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Opis: ŠTORE STEEL Ltd. is one of the three steel plants in Slovenia. Continuous cast 180 mm × 180 mm billets can undergo cooling to room temperature using a turnover cooling bed. They can also be cooled down under hoods or heat treated to reduce residual stresses. Additional operations of heat treatment from 36 h up to 72 h and cooling of the billets for 24 h, with limited capacities (with only two heat treatment furnaces and only six hoods), drastically influence productivity. Accordingly, the casting must be carefully planned (i.e., the main thing is casting in sequences), while the internal quality of the billets (i.e., the occurrence of inner defects) may be compromised. Also, the stock of billets can increase dramatically. As a result, it was necessary to consider the abandoning of cooling under hoods and heat treatment of billets. Based on the collected scrap data after ultrasonic examination of rolled bars, linear regression and genetic programming were used for prediction of the occurrence of inner defects. Based on modeling results, cooling under hoods and heat treatment of billets were abandoned at the casting of several steel grades. Accordingly, the casting sequences increased, and the stock of billets decreased drastically while the internal quality of the rolled bars remained the same.
Ključne besede: billet cooling, continuous casting, ultrasonic testing, logistic regression, genetic programming, industrial study, steel making, optimization
Objavljeno v DKUM: 25.11.2024; Ogledov: 0; Prenosov: 6
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Opis: Since additive technologies in dentistry are gradually replacing metal casting technology, it is necessary to evaluate new dental constructions intended for the development of removable partial denture frameworks. The aim of this research was to evaluate the microstructure and mechanical properties of 3D-printed, laser-melted and -sintered Co–Cr alloys, and perform a comparative study with Co–Cr castings for the same dental purposes. The experiments were divided into two groups. The first group consisted of samples produced by conventional casting of the Co–Cr alloy. The second group consisted of 3D-printed, laser-melted and -sintered specimens produced from a Co–Cr alloy powder divided into three subgroups, depending on the technological parameters chosen for manufacturing (angle, location and heat treatment). Examination of the microstructure was carried out by classical metallographic sample preparation, using optical microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX) analysis. A structural phase analysis was also performed by XRD. The mechanical properties were determined using a standard tensile test. The microstructure observation showed a dendritic character in the case of castings, while in the case of 3D-printed, laser-melted and -sintered Co–Cr alloys, the microstructure was typical for additive technologies. The XRD phase analysis confirmed the presence of Co–Cr phases (ε and γ). The results of the tensile test showed remarkably higher yield and tensile strength values and slightly lower elongation of the 3D-printed, laser-melted and -sintered samples than those produced by conventional casting.
Ključne besede: Co–Cr dental alloys, 3D printing, laser melting and sintering, casting, microstructure, mechanical properties, characterization
Objavljeno v DKUM: 21.04.2023; Ogledov: 459; Prenosov: 45
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Opis: Recent development in the computer simulation technology caused a tremendous influence on a rapid prototyping in casting process. These computational tools facilitate engineering work and urge moulding verification in foundries. Among dedicated software packages the MAGMASoft is selected for availability reasons. Its effectiveness is proved with the simulation of moulding process of the cutting teeth for a bucket wheel excavator Use of MAGMASoft enables a shortcut to a forceful and durable product, without internal cavities and micro-porosity. Such advancement of the moulding process is described in this paper.
Ključne besede: casting, porosity, wear, simulation, MAGMASoft
Objavljeno v DKUM: 03.07.2017; Ogledov: 2340; Prenosov: 143
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Opis: The results of the characterization of a CuAlNi shape-memory alloy after continuous casting technology are shown. Using this procedure a bar with a diameter of 8 mm was manufactured. After solidification of the alloy the microstructure characterization was carried out using optic microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) methods. Our results showed that the as-cast alloy consisted of the parent β1 and β1’ martensite phases. The martensite phase primary as the needle-like inside grains was observed. Martensite laths have different orientations inside particular grains. It was found that the average grains size is 98.78 µm. The grain diameter near to the external surface is higher than in the center. The average hardness of the alloy was 275 HV1.
Ključne besede: shape memory alloys, martensite, continuous casting, grain size
Objavljeno v DKUM: 16.03.2017; Ogledov: 1237; Prenosov: 124
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Opis: In this paper we present research that is connected to the performance of a series of experiments combined with the vacuum-induction melting and continuous vertical casting of a NiTi alloy in order to produce the strand. The theoretical chosen parameters made it possible to obtain a continuously cast strand with a diameter of 11 mm. The strand microstructures were investigated with a light and scanning electron microscope, while the chemical composition of the single phase was identified with the semi-quantitative micro-analysis energy-dispersive X-ray spectroscopy and inductively coupled plasma – optical emission spectrometry. The research showed that the microstructure is dendritic, where in the inter-dendritic region the eutectic is composed of a dark NiTi phase and a bright TiNi3–x phase. In some areas we found Ti carbides and phases rich in Fe. The micro-chemical analysis of the NiTi strand showed that the composition changed over the cross and longitudinal sections, which is proof that the as-cast alloys are inhomogeneous. In the final part, the electrochemical behaviours of NiTi strand samples were compared to a commercially available NiTi cast alloy with the same composition.
Ključne besede: NiTi alloy, continuous vertical casting, microstructure, potentiodynamic and impedance test
Objavljeno v DKUM: 14.03.2017; Ogledov: 1431; Prenosov: 392
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