Evolving mechanism of eutectic carbide in as-cast AISI M2 high-speed steel at elevated temperature

AbstractThe evolution in type,size and shape of carbides in as-cast American Iron and Steel Institute(AISI) M2 high-speed steel before and after annealing were investigated.The micromechanism which was responsible for those changes was also analyzed and discussed.At the initial stage of reheating,metastable M2C-type carbide decomposed continuously.M6C-type carbide nucleated at the interface of M2C/γfirstly and grow from surface to center.Then MC-type carbide nucleated at both surface of M6C/M6C and inner of M6C.With the increasing decomposition of the metastable M2C-type carbide,the rod-shaped construction of eutectic carbide began necking,fracturing and spheroidizing gradually.Held enough time or reheated at higher temperature,particle-shaped product aggregated and grew up apparently,while secondary carbide precipitated in cell and grew up less sig- nificantly than the former.Based on the above microstructural observation,the thermodynamic mechanism for decomposition of M2C carbide,for spheroidization of products,and for the growth of particles were analyzed.The rate equations of carbides evolution were derived,too.It shows that the evolving rate is controlled by diffusion coefficients of alloy atoms,morphology of eutectic carbides and heating temperature.     

Research on electron beam welding of in situ TiB<Subscript>2p</Subscript>/ZL101 composite

Electron beam welding of in situ TiB_2p reinforced aluminum composites was studied. The results show that no obvious pores or cracks is presented in the weld seam. The grains in the weld seam are remarkably refined and TiB₂ particles distribute much more homogeneously than that in base metal. The hardness values of fusion zone and heat affected zone (HAZ) are both increased in comparison with that of base metal. There are no interface reactions between TiB₂ particle and Al matrix. This results supply the evidence that the novel TiB_2p reinforced aluminum composites can be well joined with the electron beam welding.     

HXN5型内燃机车空气管路系统

随着我国铁路运输事业向着高速、重载的方向迅速发展．对铁路列车制动技术提出了更高的要求。HXN5型内燃机车是戚墅堰机车有限公司与美国通用电器公司共同合作的,对HXN5型内燃机车空气管路系统的掌握和了解对机车的运用及检修均有很大的帮助。     

Rigid-flex coupling modeling and simulation on multistage gear transmission system

As multistage gear transmission systems are complex and precise, the flexibility of shaft can influence the dynamic response of system. In order to study dynamic response of the system, we build the rigid model of gear system and the finite element model of the gear shaft. The rigid-flex coupling model is established with the virtual prototype technology, and a contrast between rigid model and rigid-flex coupling model is constructed.With these methods, the dynamic responses with different rotation speeds and different loading magnitudes are examined. We also analyze the influence of shaft flexibility, rotation speeds and loading magnitudes on the vibration characteristics of gear transmission systems.     

Sybase复制服务器构造及其在客票系统中应用

作者介绍了Sybase数据库复制服务器11.5.x的新特性以及铁路客票系统应用Sybase复制服务器构造数据复制系统的情况.     

临沂市沂河大桥设计

本文对沂河大桥的设计作了简要介绍并对刚架拱桥、钢管混凝土系杆拱桥的设计与施工要点进行了浅述。     

提速道岔运用中存在的问题分析及措施

对提速道岔在济南电务段管修区段运用3年来存在的问题及原因进行了分析，提出了解决问题的相关措施和建议。     

确立地下铁道车站服务区规模的数学模型

土木工程的优化设计包括因素很多,本文用排队论的理论,对确定地下铁道车站服务区规模试探建立一个数学模型。     

徐家汇综合交通换乘枢纽与地下空间一体化开发利用

徐家汇是上海市最早启动建设、发展最快的城市副中心,是重要的市级商业中心和交通枢纽,轨道交通徐家汇枢纽是上海市轨道交通网络中唯一的一个三条市域线交汇的大型换乘枢纽。文章介绍了徐家汇轨道交通换乘枢纽实施方案:9号线利用既有地下室改造成车站,11号线车站设于拟建改造地块中,两条新建轨道交通线车站都避开了主要交通道路,很好地解决了车站实施对地区交通、商业和环境的影响,是轨道交通理念和实施技术的突破。文章还结合轨道交通换乘枢纽,提出了地下空间一体化概念和地下道路方案。     

钢索公路护栏的拦截性能研究

在汽车与公路护栏碰撞事故中,护栏不仅有拦截、导向作用,还要有良好的缓冲吸能特性,以减小由于乘坐空间过度变形以及人与车内物体二次碰撞对乘员的伤害。通过实车与钢索护栏的碰撞试验,研究了护栏、汽车和乘员的动态响应特性,结果表明,钢索护栏完全符合要求,可为高速公路护栏的设计、施工以及在不同地点的设置提供借鉴。