Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are ...different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR) of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM) and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel.
Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are ...different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR) of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM) and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel.
One of the most influential microstructure constituents in creep resistant steels are carbide particles. Carbide particles act as obstacles to dislocations movement, therefore the creep rate strongly ...depends on their size and distribution. At elevated temperatures to which creep resistant steels are exposed, carbide morphology is altered by the coarsening mechanism, consequently deteriorating the creep resistance of these steels. The aim of this work is to study the role of size and distribution of carbide particles on creep rate. Different distributions and size of carbides were obtained by different heat treatment conditions. The effect of different carbide morphology on the creep resistance was evaluated by uniaxial constant load creep tests.
Specimens of high chromium creep resistant steel were tempered at 800 °C for different times and examined in SEM. After short tempering stringers of cementite particles are formed at ferrite grain ...boundaries. By longer tempering, the content of chromium and molybdenum increase up to Cr18Fe3Mo2C6 and the number of stringers decreases what gradually increase the creep rate.
U ovom istraživanju razvijeni su dva nova testa, tj. test sa kontinuiranom unutarnjim vodenim hlađenjem, kao i test sa diskontinuiranom unutarnjim vodenim i zračnim hlađenjem. Dokazano je da je prvi ...tip ispitivanja primjeran za simulaciju vremenske raspodjele temperature na odabranoj dubini termalno opterećene površine alata za vruću preradu. Druga vrsta ispitivanja je prikladno za proučavanje otpora termalnog zamora alatnog materijala.
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•Nanopatterning surfaces using grazing incidence swift heavy ions has been demonstrated.•Various morphologies of surface modifications can be chosen by irradiation ...parameters.•Irradiated surafces can be further post-processed by etching and annealing.
Nanopatterned surfaces play a key role for many applications exploiting unique features such as an enhanced surface area, long- and short-ranged morphology modulations or a spatial variation of electronic and chemical properties. Ion beam irradiation has been frequently used for nanostructuring bulk materials because it is efficient, fast, and cost-effective. In this paper we show that ion irradiation under extremely grazing incidence in conjunction with other scalable processing methods such as wet etching and thermal annealing, is a perfect tool for nanopatterning of dielectric surfaces. We demonstrate that by tuning ion energy and fluence, one can select different surface nanopattern morphologies like individual chains of nanohillocks, nanostripes, or nanoscaled ripples. Furthermore, chemical etching of the irradiated surface can be used to create a negative replica of the nanopattern as only the material making up the surface track is susceptible to the etching process and is thus removed. Also, a removal of the surface track can be achieved by thermal annealing in vacuum. All these presented strategies open up new ways for achieving control over nanoscale surface modifications using swift heavy ion beams.
The aim was to establish a registry of patients with a diagnosis of Takotsubo cardiomyopathy (TC) to help learn more about the characteristics, treatment strategies, and natural history of this ...disease. Data for patients with TC diagnosed from July 2004 to April 2008 at 2 major hospitals in Rhode Island were obtained. A data set was created that included baseline demographics and characteristics, hospital, course, and clinical outcomes. TC was diagnosed in 70 patients during the study period. Postmenopausal women comprised 95% of the cohort. Six patients presented with cardiogenic shock, 9 required intubation, 3 experienced sustained ventricular arrhythmias, and 1 patient died of cardiac causes. Average ejection fraction was 37% at cardiac catheterization. Troponin-I was increased in all except 1 patient. Follow-up echocardiography showed full recovery of wall motion abnormalities, with an average ejection fraction of 59%. Most patients were treated using standard cardiovascular medications for acute coronary syndrome, and 43% were discharged on warfarin therapy because of severe apical wall motion abnormalities. Univariate analysis suggested that long-term use of angiotensin-converting enzyme inhibitors before the onset of TC was protective against cardiogenic shock, sustained ventricular arrhythmia, and death. Consecutive cases grouped into different seasons showed a statistically significant spike in the occurrence of TC during the summer months. In conclusion, the acute phase of this condition may lead to critical illness and death, and use of an angiotensin-converting enzyme inhibitor may have a protective effect. Overall long-term prognosis and recovery of left ventricular function were excellent.
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