Low alloyed steel slabs produced by continuous casting can present transverse corner cracks, which are critical due to the oxide layer formed within the crack. Understanding this type of failure and reproducibility of the phenomenon through laboratory tests is of great value for dealing with this problem. The present work analyzed samples from slab corners, where cracks were identified. The fracture surfaces were examined using a scanning electron microscope (SEM) and cut to have their microstructure analyzed with a light optical microscope (LOM). Using etching to reveal the microstructure of the samples from the slabs, it was seen that the cracks were initiated and propagated at the prior austenite grain boundaries. Furthermore, the SEM images from the corner samples were compared to those from the physical simulation of the continuous casting process from previous work, and the structure found was like the ones tested at critical temperatures. The same was noted for the microstructure analysis, where cracks were also seen to follow the grain boundaries. Therefore, it was concluded that the behavior resulted from the laboratory tests performed with in-situ melted samples with the BETA 250-5 machine were in good accordance with the reality of the continuous casting process.

The hot ductility of a low alloyed Cr-Mo steel has been investigated to evaluate the surface cracking sensitivity within the straightening or unbending regime during the continuous casting process. Tensile samples were subjected to various thermal treatments, including melting and solidification, and were tested at deforming temperatures ranging between 600 and 1100 °C using a strain rate of 10 −3 s −1 . Hot ductility was evaluated based on reduction in area measurement and metallographic investigations. The investigated steel exhibits a drop in ductility at around 800 °C due to intergranular cracking. Microstructural examinations and supplementary thermokinetic computer simulations were carried out to describe the evolution of the microstructure during solidification and cooling.

IntroductIon Because surface defects on continuously cast semi-finished steel products can cause massive defects in the final sheets, it is important to determine the causes and locations of surface flaws. Transverse crack formation in particular is influenced by many factors. The tendency for transverse cracking is related to the material properties of the strand surface and the operating mechanical and thermal stresses throughout the casting process. In reviewing the secondary cooling zone, the unbending of the strand induces critical strains on the surface, reaching ~2%. The trigger for crack formation is a surface temperature promoting high embrittlement in this cooling zone, referred to as the second ductility trough. The material behavior can deteriorate further in the presence of mold defects, such as unusually large austenite grains, oscillation marks, or uneven strand surfaces [1-5]. The temperature range of the second ductility trough is generally determined by hot tensile tests, performed in the laboratory under inert atmospheres. The samples are pulled to rupture at different testing temperatures. The ductility is directly related to the measured reduction of area (RA) of the broken samples. Authors have named different critical RA-values as indicators for surface cracking. Mintz and You [6] determined that values of 30–40% were critical. In recent decades, many studies of hot tensile testing have been done; e.g., Schwerdtfeger [7] and Mintz A new method for the experimental simulation of surface crack formation in continuous casting

奥钢联林茨公司为了生产厚355 mm、宽1 600 mm的特厚板坯,升级改造了第3炼钢厂的5号连铸机.该弧形连铸机最初设计生产的板坯最大厚度为285 mm,弧形半径为10 m,配置了直结晶器,对带液芯的铸坯进行弯曲和矫直.在这种类型的连铸机上生产厚度为355 mm铸坯的主要问题是板坯的几何形状.由于弯曲时铸坯角部变形,铸坯可能出现小的皮下热裂纹.为了模拟在浇注过程中结晶器液面到弧形段开始位置的连铸板坯变形,使用ABAQUS软件开发了有限元3D模型.该热力学模型结合材料的粘弹性定律计算浇注过程凝固坯壳的张应力和压应力.据观测,模拟计算出的浇注过程凝固坯壳的张应力和压应力的分布与小热裂纹的外形大致相符.还将抽样测量的板坯几何形状与有限元计算结果进行了比较.采用热机建模计算结果,通过优化结晶器锥度和强化出结晶器后铸坯窄面的冷却,改进了板坯的几何形状.

In the steel industry, steel slabs are produced by continuous casting to allow fast processing. A complex stress state leads to crack formation in such steel slabs. The stress components relevant for failure were identified by neutron diffraction under simulated casting conditions.

In the casting process of steels with a C‐content ranging from 0.09 to 0.53 mass%, austenite is formed as secondary crystal phase by peritectic reaction between crystal of δ ferrite and residual melt. For unalloyed or micro‐alloyed steels the C‐content or C‐equivalent influences the casting behavior of steel in the mould, such as strand shell growth, crack formation, heat transfer, temperature fluctuation in the copper plate, mould level fluctuation and oscillation marks formation. The negative casting behavior like the uneven strand shell growth, the deep oscillation mark formation, the high mould level fluctuation, the crack formation on the strand surface were found mostly for steel with C‐content or Cp between 0.10–0.13 mass%. The strand shell structure (strand shell growth, mushy zone, δ + γ phase transformation) and shrinkage of the strand shell were simulated depending on the C‐content by means of mathematical simulation. On the basis of the simulation results and of the measured high temperature strength of steel the dependence of stiffness and the irregularity of the shrinkage of strand shell on the C‐content was investigated. It was found that the stiffness and irregularity of the shrinkage of the strand shell reach the maximum value at a C‐content of about 0.12 mass%.

This paper presents the investigation work on different polymeric materials used as insulation materials of conductors in a multicore instrumentation cable. Among differently colored materials, only the white one presented cracks after a few years of use. Isothermal and non-isothermal DSC measurements were performed on initial (non-used) and aged (in service used or laboratory aged) materials as well as on raw materials in order to characterize their stability and the ageing state after storage, use in service or laboratory ageing. As shown by the oxidation induction time values, a pronounced antioxidant loss occurred for all materials during storage or service; plus a strong effect of the ambient light on stability was observed for the white insulation material. Around 3% of filler, consisting mainly of TiO2 particles (as revealed by SEM-XRF elemental analysis), was found in the white material. The higher degradability of the white material can be related to both the photocatalytic effect of the TiO2 particles and rapid loss of stabilizers. (C) 2010 Elsevier Ltd. All rights reserved.

Hot deformation of a continuously cast low alloyed steel is studied by means of hot compression and tensile tests carried out after austenitization between 700–790 °C at 3x10 -4 – 0.3 s -1 of strain rate. The ferrite transformation at the applied cooling rate was determined at 710°C by means of dilatometry. The compressive flow data obtained by using a Gleeble®1500 machine are evaluated to obtain the strain rate sensitivity and the processing maps using different models. The tensile data are used to determine the ductility of the material with different deformation parameters. A new calculation method is used for the instability parameter derived from the dynamic materials model. The strain rate sensitivity does not predict any instability but all the others instability parameters do, including the new one. Pores are formed at the prior austenitic grain boundaries at low strain rates, causing a decay of ductility in the tensile samples. A minimum in the ductility was observed for low strain rates at 750°C. Low strain rates and low temperatures increase the formation of more ferrite than without deformation at the corresponding heat treatments without deformation. In these conditions, the deformation is concentrated in the softer ferrite phase. Low power efficiency was calculated at high strain rates, where no dynamic recrystallization takes place. The domains with similar efficiency of power dissipation are correlated to deformation induced ferrite formation and ferrite recovery. These domains vary with the increasing strain.

Durch Verbesserung und Optimierung der Auslegung und Instandhaltung von Stranggießanlagen und der Gießparameter konnte die Gefahr der Bildung von Heißrissen und Heißrissseigerungen während der letzten Jahre minimiert werden. In Zusammenarbeit zwischen Voestalpine Stahl und dem Christian-Doppler-Labor für "Metallurgische Grundlagen von Stranggießprozessen" am Lehrstuhl für Metallurgie der Montanuniversität Leoben wurden Heißrissseigerungen in Brammen und in Laborproben im Hinblick auf deren Entstehung und Auswirkungen auf die Produktqualität analytisch untersucht. Es wird gezeigt, dass die Konzentrationsanreicherung von Mangan in Heißrissseigerungen jene in Zentrumsseigerungen erreichen kann und die Ausbildung dieser in Bramme und Laborversuch weitgehend gleichwertig ist. Dies lieferte die notwendige Voraussetzung für die Übertragbarkeit der Ergebnisse aus dem Laborversuch in die Praxis.

Die Kenntnisse der Erstarrung des flüssigen Stahls zu festem Stahl sind wichtig für die Stranggießtechnologie. Die mathematische Simulation ist ein wertvolles Instrument, diese Aufgaben zu bewältigen. Die Erstarrung vom Meniskus bis zur Durcherstarrung wird simuliert. Die Information, die mit Simulation erhalten wird, dient als wichtige Basis für die Optimierung der Stranggießtechnik.

Bei der Erstarrung von Stahl in der Stranggussmaschine bildet sich ein Gussgefüge (Primärgefüge). Dieses Gussgefüge besteht aus primärausgeschiedenen Dendriten und der erstarrten Restschmelze (Mikroseigerung oder Kristallseigerung). Im Gegensatz zu den Mikroseigerungen bildet sich die Makroseigerung in der Brammenmitte und hat Auswirkungen auf das Endprodukt. Der Beitrag zeigt, dass es mehrere Möglichkeiten gibt, die Beurteilung der Makroseigerung (Mittenseigerung) durchzuführen: optische Beurteilung, Einzelfunkenanalytik (OES-PDA) und Elementverteilungsbilder mittels Mikrosonde. Eine Bewertung dieser Methoden wird dargestellt. Mittels dieser Methoden wurden die Wirkung der Soft Reduction auf die Mittenseigerung nachgewiesen und die Einstellungen optimiert.

The high energy irradiation causes significant structural modifications on the backbones of polymers. The radiation thermoluminescence method of investigation reveals the types of defects that are formed as electron traps. The recombination of released electrons with positive defects expels a quantum. The RTL intensity varies with temperature and distribution of gap depths. The difference between various sorts of polyolefins may be demonstrated by the position of maxima on the recorded glow curves.

Perfluorocarbon fluids, mainly C6F14 used as coolants within High Energy Physics Detectors in the Large Hadrons Collider (LHC) at CERN, were characterized by applying mainly the following methods: GC, FT-IR and UV-Vis. The aim of this work was the quality control, the identification and the quantification of different impurities which could increase the radiation sensitivity of these fluids. Thus, the presence of H containing molecules within perfluorocarbons strongly influences the appearance of hydrofluoric acid during their irradiation. The procedures settled-up in this work are sensitive to the presence of such impurities and would be used for the analyses of the received perfluorocarbon fluids as well as to assess the radiation induced modifications and the efficiency of their purification treatments. Geneva, Switzerland October 2006

The analysis reported compares the effects of different road conditions on the fatigue life of a transmission output shaft. Four routes having differing driving conditions were investigated and, of those routes, the route with most stop-start events resulted in the greatest reduction to fatigue life. In-vehicle loading data have been compared with shaft fatigue testing, indicating that the shaft should not fail by fatigue in service, despite a generous prediction of daily use. To introduce a theoretical failure, a load-scaling factor has been used, thus providing a factor enabling comparison of the routes.

The optical transparency of perfluorocarbons used as Cherenkov media is of prime importance to many Ring Imaging Cherenkov detectors. We will in this paper show that the main photon absorbers in these fluids are hydrocarbons with double or triple bonds. We will moreover discuss a process which can eliminate these pollutants and restore the intrinsic excellent optical transparency of these fluids in the VUV range.