Effect of semisolid casting process with cooling plate technique on microstructure and properties of high speed steel with high vanadium and carbon contents

Abstract

Semisolid metal processing with the cooling plate technique is one of the key technologies for producing advanced materials. The multitude of cast iron families with their wide range of mechanical properties and relatively low costs combined with the advantage of semisolid processing, give the merit of producing high quality cast components from cast iron. This research is based on high speed steel with high vanadium and carbon contents, which has not been studied enough. The authors researched the effect of semisolid casting with the cooling plate technique on microstructures and properties, wear resistance and mechanical properties, for example, hardness and tensile stress, of this alloy.     

Modelling of steel shrinkage and optimisation of mould taper for high speed continuous casting

Abstract

In high speed continuous casting, optimisation of mould taper is key for intensifying heat transfer and for improving the quality of the cast products. Mathematical modelling has been carried out by combining heat transfer, steel shrinkage and parabolic continuous taper model in order to optimise the mould taper profile. These models have been assembled to a set of software, the inputs of which include the steel grade, casting speed, casting temperature, length and the cross-section of mould tube, while the outputs consist of surface temperature of the strand, thickness of solidified shell, thermal linear expansion coefficient, steel shrinkage, distortion of the mould tube wall, the actual air gap, total taper and the continuous taper profile. Optimum mould taper has a parabolic profile which is tapered inwards that changes continuously along the length of the strand in order to achieve reduction in air gap while avoiding distortion of the mould tube.     

一种节能意识的多路径QoS保证路由协议

综合SPEED与SEEM协议,提出了一种混合型协议QoSDM。它针对多数QoS保证的路由协议没有特别考虑到无线传感器节点的能量约束的问题,在sink和多个源节点之间找到多条路径,减少碰撞的发生,利用多个节点代表源节点来接收和转发数据包。多径搜索使用的是全球网络知识,具有先进性。仿真结果表明,既保留了与SPEED相近的可靠性和时延性能,又具有SEEM多路径路由协议的节能QoS保证效率,展现了此协议的潜力和效益。这特别适合于高QoS要求情况下又需要节省能源消耗的情形,符合当前的研究趋势。     

INFLUENCES OF CASTING SPEED AND SEN DEPTH ON FLUID FLOW IN THE FUNNEL TYPE MOLD OF A THIN SLAB CASTER

In recent years, thin slab continuous casting technology has been widely used to improve the quality of the product and to reduce the cost. One of the challenges faced by this technology is to design reasonable flow patterns, which strongly affect the surface and inner properties of the final slab in the mold. With the fixed scales and complex geometrical structures of nozzle and funnel type mold, a series of numerical simulations are made to analyze the flow patterns in melt steel using finite volume method based on structured body fitted coordinate grids. The CFD （computational fluid dynamics） package is validated first using one typical case described in previously published studies, and then it is developed to study the effect of operational parameters on fluid flow in thin slab caster. Two operational parameters, casting speed and SEN （submerged entry nozzle） depth, are mainly considered for numerical analysis. On the basis of present simulations, the reasonable SEN submergence depths corresponding to different casting speeds are suggested according to fluid flow characteristics like, flow jet impingement on the narrow side of the mold, flow speed of the melt steel beneath the meniscus and the recirculation region. This is the first stage of study on the numerical analysis of the whole thin slab casting process with electromagnetic brake.     

Proposed method of determining ISO speed for opto-electronic cameras used in astronomy

Abstract

Many of the more specialised digital cameras produced for use with telescopes have no information provided to describe their sensitivity in terms of a recognised system, such as an ISO speed rating, whereas digital cameras supplied for pictorial imaging usually do have an ISO speed quoted by the manufacturer. The science of photographic sensitometry has become established over the past 110 years and, in many respects, the knowledge gained can be applied satisfactorily to non-photographic camera systems used for astronomy and also for many other scientific and technical applications. A method is described by which an ISO speed rating can be assigned to a digital camera system used for imaging in astronomy.     

Random nature of droplet size and its origins in short circuit CO2 arc welding

Abstract

The nature of the droplet size variation and its effect on the process behaviour were investigated for short circuit CO₂ arc welding using a power supply with constant voltage output. To obtain the droplet images and record the welding current and voltage transient waveforms in phase, an integrated experimental system was established by combining a high speed charge coupled device camera based on laser shadowing and a related optical system with a dual channel analog/digital converter. The droplet size in short circuit transfer mode is defined as the maximum diameter of the molten droplet just before short circuiting. The experimental results reveal that the distribution of droplet size typically has a random nature with a range of between 1 and 2 times the electrode diameter. Excessively large or small droplet size is markedly unfavourable to the process stability. The droplet shape just before short circuiting and the short circuiting experience are also critical factors affecting the process behaviour. The main factors influencing the droplet size and shape are analysed in detail and approaches to control their evolution are then proposed.     

Generation of compressive residual stresses by high speed water quenching

Abstract

According to the literature, rapid water quenching can create compressive residual stresses (RSs) near the surface and thereby produce a significant increase in the fatigue limit. This technique is called 'intensive quenching'. In the present paper, some results from a research project will be presented. The project was initiated by the technical committee 'quenching' of the German Heat Treatment Association to deal critically with this issue.

The focus of this paper is on the influence of the martensite transformation on RS generation. A process window was determined, within which one needs to quench fast enough, to get the surface temperature below the M_S temperature, before the maximum temperature gradient in a cylinder is reached, in order to get compressive RSs on the surface.     

Determination of macroinclusions during clean steel production

Abstract

There are very few macroinclusions in clean steel, but the few that exist are very harmful for material properties of the final steel product. To date, very little information on large, so called macroinclusions in clean steel production has been presented. Therefore, the present study has focused on providing information on these inclusions during different stages of the steelmaking process, based on plant trials carried out at Uddeholm Tooling, Hagfors, Sweden. Macroinclusion size distributions have been determined using optical microscopy and classified according to a modified version of the Swedish standard SS 111116, as well as using immersed ultrasonic scanning. For the sake of completeness, the size distribution of microinclusions has also been determined using optical microscopy. Inclusion compositions were determined using a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). Two types of liquid steel sampler were used in the investigation: a rapid solidifying (RS) sampler and the LSHR (liquid sampling hot rolling) sampler, suitable for immersed ultrasonic scanning. The results are critically discussed with respect to process conditions, such as alloy additions that took place during the plant trials.     

Fused deposition process combining electrochemical discharge with high speed selective jet electrodeposition

Abstract

Experiments have shown that the presence of a localised laser heat source significantly increases the deposition rate and deposit quality obtained by high speed selective jet electrodeposition (HSSJE). In this study, a relatively new process, fused deposition through electrochemical discharge (FDED), which uses heat generated by an aqueous electrochemical discharge in HSSJE, has been reported. The objectives of this investigation have been to identify the deposition mechanism and to compare FDED and laser-enhanced HSSJE with respect to deposition rate. During FDED, the nature of the deposited layer evolves with time, starting from a rough/dendritic layer to a powdery deposit at the top. Electrochemical discharge, depending on the voltage and standoff distance (SOD), can either fuse or erode the deposit. Experiments suggest that the metal deposition rate of 11 μg s^?1 in FDED is of the same order as laser-enhanced HSSJE. The desired objectives of a smooth, fully compact deposit and high deposition rates can be obtained by an optimum combination of electrolyte flowrate, electrode SOD, applied voltage and table speed.     

感受风的速度

接到约稿的通知,正忙得不可开交。第二天下午四点半,一档大型户外特别节目就要开始录制,我担任这个访谈节目的主持人,还有好些案头工作没有完成,加加班吧。“有班加是幸福的”,每次在疲惫之中总是给自己这样的鼓励。这种疯狂的工作状态虽然辛苦,但至少说明生活是充实的。