyed high Mn steel in the cold worked and aged condition indicated no notch strength loss in hydrogen, which was comparable to the performance of the 316L stainless steel.

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: The article is focused on the analysis of fracture mechanisms of specimens made of austenitic steel, which have been subjected to dynamic tests. Austenitic stainless steels are characterized as high corrosion resistant materials with high bio-tolerance and relatively high strength. They are made by cold working, where plastic deformation occurs and they are deformed especially by slipping and twinning. Deformed regions are characterized by deformation twins and slip deformation. Specimens were used in two states, in the initial state and after chemical-thermal treatment. Dynamic tests to which specimens were subjected were the impact test and the three-point bending test. Fracture areas were evaluated by scanning electron microscope.

Abstract: Stress-strain behavior of austenitic stainless steel grade AISI 304 was investigated by means of uniaxial tensile tests and magneto-phase analysis. The test materials were strained in tension within the temperature range of-100 ≤ T ≤ +100 °C. According to the results, intensive strain hardening occurs in austenitic stainless steel when strain-induced α’- martensite is present in the material, and stress-strain behavior is associated with the increase yield strength and tensile strength with decreasing temperature. The analysis of the hardening kinetics reveals that kinetics are affected by the temperature and by the amount of α’- martensite content.

Abstract: This work aims at investigating the stages and irregularity of plastic strain in austenitic stainless steel 12Kh18N9T within a temperature range of 143 < T < 420 K. The localized plastic strain fronts at different stages of strain hardening have been visualized and monitored via digital speckle photography (DSP). This method consists in the high-accuracy recording of the displacement field via tracking any material surface changes and the subsequent comparison of speckle images acquired under uniaxial tension. The stress-strain diagrams were found to strongly vary with a decrease in temperature due to strain-induced-phase transition. The analysis of localized strain distributions revealed the emergence of a mobile system of equidistant strain localization foci at the strain hardening stage. The temperature dependence of plastic strain localization parameters at the linear strain hardening stage was established as well.

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 paper presents the results of studies of a new cast high-strength austenitic corrosion-resistant steel, which can be successfully used in shipbuilding for the manufacture of fittings. The authors included data on the structural-phase state of steel, the results of evaluating the mechanical properties, wear and corrosion resistance of the metal of castings in the cast and heat-treated state. The mechanical properties of steel are considered in detail in a wide temperature range. The impact strength was considered at low temperatures and static strength at 20 to 350 ° C. It is shown that steel has higher mechanical and corrosive properties in a wide temperature range than those of traditional stainless steels. The corrosion resistance of steel is considered. This is intergranular and pitting corrosion; the main types of corrosion are peculiar for shipbuilding. It has been shown that cast steel is superior to traditional corrosion-resistant steels in pitting corrosion resistance estimated by the pitting coefficient PREN and the critical temperature of pitting. The new cast steel has the same wear resistance as Hadfield steel.

Abstract: In this paper, we consider the effect of cold rolling and hydrogen alloying on the formation of twin boundaries of the corrosion resistance of austenitic steel 01Cr17Ni13Mo3. Using the method of transmission electronic microscopy, microdiffraction patterns were obtained. The analysis of microdiffraction patterns indicates the formation of a developed grain-subgrain structure with small-angle and large-angle misorientation. The structure has a high dislocation density, deformation twins and localized shift bands. It was established that plastic deformation by flat rolling to ε = 90 % at room temperature does not contribute to the appearance of a noticeable amount of α' and ε-martensite. At the temperature of liquid nitrogen, the samples were found to form a small fraction of the α'-martensite phase. Such a small amount of martensite can contribute to steel strengthening, and a decrease in the rolling temperature will lead to an increase in the strength properties of steel. It was detected that the density of twin boundaries under the decrease in the rolling temperature but with the same intensity of hydrogen saturation is significantly higher. A noticeable reduction in the width of the twin lamellas was revealed.