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Bainitic steel with 30 GPa% characteristics
The ability of a steel to be formed is often measured as the product of the ultimate tensile strength and total elongation (GPa%). The aim of the work presented in this thesis was to produce a bainitic steel by continuous cooling transformation, with a ultimate tensile strength exceeding 1000 MPa and yet having a ductility of 30%. The challenge associated with the development is that the steel must be spot-weldable, which means that the carbon concentration needs to be kept low enough to avoid the formation of martensite in the heat-affected zones of resistance spot welds.
Fundamental phase transformation theory is used for alloy design, followed by alloy manufacture and validation using a variety of microstructural and mechanical character- ization techniques. Progress is made in understanding the onset of plastic instability by critically examining the role of retained austenite in enhancing ductility. The literature on the transformation induced plasticity (TRIP) steels and factors affecting the strength and ductility in TRIPâassisted steels has been reviewed.
A model employing deformation induced martensitic transformation coupled with per- colation theory has been revisited with fresh data collated from published work to estimate the elongation of TRIP-assisted steels. A novel quantitative estimation of the stability of austenite required for optimising ductility has been developed and demonstrated to explain the new data.
Two alloys emerged from the sequence of alloy and process design, which successfully broke the 30 GPa% barrier while maintaining the ability for mass production. Furthermore, tempering of the steel at a low temperature for few hours improved ductility by softening the small amount of martensite formed during cooling to ambient temperature.
âPrematureâ failure during mechanical testing is usually due to some sort of heterogeneity in the manufactured steel. Such behaviour can sometimes be mitigated by refining the microstructure. This was investigated to see whether the required combination of strength and ductility can be achieved by reducing the scale of the parent austenite grains to achieve greater structural uniformity. However, a detailed investigation showed that lowering the austenitization temperature led to a deterioration in the properties due to microstructural banding.
Mechanical stabilization during bainitic transformation from deformed austenite in- creased the volume fraction of martensite thus making the microstructure unfavourable for optimum mechanical properties. Therefore bainite should be generated from a strainâfree recrystallised austenite grain structure.
The Habit plane, orientation relationship and associated shape strain were characterized simultaneously for the first time on individual bainite plates. The irrational habit plane of bainite measured by the two surface analysis was found to be close to {457}Îł , which is not far off the {557}Îł lath martensite habit plane reported in the literature. Pole figure analysis of three plates of bainite showed consistent results. The shear strain associated with the bainite plate is consistent with the value estimated by the phenomenological theory of martensite.Tata Steel Limite
Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTICâHF: 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 (GALACTICâHF) trial. Here we describe the baseline characteristics of participants in GALACTICâHF and how these compare with other contemporary trials.
Methods and Results:
Adults with established HFrEF, New York Heart Association functional class (NYHA)ââ„âII, EF â€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 (pharmacokineticâguided dosing: 25, 37.5 or 50âmg bid). 8256 patients [male (79%), nonâwhite (22%), mean age 65âyears] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NTâproBNP 1971âpg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTICâHF 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 pressureâ<â100âmmHg (n = 1127), estimated glomerular filtration rate <â30âmL/min/1.73 m2 (n = 528), and treated with sacubitrilâvalsartan at baseline (n = 1594).
Conclusions:
GALACTICâHF enrolled a wellâtreated, highârisk 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
Cardiac myosin activation with omecamtiv mecarbil in systolic heart failure
BACKGROUND The selective cardiac myosin activator omecamtiv mecarbil has been shown to improve cardiac function in patients with heart failure with a reduced ejection fraction. Its effect on cardiovascular outcomes is unknown. METHODS We randomly assigned 8256 patients (inpatients and outpatients) with symptomatic chronic heart failure and an ejection fraction of 35% or less to receive omecamtiv mecarbil (using pharmacokinetic-guided doses of 25 mg, 37.5 mg, or 50 mg twice daily) or placebo, in addition to standard heart-failure therapy. The primary outcome was a composite of a first heart-failure event (hospitalization or urgent visit for heart failure) or death from cardiovascular causes. RESULTS During a median of 21.8 months, a primary-outcome event occurred in 1523 of 4120 patients (37.0%) in the omecamtiv mecarbil group and in 1607 of 4112 patients (39.1%) in the placebo group (hazard ratio, 0.92; 95% confidence interval [CI], 0.86 to 0.99; P = 0.03). A total of 808 patients (19.6%) and 798 patients (19.4%), respectively, died from cardiovascular causes (hazard ratio, 1.01; 95% CI, 0.92 to 1.11). There was no significant difference between groups in the change from baseline on the Kansas City Cardiomyopathy Questionnaire total symptom score. At week 24, the change from baseline for the median N-terminal pro-B-type natriuretic peptide level was 10% lower in the omecamtiv mecarbil group than in the placebo group; the median cardiac troponin I level was 4 ng per liter higher. The frequency of cardiac ischemic and ventricular arrhythmia events was similar in the two groups. CONCLUSIONS Among patients with heart failure and a reduced ejection, those who received omecamtiv mecarbil had a lower incidence of a composite of a heart-failure event or death from cardiovascular causes than those who received placebo. (Funded by Amgen and others; GALACTIC-HF ClinicalTrials.gov number, NCT02929329; EudraCT number, 2016 -002299-28.)