Papers by Keyword: CCT

Abstract: The effect of chromium content and prior hot deformation of the austenite on the continuous cooling transformation (CCT) diagram of a newly developed low-carbon bainitic steel has been studied using dilatometer measurements conducted on a Gleeble 3800 simulator with cooling rates ranging from 2-80 °C/s. After austenitization at 1100 °C, specimens were either cooled without strain or given 0.6 strain at 880 °C prior to dilatometer measurements. The resultant microstructures have been studied using laser scanning confocal microscopy, scanning electron microscopy and macrohardness measurements. CCT and deformation continuous cooling transformation (DCCT) diagrams were constructed based on the dilatation curves, final microstructures and hardness values. Depending on the cooling rate, the microstructures of the investigated steels after cooling from the austenite region consist of one or more of the following microstructural components: lath-like upper bainite, i.e. bainitic ferrite (BF), granular bainite (GB), polygonal ferrite (PF) and pearlite (P). The proportion of BF to GB as well as the hardness of the transformation products decreased with decreasing cooling rate. The cooling rate at which PF starts to appear depends on the steel composition. With both undeformed and deformed austenite, increasing the chromium content led to higher hardenability and refinement of the microstructure, promoting the formation of BF and shifting the ferrite start curve to lower cooling rates. Prior hot deformation shifted the transformation curves to shorter times and higher temperatures and led to a reduction in hardness at the low cooling rates through the promotion of ferrite formation.

Abstract: White light-emitting diode (LED) is used in a new generation of solid-state lighting due to its advantages in energy saving and environmental friendliness. Based on this assumption, Emphasis was put on trying to establish a laboratory technique to convert UV-blue light into white light by using polymeric materials. In this work, an laboratory technique to convert UV-blue light into white light by using polymeric materials, consisting of red (R), green (G) and blue (B) for a white light generation. The project employed the use Colouring polymorph plastic as an active materials mixed with Silicone Sealant in different ratio and pumping by UV-Blue light. Colour rendering index (CRI) and correlated colour temperature (CCT) as main measurement parameters to evaluate the performance of the white light. The best white light appearance an indicated by photo and colour meter were achieved by mixing red (R), 0.05gm and green (G), 0.1gm the optimum results were CCT =3606k, CRI =70.3, x=0.3661, y=0.2925, and by mixing red (R), 0.005gm and green (G), 0.005gm the results were CCT=4891 k, CRI =63.8 and x=0.3359, y=0.2405.

Abstract: In this study, the chromaticity properties of curcuminoids nanofibers were studied. Recent studies revealed that the nature of emitted light from curcuminoids and the poor stability which limits their illumination applications can be further improved using nanofibers and nanoparticles of curcuminoids. Motivated by this idea, we prepared some Poly(methyl methacrylate) (PMMA) integrated curcuminoids nanofibers via electrospinning. Poly(methyl methacrylate) (PMMA) were used in three types of concentration (5,10 and15wt%) which were mixed with (curcuma longa L.) powder to produce curcuminoids solution by using the centrifuge to separate the curcuminoids solution from the impurities. Different amounts of polymer solution mixed with curcuminoids (1 to 5ml) were spun by electrospinning to study its properties. The effect of annealing on samples was studied. The chromatic study of the samples and the effect of the amount and concentration of the solution were studied by pumping the samples in three different light emitting diode (LED) wavelengths (365, 390 and 445nm). The white light chromaticity coordinates (CIE), correlated color temperature (CCT) and color rendering index (CRI) were measured. The optimum CIE, CRI and CCT values of (X= 0.3051; Y= 0.3370), 64 and 6809K, respectively were obtained. By using field emission scanning electron microscope (FESEM) device, the curcuminoids nanofibers diameter was measured, where the values obtained ranged between 191 to 234nm. After the annealing process, curcuminoids nanoparticles average diameter 13-19 nm were obtained.

Abstract: The polycrystalline ceramic named calcium and copper titanate is a dielectric ceramic with very high dielectric constant applicable in several electronic devices. The powder form for that advanced ceramic can be synthesized through chemical route, like the Polymeric Precursor Method at relative lower temperatures the presence of alkaline earth cations harms the structural homogenization during the crystallization process. In this work, the calcium and copper titanate powder was obtained by Polymeric Precursors Method by imposing a slow thermal decomposition of polymeric precursor and several crushing steps before the calcination at 800 °C for 4 hours. The entire process was observed by thermogravimetric analysis and FTIR spectrometry, including the nitrogen adsorption-desorption isotherms and X-ray diffractometry techniques for calcined power samples. It was observed the crystallization of the cubic Im-3 Ca_1/4Cu_3/4TiO₃ phase only starts after organics removal and full calcium carbonate elimination above 700 oC, which is followed by pore elimination and particle sintering. The chemical synthetic route used in this work shows the ability to prepare CCT powders sample with very structural homogeneity, which characteristics are required to manufacturing many electronic devices.

Abstract: The microstructural evolution of the high Nb X80 pipeline steel in Continuous Cooling Transformation (CCT) by Gleeble-3500HS thermal mechanical simulation testing system was studied, the corresponding CCT curves were drawn and the influence of some parameters such as deformation and cooling rate on microstructure of high Nb X80 pipeline steel was analyzed. The results show that as cooling rate increased, the phase transformation temperature of high Nb X80 steel decreased, with the microstructure transformation from ferrite-pearlite to acicular ferrite and bainite-ferrite. When cooling rate was between 20°C/s and 30°C/s, the microstructure was comparatively ideal acicular ferrite, thermal deformation accelerates phase transformation notably and made the dynamic CCT curves move upward and the initial temperature of phase transformation increase obviously. Meanwhile the thermal deformation refined acicular ferrite and extended the range of cooling rate accessible to acicular ferrite.

Abstract: The purpose of this investigation is focused on two high strength low alloy steels for offshore application. TTT, CCT curves, Vickers depth profiles and microstructures of direct water quenched steels are evaluated in the experiment. Microhardness of the direct quenched surface is as high as 400 Hv, and the central region hardness of water quenched specimen is above 250 Hv. Martensite dominates the microstructure of quenched surface. In contrast, the mixture of martensite, bainite and ferrite is widely observed from the center of quenched specimen.

Abstract: Continuous cooling dynamic transformation regularity of T700 was investigated by gleeble-3500. The results show when the cooling rate is small organization is mainly composed of polygonal ferrite and pearlite and has minor banded organization. With the increase of cooling rate, begin to appear granular bainite. When cooling rate reaches 3/s or more, ferrite changes to quasi polygon, and start to appear small amount of bainite. when the cooling rate is 7°C/s, pearlite is disappeared in structure, granular bainite increases, quasipolygonal ferrite content is gradually decreased. When the cooling rate is increased to 10°C/s or above, organization is granular bainite.

Abstract: Continuous cooling static transformation regularity of T700 was investigated by gleeble-3500, the results show when the cooling rate is small organization is mainly composed of ferrite and pearlite. With the increase of cooling rate, begin to appear granular bainite. When the cooling rate is 10-20 °C /s, microstructure is acicular ferrite and bainite. Along with the cooling speed further increasing, martensite begins to appear in organize, and with the increase of cooling rate, martensite content gradually increase.

Abstract: Digitization of CCT curves by systemically using common softwares was studied and practiced to rebuild the digital patterns for teaching purpose. As treated in PC procedure, the CCT images printed in books were transformed into the digital data points, which can be read and record clearly and precisely in computer, extremely changing the appearance and precision of raw images. As the digital data, this digitized CCT curves can be conveniently introduced into the courseware, drawing more attendance and interesting from students than raw images. On the other hand, these digitized data also can be used as the CCT database for industrial applications, which can introduce automation into the thermal treatment industry. That is, the digitization of CCT curves will take great advantage of the improvement of teaching and promote the producing depth.

Abstract: Age hardening is one of the most important processes to strengthen aluminium alloys. It usually consists of the steps solution annealing, quenching and aging. For heat treatment simulations as well as for the appropriate choice of quenching processes in heat treatment shops, knowledge of the temperature- and time-dependent precipitation behaviour during continuous cooling is required. Quenching should happen as fast as necessary to reach high strengths, but also as slow as possible, to reduce residual stresses and distortion. This optimal quenching rate of an aluminium component depends on its chemical composition, initial microstructure and solution annealing parameters as well as on its dimensions. Unfortunately continuous cooling transformation (CCT) diagrams of aluminium alloys do almost not exist. Instead isothermal transformation (IT) diagrams or given average quenching rates are used to estimate quenching processes, but they are not satisfying neither for heat treatment simulations nor for heat treatment shops. Thermal analysis, especially Differential Scanning Calorimetry (DSC) provides an approach for CCT-diagrams of aluminium alloys, if the relevant quenching rates can be realized in the DSCequipment. The aluminium alloy Al-4.5Zn-1Mg (7020) is known for its relatively low quenching sensitivity as well as for its technical importance. The complete CCT-diagram of 7020 with cooling rates from a few K/min to some 100 K/min has been recorded. Samples have been solution annealed and quenched with different cooling rates in a high speed DSC. The resulting precipitation heat peaks during cooling have been evaluated for temperature and time of precipitation start, as well as their areas as a measure for the precipitate amount. Quenched samples have been further investigated regarding their microstructure by light and electron microscopy, hardness after aging and precipitation behaviour during re-heating in DSC. The CCT-diagram correlated very well with the microstructure, hardness and re-heating results. A critical cooling rate with no detectable precipitation during continuous cooling 155 K/min could be determined for 7020. A model to integrate the CCT-diagram in heat treatment simulation of aluminium alloys is under development.