Papers by Keyword: Thermomechanical Treatment

Abstract: Shape setting is a particular thermo-mechanical process used to imprint the desired shape in Nitinol (NiTi) shape memory alloy semi-finished products. It is a critical step as it must simultaneously ensure precise shape definition and specific transformation temperatures (TTs), on which the achievement of functional properties is based. Once a shape setting treatment has been optimized, it becomes highly relevant in industrial production to assess whether the same parameters can be applied to components with different geometries, therefore involving different mold designs. This study investigates the influence of mold geometry on the TTs of NiTi tubes, shape set to obtain different kinds of annuloplasty rings. Starting from the same tube batch and applying identical heat treatment parameters, two mold designs were used to impart different shapes and the phase transformation behavior was investigated. The results show that mold geometry does not significantly affect the TTs, indicating that the same shape setting parameters can be applied across different component geometries.

Abstract: In order to increase strength while maintaining the ductility of material, pure titanium was improved through the thermomechanical treatment that combines rolling and heat treatment. The tensile properties of pure titanium treated by rolling and heating were investigated. Test material was JIS Grade 2. This material has a higher corrosion resistance. However, the strength of JIS Grade 2 is lower than that of JIS Grade 3. JIS Grade 2 with high strength while maintaining corrosion resistance is being developed. Techniques for improving the properties of materials with simple compositions are important. Thermomechanical treatment is used as a method for improving material properties. In the present study, the effect of thermomechanical treatment on the material properties of JIS Grade 2 was investigated. Rolling was performed at room temperature and the reduction ratio ranged from 70 to 90 %. The heating temperature was in the range of 300 to 700 °C. Heat treatment from 400 to 500 °C showed an increase in tensile strength while maintaining ductility. When the heat treatment temperature was 450 °C, the strength and elongation were approximately 600 MPa and 25 %. Tensile stress of JIS Grade 4 and the tensile strain of JIS Grade 1 were exhibited.

Abstract: Two schemes of thermomechanical processing of F420W cold-resistant steel to produce sheets with thickness of 5 and 15 mm for manufacture of wind turbine towers, were developed and tested in laboratory conditions. The first scheme simulated hot rolling on a continuous mill, including reductions with minimal inter-deformation pauses and subsequent slow cooling. The second one corresponded to hot rolling on a reverse mill with accelerated cooling. Mechanical properties were analyzed taking into account the related structural features. Technological recommendations for hot rolling of a thin sheet made of high-strength cold-resistant steel were proposed.

Abstract: The results of tests for resistance to abrasive wear on highly abrasive hard rock white electrocorundum are presented. The main material of fast-wearing elements of mining and processing equipment-110G13L steel (Gadfield steel) in comparison with other 9 grades of steel and cast iron, including specially developed wear-resistant foreign steels such as Hardox and Miiluks, is analyzed. The studies were carried out using an experimental stand for studying the material wearing process. On the stand the sample was fixed in a holding device and, after being brought into contact with the abrasive, it was rotated under a constant load. As a result of the experiments, it was confirmed that the order of placement of the tested materials in terms of increasing wear resistance coincides with their placement in terms of increasing hardness. At the same time, the wear resistance of the most resistant material – U8A steel after quenching – is about 4 times higher than this indicator for the least resistant components – low-carbon steel 25L, including gray and high-strength cast iron SCH21, VCH35. The wear resistance of 110G13L steel, as well as 65G, U8 steels in the hardened state, is from 1.5 to 2 times higher than that of foreign steels M400, H450, M500, H500. The results of the conducted studies allow us to evaluate the analyzed materials on the basis of their wear resistance and hardness indicators on the feasibility of using them in the manufacture of fast-wearing parts of mining equipment. Based on the research data, it seems promising to develop new ways to increase the wear resistance of domestic steel, including 110G13L steel traditionally used in mining.

Abstract: The article investigates the effect of the strain rate on the driving force of recrystallization during hot working of the as-cast structure. For the study, we applied previously obtained experimental data of recrystallization kinetics during this stage of thermomechanical treatment. In addition, hot laboratory rolling, followed by saltpeter bath soaking, were performed in order to obtain supplemental data on grain structure size and orientations. Grain structure size was examined by optical microscopy, and its orientation was examined by X-ray texture analysis. The studies demonstrated, that overestimated recrystallization driving force not only results in erroneous kinetics estimation, but also gives excessive number of recrystallization centers and undersized grain structure. Besides, unaccounted effect of recrystallization driving force on grain size leads to distorted predictions of texture composition. In order to avoid this, it was recommended to apply an special exponential accumulated strain dependent coefficient.

Abstract: Microstructural evolution during the strain-induced phase transformation of austenite in an Austempered ductile iron (ADI) under various thermomechanical processing conditions is studied in the present study. An alloyed ductile iron is taken as the base material, and thermomechanical treatment is carried out on a Gleeble 3800 thermomechanical simulator coupled with dilatometry. The effect of deformation on the austempering process has been studied by microstructure characterization using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. The variations in retained austenite volume fraction and its carbon content with respect to different austempering times are analyzed to study the effect of strain-induced transformation of austenite. It has been observed that the thermomechanical treatment significantly influences the phase transformation kinetics during the austempering process. The thermomechanical treatment produced a martensite free ausferritic microstructure for all austempering times with a high volume fraction of carbon enriched retained austenite as compared to the conventional heat treatment.

Abstract: On the thermomechanical treatments of Cu-Ni-Si alloy, cold-rolling (CR) before solution heat treatment (SHT) is commonly conducted to eliminate defects in a casting slab. In addition, a rolling is applied to reduce/adjust the thickness of casting slab before SHT. In a heavily deformed microstructure by CR, on the other hand, grain growth during a heating in SHT is likely to occur as the result of recrystallization. In general, tensile strength and fatigue strength tend to decrease with an increase in the grain size. However, the effect of difference in grain sizes produced by with and without CR before SHT on the fatigue strength is unclear. In the present study, fatigue tests of Cu-6Ni-Si alloy smooth specimens with a grain fabricated through different thermomechanical processes were conducted. The fatigue behavior of Cu-Ni-Si alloy was discussed.

Abstract: In Europe EUROFER 97 has been recognised as reference steel for the nuclear costructions under high radiation density for first wall of a fast breeder reactors as well as in other high stressed primary structures such as the divertors, blanklet and vessels. Following to this a EUROFER 97 detailed knowledge of the microstructure evolution after thermo-mechanical processing is required, because the material mechanical properties are interesting also for innovative solar plants, i.e. NEXTOWER project. A detailed knowledge of process optimisation is mandatory because EUROFER 97 steel mechanical properties and microstruture are heavily influenced and improved (and easily affeted) by thermomechanical treatments. In this paper the effect of thermo-mechanical parameters on the grain refinement of EUROFER 97 has been investigated by cold rolling and heat treatment on pilot scale.

Abstract: The article deals with the strength of adhesion of coatings with the parts of type «shaft». In accordance with the above separation, gas-thermal methods of spraying and thermal power sintering have an adhesive interaction of particles and coatings. The use of thermomechanical treatment of preformed coatings (applied by thermal spraying) makes it possible to increase the adhesion strength of coatings with parts of «shaft» type. For a quantitative assessment of the adhesion strength of coatings with the base metal, a shear coating method was used. An experiment to determine the adhesion strength of samples of steel with various applied coatings is considered. It was concluded that the adhesion strength of the coatings obtained using the hydrogen-propane mixture was slightly superior.

Abstract: Recently, the use of high temperature materials are became more common in different types of engineering activities. The new generation of Oxide dispersion strengthened alloys (ODS) consist of Fe-Al matrix with small oxide particles dispersed within it, was generated by the authors to keep their mechanical properties at elevated temperatures. The new ODS prepared by means of mechanical alloying and hot consolidation. The preliminary tests results shows a better oxidation resistant, creep and Ultimate Tensile Strength (UTS) compare to similar materials. To go more inside in thermomechanical and microstructural properties, a series of different test were performed on different variant of ODS which manufactured by the authors. The results show that the annealing time and temperature has a significant influence on these properties while almost total recrystallization of grains and subgrains were observed during the investigation.