High-strength steels are used more than general structural steel due to their combination of properties such as high strength, good toughness and weldability. They are mainly used in the manufacture of heavy vehicles for the mining industry, cranes, transportation, etc. However, welding these grades of steel brings new challenges. Also, a simulation for welding high-strength steel is required more often. To insert a material database into the simulation program, it is necessary to conduct investigations using CCT (Continuous Cooling Transformation) diagrams, welded joints research, and more. To investigate the behavior of S960MC steel during heating and cooling, we used dilatometry analysis supported by EBSD (Electron Backscatter Diffraction) analysis. A CCT diagram was constructed. The transformation temperatures of Ac1 and Ac3 increase with increasing heating rate. The Ac1 temperature increased by 54 °C and the Ac3 temperatures by 24 °C as the heating rate increased from 0.1 °C/s to 250 °C/s. The austenite decomposition temperatures have a decreasing trend in the cooling phase with increasing cooling rate. As the cooling rate changes from 0.03 °C/s to 100 °C/s, the initial transformation temperature drops from 813 °C to 465 °C. An increase in the cooling rate means a higher proportion of bainite and martensite. At the same time, the hardness increases from 119 HV10 to 362 HV10.
- Klíčová slova
- CCT diagram, dilatometry analysis, high-strength steels,
- Publikační typ
- časopisecké články MeSH
The combined effect of deformation temperature and strain value on the continuous cooling transformation (CCT) diagram of low-alloy steel with 0.23% C, 1.17% Mn, 0.79% Ni, 0.44% Cr, and 0.22% Mo was studied. The deformation temperature (identical to the austenitization temperature) was in the range suitable for the wire rolling mill. The applied compressive deformation corresponded to the true strain values in an unusually wide range. Based on the dilatometric tests and metallographic analyses, a total of five different CCT diagrams were constructed. Pre-deformation corresponding to the true strain of 0.35 or even 1.0 had no clear effect on the austenite decomposition kinetics at the austenitization temperature of 880 °C. During the long-lasting cooling, recrystallization and probably coarsening of the new austenitic grains occurred, which almost eliminated the influence of pre-deformation on the temperatures of the diffusion-controlled phase transformations. Decreasing the deformation temperature to 830 °C led to the significant acceleration of the austenite → ferrite and austenite → pearlite transformations due to the applied strain of 1.0 only in the region of the cooling rate between 3 and 35 °C·s-1. The kinetics of the bainitic or martensitic transformation remained practically unaffected by the pre-deformation. The acceleration of the diffusion-controlled phase transformations resulted from the formation of an austenitic microstructure with a mean grain size of about 4 µm. As the analysis of the stress-strain curves showed, the grain refinement was carried out by dynamic and metadynamic recrystallization. At low cooling rates, the effect of plastic deformation on the kinetics of phase transformations was indistinct.
- Klíčová slova
- CCT diagram, austenitization temperature, dynamic recrystallization, low-alloy steel, phase transformations, plastic deformation,
- Publikační typ
- časopisecké články MeSH
Continuous cooling transformation (CCT) diagrams are widely used when heat treating steels and represent which type of phase will occur in a material as it is cooled at different cooling rates. CCT diagrams are constructed on the basis of dilatometry measurements on relatively small testing samples (cylindrical shape with diameter of 4mm and length of 11 mm in this study). The main aim of this work was to demonstrate the possibility of evaluating the tensile test properties using mini-tensile tests from miniature volumes (1.4 × 10-7 m3 for one sample) subsequent to determination of the CCT diagram and to extend a standard CCT diagram with information about strength, ductility and the estimated value of the work-hardening coefficient. Mini-tensile tests (MTT) were recently developed due to the low availability of experimental material and have already been successfully used for local mechanical property characterization of metals. CCT diagrams were constructed for 42CrMo4 steel prepared by the laser-directed energy deposition (L-DED) process, for commercially available 42CrMo4 steel conventionally manufactured (for comparison of traditional processing and AM preparation) and for H13 tool steel deposited by the selective laser melting (SLM) process.
- Klíčová slova
- continuous cooling transformation diagram, laser directed energy deposition, mini-tensile test, selective laser melting,
- Publikační typ
- časopisecké články MeSH
Phosphors have been used as wavelength converters in illumination for many years. When it is excited with blue light, the frequently used yttrium aluminium garnet doped with cerium (YAG:Ce) phosphor converts a part of blue light to a wideband yellow light, resulting in the generated light having a white color. By combining an appropriate concentration of the YAG:Ce phosphor and blue excitant light, white light of a desired correlated color temperature (CCT) can be obtained. However, this type of illumination has a lower color rendering index value (CRI). In an attempt to improve the CRI value, we mixed the YAG:Ce phosphor with europium-doped calcium sulfide phosphor (CaS:Eu), which resulted in a considerably increased CRI value. This article examines an experiment with luminescent layers consisting of a mixture of selected phosphors and polydimethylsiloxane (PDMS). Different thicknesses in these layers were achieved by changing the speed of rotation during their accumulation onto laboratory glass using the method of spin coating. The spectral characteristics of these luminescent layers as they were excited with blue light emitting diode (LED) and laser diode (LD) were then determined. A suitable combination of the YAG:Ce phosphor with a phosphor containing europium, as it was excited with a blue LED, yielded a source of white light with a CRI value of greater than 85. The response time in the tested luminescent layers to a rectangular excitant impulse (generated by a signal generator and transmitted by LD) was also measured in order to examine their potential use in visible light communications (VLC).
- Klíčová slova
- color rendering index value, correlated color temperature, visible light communication,
- Publikační typ
- časopisecké články MeSH
The paper is focused on investigation of the high-strength AISI 4340 steel at various temperature and deformation conditions. The article is divided into two specific analyses. The first is to examine the dilatation behavior of the steel at eight different cooling rates, namely, 100, 10, 5, 1, 0.5, 0.1, 0.05 and 0.01 °C·s-1. The mapping of the phase transformations due to varying cooling rates from the austenitizing temperature of 850 °C allows the construction of the CCT diagram for a given high-strength steel. These dilatation curves were also compared with the metallography of the selected samples for the proper construction of the CCT diagram. A further analysis of the high temperature deformation of high strength steel AISI 4340 was performed in the range of temperature 900-1200 °C, and the strain rate was in the range from 0.001 to 10 s-1 with maximum value of the true strain 0.9. Changes in the microstructure were observed using light optical microscopy (LOM). The effect of hot deformation temperature on true stress, peak stress and true strain was investigated. The hardness of all deformed samples, depending on the temperature, the deformation rate and the peak stress σp overall together related with hardness, has also been evaluated.
- Klíčová slova
- CCT diagram, dilatometry, true strain, true stress,
- Publikační typ
- časopisecké články MeSH
UNLABELLED: The objective of the study was to determine whether there exists a difference in the central cornea thickness (CCT) in patients with hypertensive (HTG) and normotensive glaucoma (NTG), and subsequently, to compare the application of prostaglandins by corrected CCT (CCT correction) for both types of glaucoma. MATERIAL AND METHODS: 100 eyes of 50 patients (the average age of 67) with HTG and 100 eyes of 50 patients (the average age of 62.6) with NTG were examined. Antiglaucomatics, if indicated, were taken by the patients for at least the preceding five years. The excluding criteria in the study were: cornea diseases, post-laser procedure conditions and high ametropia. CCT was measured by means of Tomey Handy Pachymeter SP100 by the same physician. RESULTS: A two-sample t-test was applied in order to compare the measurement values of CCT and the subsequent correction of these values (CCT correction) in patients with HTG and NTG. The statistical evaluation showed that in case of both CCT and CCT correction, the values were lower in the group of NTG patients in comparison with HTG patients. With respect to CCT, the difference was statistically insignificant (NTG 554.9±35.7 vs. HTG 561.4 ± 32.7, p = 0.181). In case of CCT correction, the difference was more considerable, but still statistically insignificant (NTG 550.8 ± 35 vs. HTG 559.6 ± 33.1, p = 0.06). CONCLUSION: CCT was higher in NTG than in HTG; however, these values were statistically insignificant. A comparison of the application of prostaglandins of corrected CCT (CCT correction) for both types of glaucoma increased the difference, but this difference was still statistically insignificant. This difference was caused by an uneven representation of patients treated with prostaglandins in both groups. Key words: hypertensive glaucoma, normotensive glaucoma, central cornea thickness, prostaglandins.
- Klíčová slova
- central cornea thickness, hypertensive glaucoma, normotensive glaucoma, prostaglandins,
- MeSH
- glaukom * komplikace MeSH
- lidé středního věku MeSH
- lidé MeSH
- nitrooční tlak * MeSH
- prostaglandiny syntetické MeSH
- rohovka * patologie MeSH
- senioři MeSH
- Check Tag
- lidé středního věku MeSH
- lidé MeSH
- senioři MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- prostaglandiny syntetické MeSH
UNLABELLED: Central corneal thickness (CCT) was measured in 328 eyes of 167 patients (50 men and 117 women, an average age was 62 years). CCT was determinated by ultrasonic pachymeter NIDEC, design UP-1000, at Eye Department of 3rd Medical Faculty of Prague. RESULTS: The mean CCT at glaucoma patients was 561 microns, in margins 490-650 microns. CCT for right eyes were 0.567 +/- 0.035 mm, for left eyes 0.569 +/- 0.037 mm. There were no influence by previous operations (cataract, trabeculectomy and combined operations). NTG had the lowest CCT values 551 microns, POAG had 569 microns and OHT the greates value, CCT is 588 microns. CCT in patients with NTG was significantly lower (p = 0.047) than in POAG. The higher difference is between NTG a OHT (p = 0.015). We had no statistical difference in CCT between hypermetropic, emetropic and myopic eyes. The corneal thickness is decreasing during ageing. CCT is another clinically helpful factor for evaluation our glaucoma patients. CCT together with other risk factors can help us in establishing a target pressure. Patients after refractive surgery (PRK, LASIK) should be more carefully evaluated not to miss early stages of glaucoma.
- MeSH
- glaukom patologie MeSH
- lidé středního věku MeSH
- lidé MeSH
- rohovka patologie MeSH
- rohovková topografie MeSH
- Check Tag
- lidé středního věku MeSH
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- anglický abstrakt MeSH
- časopisecké články MeSH
AIMS: To compare the changes of central corneal thickness (CCT) and intraocular pressure (IOP) post-phacoemulsification between cataract patients with and without pre-existing glaucoma. MATERIALS AND METHODS: A prospective cohort study of 86 patients with visually significant cataract: 43 with pre-existing glaucoma (GC group) and 43 without pre-existing glaucoma (CO group). CCT and IOP were evaluated at baseline (pre-phacoemulsification), as well as at 2 hours, 1 day, 1 week and 6 weeks post-phacoemulsification. RESULTS: The GC group have significantly thinner CCT pre-operatively (p = 0.003). There was a steady increase of CCT with the highest peak at 1 day post-phacoemulsification, followed by a steady decline of CCT and back to baseline at 6 weeks post-phacoemulsification in both groups. The GC group demonstrated a significant difference in CCT at 2 hours (mean difference 60.2 μm, p = 0.003) and 1 day (mean difference 70.6 μm, p = 0.002) post-phacoemulsification, compared to the CO group. There was a sudden increase in IOP at 2 hours post-phacoemulsification measured by GAT and DCT in both groups. This was followed by a gradual reduction of IOP, with significant reduction at 6 weeks post-phacoemulsification in both groups. However, there was no significant difference in IOP between the two groups. IOP measured by GAT and DCT showed strong correlation (r > 0.75, p < 0.001) in both groups. There was no significant correlation between GAT-IOP and CCT changes; nor between DCT-IOP and CCT changes in both groups. CONCLUSIONS: CCT changes post-phacoemulsification in patients with pre-existing glaucoma were similar, in spite of having thinner CCT pre-operatively. IOP measurement was not affected by CCT changes in glaucoma patients post-phacoemulsification. IOP measurement using GAT is comparable with DCT post-phacoemulsification.
- Klíčová slova
- Phacoemulsification, central corneal thickness, glaucoma, intraocular pressure,
- MeSH
- fakoemulzifikace * MeSH
- glaukom * komplikace chirurgie MeSH
- katarakta * komplikace MeSH
- lidé MeSH
- nitrooční tlak MeSH
- prospektivní studie MeSH
- rohovka MeSH
- tonometrie oční MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
UNLABELLED: The purpose of the study was to determine the dependence of intraocular pressure (IOP) measured by Goldmann applanation tonometer (AT), non-contact tonometer (BT) and Tone-Pen (TP) on central corneal thickness (CCT) as well as the respective comparison in relation to the central corneal thickness. METHODS: CCT and IOP were assessed in 106 eyes of 106 subjects aged 7-77 years (mean 34.3 +/- 17.1 years). IOP was measured with BT, TP and AT. Central corneal thickness was assessed using ultrasound pachymetry. The obtained data were statistically analyzed. RESULTS: The mean CCT in 106 eyes was 572 +/- 46 microm (range 455-701 microm). A positive correlation between IOP and CCT was found in all types of tonometry. The change in measured IOP for a 100 microm of CCT was 2.0, 2.5 and 5.6 mmHg for TP, AT and BT, respectively. CONCLUSION: IOP measurement by all three methods is affected by CCT. The BT is influenced by CCT significantly more than are AT and TP.
- MeSH
- dítě MeSH
- dospělí MeSH
- lidé středního věku MeSH
- lidé MeSH
- mladiství MeSH
- mladý dospělý MeSH
- nitrooční tlak * MeSH
- rohovka anatomie a histologie patologie MeSH
- senioři MeSH
- tonometrie oční * metody MeSH
- Check Tag
- dítě MeSH
- dospělí MeSH
- lidé středního věku MeSH
- lidé MeSH
- mladiství MeSH
- mladý dospělý MeSH
- mužské pohlaví MeSH
- senioři MeSH
- ženské pohlaví MeSH
- Publikační typ
- anglický abstrakt MeSH
- časopisecké články MeSH
UNLABELLED: The purpose of this prospective study was to determine normal central corneal thickness (CCT) and intraocular pressure (IOP) in healthy white children aged 7-17 years and to analyze their possible correlation to age and gender. Further, the possible correlations between CCT and IOP were analyzed. METHODS: CCT and IOP were assessed in 248 eyes of 124 healthy children aged 7-17 years (mean, 12.7 years). Fifty-four boys and 70 girls were included into the study. Further, the analyzed cohort was divided into subgroups of younger (7-12.4 years) and older (12.5-17 years) boys and girls. The data obtained from the whole cohort were statistically analyzed to assess normal CCT and IOP in healthy youth. Relation of CCT and IOP to age and gender, as well as relation between CCT and IOP were studied. The CCT was measured using ultrasonic pachymetry and IOP by means of Goldmann applanation tonometry. RESULTS: The mean CCT +/- SD in 124 children was 554 +/- 33 microm (range, 437-641 microm); no influence of age or gender was detected. The mean IOP +/- SD in the whole cohort was 14.5 +/- 2.6 mm Hg (range, 10-25 mm Hg). Statistically significant difference of 0.7 mm Hg was found between boys and girls, where the mean IOP was 14.1 +/- 2.3 mm Hg in boys and 14.8 +/- 2.8 mm Hg in girls respectively (p = 0.03). Age had no influence on IOP for the age range of 7-17 years (p = 0.67). The positive correlation between CCT and IOP was found. The calculated correction was 1.55 mm Hg change of IOP for 100 microm change of CCT. CONCLUSION: CCT and IOP values in healthy children aged 7-17 years are similar to values in adults. The positive correlation between both parameters seems to be of minimal clinical importance.
- MeSH
- dítě MeSH
- lidé MeSH
- mladiství MeSH
- nitrooční tlak * MeSH
- referenční hodnoty MeSH
- rohovka anatomie a histologie MeSH
- Check Tag
- dítě MeSH
- lidé MeSH
- mladiství MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- anglický abstrakt MeSH
- časopisecké články MeSH
