Analysis of the microstructure development during rolling on the heavy section mill in Liberty Ostrava a.s.

Diplomová práce se zabývá analýzou vývoje mikrostruktury oceli S355J2 mikrolegované niobem na hrubé profilové trati v Liberty Ostrava a.s. V první části práce byl ověřován vliv snížené válcovací teploty před 6. stolicí v případě plochých tyčí a před 7. stolicí v případě kruhové tyče. Téměř u všech experimentů bylo dosaženo lepších hodnot tažnosti a nárazové práce. V druhé části byla na základě dosažených výsledků vybrána kruhová tyč O100, která byla podrobněji analyzována laboratorními metodami. Byla stanovena teplota rozpouštění karbonitridů při ohřevu, která následně sloužila jako teplota ohřevu pro následné PSCT simulace reálného válcování 7 úběry při různých válcovacích teplotách, ze kterých byly provedeny mikrostrukturní analýzy včetně transmisní elektronové mikroskopie (TEM). Pro danou tyč byl následně sestaven mikrostrukturní model, který po porovnání s mikrostrukturou vykazoval velmi dobrou přesnost.Master thesis deals with the analysis of the developement of the microstructure of S355J2 niobium microalloyed steel on the heavy rolling mill in Liberty Ostrava a.s. In the first part, the effect of reduced rolling temperature was verified before the 6th stand in the case of flat bars and before the 7th stand in the case of a round bar. Better values of impact toughness and ductility were obtained in almost all experiments. In the second part, based of the achieved results, a round bar O100 was selected to be analyzed in more detail by laboratory simulations. Carbonitrides dissolution temperature during heating was determined, which subsequently served as the heating temperature for further PSCT simulations of a real forming proces which consisted of 7 passes at different rolling temperatures, from which microstructural analysis were performed, including transmission electron microscopy (TEM). A microstructural model was then built for the given round bar, which showed very good accuracy after comparison with the microstructure results.633 - Katedra tváření materiáluvýborn

Study of hot deformation behavior of CuFe2 alloy

Nil strength temperature of 1062 degrees C and nil ductility temperature of 1040 degrees C were experimentally set for CuFe2 alloy. The highest formability at approx. 1020 degrees C is unusable due to massive grain coarsening. The local minimum of ductility around the temperature 910 degrees C is probably due to minor formation of gamma-iron. In the forming temperatures interval 650-950 degrees C and strain rate 0.1-10 s(-1) the flow stress curves were obtained and after their analysis hot deformation activation energy of 380 kJ.mol(-1) was achieved. Peak stress and corresponding peak strain values were mathematically described with good accuracy by equations depending on Zener-Hollomon parameter.Web of Science64270670

Hot deformation behavior of non-alloyed carbon steels

The hot deformation behavior of selected non-alloyed carbon steels was investigated by isothermal continuous uniaxial compression tests. Based on the analysis of experimentally determined flow stress curves, material constants suitable for predicting peak flow stress sigma(p), peak strain epsilon(p) and critical strain epsilon(crDRX) necessary to induce dynamic recrystallization and the corresponding critical flow stresses sigma(crDRX) were determined. The validity of the predicted critical strains epsilon(crDRX) was then experimentally verified. Fine dynamically recrystallized grains, which formed at the boundaries of the original austenitic grains, were detected in the microstructure of additionally deformed specimens from low-carbon investigated steels. Furthermore, equations describing with perfect accuracy a simple linear dependence of the critical strain epsilon(crDRX) on peak strain epsilon(p) were derived for all investigated steels. The determined hot deformation activation energy Q decreased with increasing carbon content (also with increasing carbon equivalent value) in all investigated steels. A logarithmic equation described this dependency with reasonable accuracy. Individual flow stress curves of the investigated steels were mathematically described using the Cingara and McQueen model, while the predicted flow stresses showed excellent accuracy, especially in the strains ranging from 0 to epsilon(p).Web of Science152art. no. 59

Analysis of the microstructure development of Nb-microalloyed steel during rolling on a heavy-section mill

It is not realistic to optimize the roll pass design of profile rolling mills, which typically roll hundreds of profiles, using physical modelling or operational rolling. The use of reliable models of microstructure evolution is preferable here. Based on the mathematical equations describing the microstructure evolution during hot rolling, a modified microstructure evolution model was presented that better accounts for the influence of strain-induced precipitation (SIP) on the kinetics of static recrystallization. The time required for half of the structure to soften, t(0.5), by static recrystallization was calculated separately for both situations in which strain-induced precipitation occurred or did not occur. On this basis, the resulting model was more sensitive to the description of grain coarsening in the high-rolling-temperature region, which is a consequence of the rapid progress of static recrystallization and the larger interpass times during rolling on cross-country and continuous mills. The modified model was verified using a plain strain compression test (PSCT) simulation of rolling a 100-mm-diameter round bar performed on the Hydrawedge II hot deformation simulator (HDS-20). Four variants of simulations were performed, differing in the rolling temperature in the last four passes. For comparison with the outputs of the modified model, an analysis of the austenite grain size after rolling was performed using optical metallography. For indirect comparison with the model outputs, the SIP initiation time was determined based on the NbX precipitate size distribution obtained by TEM. Using the PSCT and the outputs from the modified microstructure evolution model, it was found that during conventional rolling, strain-induced precipitation occurs after the last pass and thus does not affect the austenite grain size. By lowering the rolling temperature, it was possible to reduce the grain size by up to 56 mu m, while increasing the mean flow stress by a maximum of 74%. The resulting grain size for all four modes was consistent with the operating results.Web of Science161art. no. 28

Hot deformation behaviour of Mn-Cr-Mo low-alloy steel in various phase regions

The deformation behaviour of a coarse-grained as-cast medium-carbon steel, alloyed with 1.2% Mn, 0.8% Cr and 0.2% Mo, was studied by uniaxial compression tests for the strain rates of 0.02 s(-1)-20 s(-1)in the unusually wide range of temperatures (650-1280 degrees C), i.e., in various phase regions including the region with predominant bainite content (up to the temperature of 757 degrees C). At temperatures above 820 degrees C, the structure was fully austenitic. The hot deformation activation energies of 648 kJ center dot mol(-1)and 364 kJ center dot mol(-1)have been calculated for the temperatures = 770 degrees C, respectively. This corresponds to the significant increase of flow stress in the low-temperature bainitic region. Unique information on the hot deformation behaviour of bainite was obtained. The shape of the stress-strain curves was influenced by the dynamic recrystallization of ferrite or austenite. Dynamically recrystallized austenitic grains were strongly coarsened with decreasing strain rate and growing temperature. For the austenitic region, the relationship between the peak strain and the Zener-Hollomon parameter has been derived, and the phenomenological constitutive model describing the flow stress depending on temperature, true strain rate and true strain was developed. The model can be used to predict the forming forces in the seamless tubes production of the given steel.Web of Science109art. no. 125

Deficient methylation and formylation of mt-tRNA(Met) wobble cytosine in a patient carrying mutations in NSUN3.

Epitranscriptome modifications are required for structure and function of RNA and defects in these pathways have been associated with human disease. Here we identify the RNA target for the previously uncharacterized 5-methylcytosine (m(5)C) methyltransferase NSun3 and link m(5)C RNA modifications with energy metabolism. Using whole-exome sequencing, we identified loss-of-function mutations in NSUN3 in a patient presenting with combined mitochondrial respiratory chain complex deficiency. Patient-derived fibroblasts exhibit severe defects in mitochondrial translation that can be rescued by exogenous expression of NSun3. We show that NSun3 is required for deposition of m(5)C at the anticodon loop in the mitochondrially encoded transfer RNA methionine (mt-tRNA(Met)). Further, we demonstrate that m(5)C deficiency in mt-tRNA(Met) results in the lack of 5-formylcytosine (f(5)C) at the same tRNA position. Our findings demonstrate that NSUN3 is necessary for efficient mitochondrial translation and reveal that f(5)C in human mitochondrial RNA is generated by oxidative processing of m(5)C.This work was funded by the Medical Research Council (MRC; as part of the core funding for the Mitochondrial Biology Unit MC_U105697135 and by the G0801904 grant), the European Research Council (ERC; 310360), Cancer Research UK (CR-UK; C10701/ A15181), European Commission (FP7/2007-2013, under grant agreement number no.262055 (ESGI), as a Transnational Access project of the European Sequencing and Genotyping Infrastructure), core support grant from the Wellcome Trust and MRC to the Wellcome Trust-MRC Cambridge Stem Cell Institute, the European Commission (Horizon2020, under grant agreement number 633974), the Bundesministerium fur Bildung und Forschung (BMBF) (through the German Network for mitochondrial disorders (mitoNET, 01GM1113C) and through the European network for mitochondrial disorders (E-Rare project GENOMIT, 01GM1207)) and by EMBO (ALFT 701-2013).This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/ncomms1203

Integrating Signals from the T-Cell Receptor and the Interleukin-2 Receptor

T cells orchestrate the adaptive immune response, making them targets for immunotherapy. Although immunosuppressive therapies prevent disease progression, they also leave patients susceptible to opportunistic infections. To identify novel drug targets, we established a logical model describing T-cell receptor (TCR) signaling. However, to have a model that is able to predict new therapeutic approaches, the current drug targets must be included. Therefore, as a next step we generated the interleukin-2 receptor (IL-2R) signaling network and developed a tool to merge logical models. For IL-2R signaling, we show that STAT activation is independent of both Src- and PI3-kinases, while ERK activation depends upon both kinases and additionally requires novel PKCs. In addition, our merged model correctly predicted TCR-induced STAT activation. The combined network also allows information transfer from one receptor to add detail to another, thereby predicting that LAT mediates JNK activation in IL-2R signaling. In summary, the merged model not only enables us to unravel potential cross-talk, but it also suggests new experimental designs and provides a critical step towards designing strategies to reprogram T cells

Femtosecond Dynamics of the Ring Closing Process of Diarylethene: A Case Study of Electrocyclic Reactions in Photochromic Single Crystals

The cyclization reaction of the photochromic diarylethene derivative 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene was studied in its single crystal phase with femtosecond transient absorption spectroscopy. The transient absorption measurements were performed with a robust acquisition scheme that explicitly exploits the photoreversibility of the molecular system and monitors the reversibility conditions. The crystalline system demonstrated 3 × 104 repeatable cycles before significant degradation was observed. Immediately following photoexcitation, the excited state absorption associated with the open-ring conformation undergoes a large spectral shift with a time constant of approximately 200 fs. Following this evolution on the excited state potential energy surface, the ring closure occurs with a time constant of 5.3 ps, which is significantly slower than previously reported measurements for similar derivatives in the solution phase. Time resolved electron diffraction studies were used to further demonstrate the assignment of the transient absorption dynamics to the ring closing reaction. The mechanistic details of the ring closing are discussed in the context of prior computational work along with a vibrational mode analysis using density functional theory to give some insight into the primary motions involved in the ring closing reaction

Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTIC‐HF: baseline characteristics and comparison with contemporary clinical trials

Aims: The safety and efficacy of the novel selective cardiac myosin activator, omecamtiv mecarbil, in patients with heart failure with reduced ejection fraction (HFrEF) is tested in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTIC‐HF) trial. Here we describe the baseline characteristics of participants in GALACTIC‐HF and how these compare with other contemporary trials. Methods and Results: Adults with established HFrEF, New York Heart Association functional class (NYHA) ≥ II, EF ≤35%, elevated natriuretic peptides and either current hospitalization for HF or history of hospitalization/ emergency department visit for HF within a year were randomized to either placebo or omecamtiv mecarbil (pharmacokinetic‐guided dosing: 25, 37.5 or 50 mg bid). 8256 patients [male (79%), non‐white (22%), mean age 65 years] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NT‐proBNP 1971 pg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTIC‐HF randomized patients representative of recent HF registries and trials with substantial numbers of patients also having characteristics understudied in previous trials including more from North America (n = 1386), enrolled as inpatients (n = 2084), systolic blood pressure < 100 mmHg (n = 1127), estimated glomerular filtration rate < 30 mL/min/1.73 m2 (n = 528), and treated with sacubitril‐valsartan at baseline (n = 1594). Conclusions: GALACTIC‐HF enrolled a well‐treated, high‐risk population from both inpatient and outpatient settings, which will provide a definitive evaluation of the efficacy and safety of this novel therapy, as well as informing its potential future implementation

Hot flow stress model of CuFe2 alloy

Bakalářská práce se zabývá možností popisu přirozeného deformačního odporu slitiny CuFe2 modelem Hensel-Spittel. Experimentální data byla získána ze série zkoušek jednoosým tlakem, které probíhaly při teplotách deformace 650, 750, 850 a 950 °C a nominálních deformačních rychlostech 0,1, 1 a 10 s-1. Získané křivky deformace-napětí byly vyhlazeny softwarem Origin. Z hodnot píkových napětí byla pomocí softwaru ENERGY 4.0 stanovena hodnota aktivační energie. Ze zbylých konstant vyčíslených softwarem ENERGY 4.0 bylo matematicky popsáno píkové napětí a deformace do píku jako funkce Zener-Hollomonova parametru. Hodnoty materiálových konstant modelu Hensel-Spittel byly vyčísleny vícenásobnou nelineární regresí softwarem UNISTAT. Predikované hodnoty deformačních odporů vykazovaly u nízkých teplot deformace poměrně dobrou přesnost. Naopak se zvyšující se teplotou narážel model Hensel-Spittel na svou fenomenologickou podstatu a křivky deformace-napětí nebyl schopen přesněji popsat.Bachelor thesis deals with the possibility of the description of hot flow stress with the Hensel-Spittel model. Experimental data were obtained from a series of uniaxial compression tests performed at deformation temperature of 650, 750, 850 a 950 °C and strain rates of 0,1, 1 a 10 s-1. The stress-strain curves were smoothed out in software Origin. Peak stress values were used to determine the value of activation energy in software ENERGY 4.0. From the remaining constants calculated by ENERGY 4.0 software, the peak stress and peak strain as a function of Zener-Hollomon parameter were mathematically described. The material constants of the Hensel-Spittel model were determined by multiple non-linear regression in software UNISTAT. Predicted values of hot flow stress showed relatively good accuracy at low temperatures. On the contrary, as the temperature increased, the Hensel-Spittel model hit its phenomenological phenomenon and was unable to predict the stress-strain curve more accurately.633 - Katedra tváření materiáluvýborn