Papers by Keyword: Austenitic Steel

Abstract: The technology of diffusion saturation of austenitic steels by chromium and nickel in the medium of low-melting liquid metal melts is shown. The saturation temperature was up to 1050°C, and the duration was up to 8 hours. It was found that it is the most effective to apply coatings according to the technological scheme: pre-carburization-diffusion metallization – final carburization. It was found that the coating consists of 4 layers. The surface layer has a thickness of up to 5 mkm and a microtuberance of up to 19500 MPa. The second layer, up to 12 mkm thick, has a microhardness of up to 7500 MPa. The third, up to 50 mkm thick, has a microhardness of 2300 MPa. In the fourth layer, up to 150 mkm thick, the microhardness gradually decreases from 2300 MPa to the microhardness of the base. At the same time, the total thickness of the coatings is up to 200 mkm.

Abstract: Radiation porosity through-thickness of the fuel pin cladding, made of 16Cr-19Ni-2Mo-2Mn-Nb-Ti-V-P-B steel, has been studied with scanning electron microscopy using backscattered electron (BSE) detector. The examined sample was irradiated at a temperature around 480 °С up to an integral damage dose of 87 dpa. It was shown that, due to the temperature gradient through the cladding thickness, the average size of radiation voids reduces, and their concentration increases from internal to external surface. Local nonuniformity of radiation porosity is observed in regions close to internal and external surfaces. It was shown that, non-uniformity of radiation porosity is determined by the material structure, microtwin density and high concentration of low-angle inter-granular boundaries, in particular.

Abstract: One of ways to increase the strength of a structural material is to grind its microstructure to an ultra-fine-grained state. But with the simultaneous increase in strength properties in ultrafine materials, there is an inevitable decrease in its plastic properties. The use of metal materials with a gradient structure is an effective way to solve the problem of increasing the plasticity of metal products in general. This work is devoted to the study of the possibility of a gradient structure forming in austenitic stainless steel AISI-321 using radial-shear rolling. The results of the studies showed that the UFG-structure extends in the bar from its surface to a depth of at least a quarter of the radius of the bar. The transition zone is in the region between 0.5 R and 0.25 R of the bar section. Anything deeper is rolling texture. Due to the structural heterogeneity of the cross-section of the bar, there is a smooth drop in the micro-hardness of the central zone of the bar by 10.2 %. All this testifies to the gradient character of the structure formed in bars of AISI-321 steel deformed on the radial-shear rolling mill.

Abstract: This study investigates the effect of thermal aging on the microstructure and tensile properties of a 15-15Ti austenitic stainless steel in the baseline operating conditions of a sodium fast reactor, in the range between 400°C and 600°C. Samples that were aged at up to 600°C for 1000 hours exhibit no evidence of material recovery. Thus, after aging heat treatments, micro-hardness measurements do not decrease, and TEM analyses do not show any modification of the dislocation network. However, TEM examinations have indicated a new threshold for the precipitation of nanometric titanium carbides after an isothermal treatment at 500°C for about 5000 hours. Concerning the tensile properties, the aged states present a gain both in strength and in ductility compared to the initial cold-worked state. The large gain in ductility is observed for all of the temperatures tested (between 20°C and 400°C) and occurs concomitantly with an increase in the strain hardening rate of the material. One plausible hypothesis to explain this improvement of the mechanical behaviour relies on the nanometric titanium carbides formed during the aging process. These precipitates could act as obstacles that impede the motion of existing dislocations, thereby contributing an additional strain hardening mechanism, which would lead to greater strength and also delay the onset of strain localization.

Abstract: Austenitic stainless steels are widely used in industry. Increased requirements for the quality of products from these steel grades, the difficulties associated with the implementation of technological processes, as well as the high cost of steel, determine the necessity to assess probable causes of defects. This article presents an analysis of the influence of main process parameters on the quality of products from the grade 08X18H10T steel. Based on the results of statistical analysis and thermodynamic modeling, it was concluded that the increased content of titanium and nitrogen affects the quality of products, which is caused by the formation of titanium carbonitrides in the process of steel solidification.

Abstract: Due to the increasing of the price of different materials and resource saving it is very promising to develop technology of creation cheap coatings with specified properties. We developed a diffusion-doped powder based on austenitic steels for producing plasma-sprayed coatings. In comparison with Ni-based powders our materials have better adhesion, they are cheaper, they have better mechanical machinability, it is possible to produce coatings with required properties. In our work, the features of diffusion doping of microparticles of powder, the behavior of the powder in the plasma jet were studied. The significant decreasing of porosity, increasing of adhesion of the plasma-sprayed coatings after laser processing were marked. The substantial increase of wear-resistance in 2,5-3,0 times in comparison with untreated coatings when working in conditions of abrasive wear and atmospheric precipitation was revealed.

Abstract: Investigations conducted by transmission electron microscopy on thin foils were aimed at studying the structural-phase state of heat-affected zone of the welding joint performed by modulated current at two welding modes: coarse-droplet and fine-droplet transfer. Welding was conducted on the austenitic steel 0.12С-18Cr-10Ni-1Ti-Fe using the facility UDI-203. Welding modes were: I_i = 175 А (coarse-droplet transfer) and 140 А (fine-droplet transfer). Welding was performed on thin foils sized 200 × 15 × 4 mm³. Investigations were focused on heat-affected zone at the distance of 1 mm from the weld line towards the base metal – the base metal zone and at the distance of 0.5 mm towards the welded metal – the welded metal zone. The studies showed that in the state before welding the steel matrix presents γ-phase (austenite), which has face-centered cubic (fcc) crystal lattice. Morphologically the steel structure is given as grains where defect structure is presented by only network dislocation substructure, and grains where along with the dislocation substructure there are mechanical (or deformation) microtwins in the form of packages of one, two and three systems. It was established that welding of steel 0.12С-18Cr-10Ni-1Ti-Fe by modulated current with coarse-droplet transfer leads to martensitic transformation γ → ε only in the welded metal zone. At fine-droplet transfer welding leads to martensitic transformation γ → ε both in the base metal zone and in the welded metal zone. In the welded metal zone phase transformation γ → ε occurs more intensively. It was revealed that crystal lattice distortion in the whole heat-affected zone at welding by modulated current has only plastic nature, irrespective of the welding mode. Welding by modulated current with fine-droplet transfer leads to lower internal stresses in the whole heat-affected zone.

Abstract: The paper presents the results of a study of the lanthanum hexaboride nanosized powder modification effect on the cast structure of martensitic and austenitic steels deoxidized with aluminum and silicon. The study was conducted on high-chromium steels of austenitic and martensitic classes, and nanosized lanthanum hexaboride powder was used as a modifier. Studies of the chemical composition of the obtained samples, qualitative and quantitative analysis of non-metallic inclusions, the structure of the steel and thermodynamic modeling were carried out.

Abstract: This article presents the results of a study of martensitic steels. Studied steels: OZH9K14N6MZD, 12X18N10TL, 07X13G28ANFL. The object of the study was the optimization of properties for use in cryogenic technology. The purpose of the study is to increase the strength and service life of products for various purposes. The destruction of steel 12X18N10TL and 07X13G28ANFL was investigated. It has been established that 07X13G28ANFL steel is more preferable for cryogenic use and is recommended by the authors.

Abstract: Different mesostructural elements of 16Cr-19Ni-2Mo-2Mn-Nb-Ti-B austenitic steel have been examined after neutron irradiation to damage dose up to 82 dpa by scanning electron microscopy using orientation microscopy (EBSD). Radiation porosity with maximum void size up to 200 nm was observed in austenitic steel structure after neutron irradiation. Nonuniformity, related to mesostructural elements, such as general grain boundaries, special CSL boundaries Σ3 (twins), areas with high density of low-angle boundaries, is typical for radiation porosity.