Microstructure and mechanical properties of C-Si-Mn(-Nb) TRIP steels after simulated thermomechanical processing

Continuous and discontinuous cooling tests were performed using a quench deformation dilatometer to develop a comprehensive understanding of the structural and kinetic aspects of the bainite transformation in low carbon TRIP (transformation induced plasticity) steels as a function of thermomechanical processing and composition. Deformation in the unrecrystallised austenite region refined the ferrite grain size and increased the ferrite and bainite transformation temperatures for cooling rates from 10 to 90 K s-1. The influence of niobium on the transformation kinetics was also investigated. Niobium increases the ferrite start transformation temperature, refines the ferrite microstructure, and stimulates the formation of acicular ferrite. The effect of the bainite isothermal transformation temperature on the final microstructure of steels with and without a small addition of niobium was studied. Niobium promotes the formation of stable retained austenite, which influences the mechanical properties of TRIP steels. The optimum mechanical properties were obtained after isothermal holding at 400&deg;C in the niobium steel containing the maximum volume fraction of retained austenite with acicular ferrite as the predominant second phase.<br /

Atomic observations of warm rolled low carbon steels alloyed with Cr and P

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 200

Microstructure and mechanical properties of thermomechanically processed C-Si-Mn steels

Comparison of the microstructures formed in the specimens produced by corresponding schedules in the dilatometer and by laboratory rolling has shown that a higher level of retained austenite was achieved in dilatometer specimens, whereas in rolled specimens a higher amount of martensite was present instead of retained austenite

Recent progress on the study of the microstructure and mechanical properties of ECAE copper

Results on the microstructure and the tensile properties of equal channel angular extruded (ECAE) copper processed for one to 16 passes are presented and compared with the available literature data. With increasing number of passes (N), the microstructure changes from a strongly elongated shear band structure after N=1 and 2, towards a more equiaxed subgrain and grain structure. This is accompanied by a decrease in the cell wall or subgrain-boundary widths and an increase in recovered or even recrystallised grain structures with low dislocation densities. Electron backscatter diffraction measurements have indicated that for lower N, the location of Σ3 boundaries is restricted to shear bands, while at greater N, Σ3 boundaries were found to be more widely distributed. Texture measurements indicate close similarity with simple shear texture components and a spread of the orientation components with greater N. Upon comparing the tensile behaviour of as-ECAE Cu with the surveyed literature, broad agreement on the strength of the material is achieved. However, a strong variation in the percentage elongation to failure is also noted. Strain hardening and deformation kinetic analysis via strain rate jump tests indicate an evolution from stage III to V hardening during post-ECAE compression and a saturation in the strain rate sensitivity after N=4 resulting in maximum values of ∼0.02. Our results suggest that rather than a change in deformation mechanism, the increase in ductility with increasing N is associated with an increase in the mean free path of dislocations—with the grain boundaries remaining actively involved as the transmitter of plastic strain and their interaction with dislocations being the rate controlling deformation mechanis

Експериментальна перевірка ефективності методики навчання майбутніх філологів фонетики китайської мови

The processes of globalization and the world community, as well as the role and place of Ukraine and the People's Republic of China on the geopolitical map of the world dictate the need for strong scientific, political, economic, cultural, energy contacts that will lead to the progress of both countries, to the creation and development of new technologies, new economic and humanitarian relations. This requires the training of a large number of skilled Chinese language specialists and experts.The phonetics of the Chinese language is extremely important for the learning of the language as a whole, because the Chinese language has a special typological characteristic - the presence of a tone that performs distinctive-perceptual and distinctive-significative functions. Mastering Chinese, and in particular lexical units (as key in communication), can only be conditioned by the ability to distinguish and correctly reproduce a tone. However, the study of phonetics is not limited to articulation skills, but involves the students mastering rhythmic-intonational models, which also have semantic nuances and are important in terms of the implementation of speech pragmatics.The study describes the experimental verification of the effectiveness of teaching methods of future philologists of Chinese phonetics, as well as substantiates and confirms the choice of the study hypothesis. The criteria and norms for evaluating the Chinese linguistic phonetic competence of future synologists are outlined. Methods and materials, plan and structure, and duration of the experiment are determined. In addition, examples of tasks and the ultimate goal of their implementation were given.Organizational and content aspects of students' experimental learning are covered. Post-experimental sections were performed, the corresponding results of the effectiveness of the created methodology of teaching phonetics of Chinese language were presented. For clearer perception, the results of the sections were made in the tableПроцессы глобализации и мирового содружества, а также роль и место Украины и Китайской Народной Республики на геополитической карте мира диктуют потребность в создании прочных научных, политических, экономических, культурных, энергетических контактов, которые приведут к прогрессу обеих стран, к созданию и развитию новых технологий, новых экономических и гуманитарных отношений. Это требует подготовки большого количества квалифицированных специалистов и знатоков китайского языка.Фонетика китайского языка является крайне важной для обучения языку в целом, ведь китайский язык имеет особую типологическую характеристику - наличие тона, который выполняет дистинктивно-перцептивную и дистинктивно-сигнификативную функции. Овладеть китайским языком и в частности лексическими единицами (как ключевыми в общении) можно только при условии способности различать и правильно воспроизводить тона. Однако изучение фонетики не ограничивается артикуляционными навыками, а предполагает усвоение студентами ритмико-интонационных моделей, которые так же имеют семантические оттенки и важны в плане реализации прагматики речи.В исследовании описана экспериментальная проверка эффективности методики обучения будущих филологов фонетики китайского языка, а также обоснованно и подтверждено выбор гипотезы исследования. Указано критерии и нормы оценки фонетической компетентности китайского языка будущих филологов-синологов. Определены методы и материалы, план и структура, а также продолжительность эксперимента. Кроме того были приведены примеры задач и конечная цель их выполнения.Освещены организационные и содержательные аспекты экспериментального обучения студентов. Проведены послеэкспериментальные срезы, изложенные соответствующие результаты эффективности созданной методики обучения фонетике китайского языка. Для более четкого восприятия результаты срезов были вынесены в таблицеПроцеси глобалізації та світової співдружності, а також роль і місце України та Китайської Народної Республіки на геополітичній карті світу диктують потребу у створенні міцних наукових, політичних, економічних, культурних, енергетичних контактів, які призведуть до поступу обох країн, до створення та розвитку нових технологій, нових економічних та гуманітарних відносин. Це потребує підготовки значної кількості кваліфікованих фахівців та знавців китайської мови.Фонетика китайської мови є вкрай важливою для навчання мови в цілому, адже китайська мова має особливу типологічну характеристику – наявність тону, який виконує дистинктивно-перцептивну та дистинктивно-сигніфікативну функції. Оволодіти китайською мовою та зокрема лексичними одиницями (як ключовими в спілкуванні) можна лише за умови здатності розрізнювати та правильно відтворювати тони. Проте вивчення фонетики не обмежується артикуляційними навичками, а передбачає засвоєння студентами ритміко-інтонаційних моделей, які так само мають семантичні відтінки і є важливими в плані реалізації прагматики мовлення.У дослідженні описана експериментальна перевірка ефективності методики навчання майбутніх філологів фонетики китайської мови, а також обґрунтовано та підтверджено вибір гіпотези дослідження. Зазначено критерії та норми оцінювання китаємовної фонетичної компетентності майбутніх філологів-синологів. Визначено методи та матеріали, план та структура, а також тривалість експерименту. Крім того були наведені приклади завдань та кінцева мета їх виконання.Висвітлено організаційні і змістові аспекти експериментального навчання студентів. Проведені післяекспериментальні зрізи, викладені відповідні результати ефективності створеної методики навчання фонетики китайської мови. Для більш чіткого сприйняття результати зрізів були винесені в таблиц

Grain Size, Misorientation, and Texture Evolution of Copper Processed by Equal Channel Angular Extrusion and the Validity of the Hall-Petch Relationship

The microstructure and texture of copper subjected to equal channel angular extrusion (ECAE) via route B C for up to 16 passes have been assessed using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction (XRD) peak broadening, and texture analysis. The differences in grain size measured by these techniques allows for an understanding of microstructural evolution. A gradual decrease in grain size occurs with an increasing number of passes, while the subgrain size remains approximately constant. Up to four passes, the fraction of high-angle grain boundaries (HAGBs) (>15 deg) increases from 15 to 45pct, but remains constant thereafter. The grain boundary character distribution shows a decrease of Σ1 boundaries and an increase of Σ3 boundaries with higher passes. After 16 passes, a few regions of large 1 to 4 μm sized grains embedded in a submicrometer sized matrix were observed. These agglomerates of larger grain diameters together with the measured decrease in the dislocation density correlate with the observed decrease in yield strength of samples subjected to four and more passes. Texture evolution is adequately described under conditions of negative simple shear. The effect of increased accumulated strain results in an overall spread of orientation densities due to the absence of stable end positions post-ECAE. Detailed microstructural information suggests that strengthening mechanisms in the material can be sufficiently well described by the classical Hall-Petch relationship by applying it to the subgrain size, while the subgrain size remains smaller than the grain siz

Effect of holding temperature and time on ferrite formation in dual phase steel produced by strip casting

Conventional dual phase (DP) steel (0.08C-0.81Si-1.47Mn-0.03Al, wt. %) was manufactured by the laboratory simulation of strip casting. The effect of holding temperature and time on microstructure evolution was studied using a quench-deformation dilatometer. Microstructures were observed using optical and scanning electron microscopy. The results showed that the nose temperature of ferrite phase field is around 650 °C. The kinetics of ferrite formation is fast within the first 100 s of holding at this temperature, and then formation of ferrite continues at a slower rate until it reaches the fraction corresponding to that defined by the lever rule. 70~80 % ferrite was obtained after holding at 650 °C for 100~900 s. Some Widmänstatten ferrite was also observed probably because of a large prior austenite grain size and quenching after holding. In addition, austenite-to-ferrite transformation kinetics is fitted well using Johnson-Mehl-Avrami equation. The Avrami exponent for ferrite formation was approximately 1 for both 650 and 670 °C holding temperatures, which means rapid ferrite transformation. It deduces that the ferrite formation obeys a linear growth behavior, which is associated with a decrease in amount of nucleation sites

Addressing retained austenite stability in advanced high strength steels

Advances in the development of new high strength steels have resulted in microstructures containing significant volume fractions of retained austenite. The transformation of retained austenite to martensite upon straining contributes towards improving the ductility. However, in order to gain from the above beneficial effect, the volume fraction, size, morphology and distribution of the retained austenite need to be controlled. In this regard, it is well known that carbon concentration in the retained austenite is responsible for its chemical stability, whereas its size and morphology determines its mechanical stability. Thus, to achieve the required mechanical properties, control of the processing parameters affecting the microstructure development is essential

Observation of Precipitation Evolution in Fe-Ni-Mn-Ti-Al Maraging Steel by Atom Probe Tomography

We describe the full decomposition sequence in an Fe-Ni-Mn-Ti-Al maraging steel during isothermal annealing at 550 °C. Following significant pre-precipitation clustering reactions within the supersaturated martensitic solid solution, (Ni,Fe)3Ti and (Ni,Fe)3(Al,Mn) precipitates eventually form after isothermal aging for ~60 seconds. The morphology of the (Ni,Fe)3Ti particles changes gradually during aging from predominantly plate-like to rod-like, and, importantly, Mn and Al were observed to segregate to these precipitate/matrix interfaces. The (Ni,Fe)3(Al,Mn) precipitates occurred at two main locations: uniformly within the matrix and at the periphery of the (Ni,Fe)3Ti particles. We relate this latter mode of precipitation to the Mn-Al segregation

Effect of mo, nb and v on hot deformation behaviour, microstructure and hardness of microalloyed steels

Three novel low carbon microalloyed steels with various additions of Mo, Nb and V were investigated after thermomechanical processing simulations designed to obtain ferrite-bainite microstructure. With the increase in microalloying element additions from the High V-to NbV-to MoNbV-microalloyed steel, the high temperature flow stresses increased. The MoNbV and NbV steels have shown a slightly higher non-recrystallization temperature (1000°C) than the High V steel (975°C) due to the solute drag from Nb and Mo atoms and austenite precipitation of Nb-rich particles. The ambient temperature microstructures of all steels consisted predominantly of polygonal ferrite with a small amount of granular bainite. Precipitation of Nb-and Mo-containing carbonitrides (\u3e20 nm size) was observed in the MoNbV and NbV steels, whereas only coarser (~40 nm) iron carbides were present in the High V steel. Finer grain size and larger granular bainite fraction resulted in a higher hardness of MoNbV steel (293 HV) compared to the NbV (265 HV) and High V (285 HV) steels