Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process

DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quench-ing temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the tem-perature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.     

Microstructural characterization of as-cast and homogenized 2D70 aluminum alloy

The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds (Al2CuMg, Al2Cu, Al9FeNi, Cu2FeAl7...     

Experimental study on Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the ferrite region

A Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied.Subsequent cold rolling and continuous annealing processes were also conducted.The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites.The yield strength,ultimate tensile strength,n value,and r value of the No.2 specimen hot-rolled in the ferr...     

灰色线性回归组合模型在计算给水管道阻力系数中的应用

为了求解管道阻力系数,将其应用到工程中的水力计算中,运用灰色线性回归组合模型进行求解,得出了计算管道阻力系数的数学模型,并结合工程实例进行验证.实践表明该模型的精度较高,具有一定参考价值.     

Research on indoor experimentation of range SAL imaging system

By means of advantages of both SAR and lidar, the combination of the techniques of (inverse) synthetic aperture and lidar makes it possible to obtain high resolution 2-D image. In this paper, an indoor experimental system of inverse synthetic aperture lidar imaging is given and a processing approach is presented. The given system is in the mode of lidar system with separated receiver and transmitter, which can effectively eliminate the jamming from the lens or/and the intersection between two optic fibers. ...     

一种改进的异步电动机直接转矩控制方法

针对传统异步电动机直接转矩控制方法转矩及磁链脉动大、开关频率不固定的缺点,提出了一种改进的异步电动机空间矢量调制直接转矩控制方法。该方法通过转矩角闭环控制实现定子磁链幅值和相角的解耦,从而获得参考电压空间矢量,实现对磁链误差和转矩误差的控制。仿真结果表明,该方法有效地克服了传统直接转矩控制方法的缺陷,获得了良好的动态响应性能。     

带初始材性缺陷梁加固后力学模型研究

既有混凝土结构难免存在带有初始材性缺陷的 ＲＣ构件,其加固可行性及力学行为与正常混凝土构件不同,当前缺乏针对性研究成果。为此,采用玄武岩纤维（ＢＦＲＰ）布加固了 2根混凝土材性不符合设计要求的 ＲＣ梁,另有 1根未加固梁作为对比梁,共计测试了 3根梁。通过试验加载观察缺陷梁在加固前后的受力特征、破坏模式和极限抗弯承载力,分析相应的力学模型,最后根据极限状态下的破坏模式,采用“系杆 －拱”模型推导出缺陷梁加固后极限承载力计算公式。结果表明:随着外荷载和破坏程度的增加,加固梁由正截面抗弯模型进化到“梳状拱”受力模型,再变为极限状态下的“系杆 －拱”模型;梁底 ＢＦＲＰ布加固结合梁端 Ｕ型锚固措施可以有效提高缺陷梁的抗弯刚度、屈服荷载和极限承载力;提出的承载力计算公式计算值和试验值吻合良好且适中保守。     

隧道复合式路面动力响应影响因素的权重分析

为揭示车辆荷载作用下公路隧道复合式路面结构力学响应,依托实体工程开展现场试验,采用有限元软件建立三维有限元模型并进行模型精度验证,分析车辆荷载、路面结构尺寸以及材料参数对有仰拱和无仰拱的隧道复合式路面动力响应的影响。结果表明:隧道复合式路面混凝土面层最不利荷载位置为纵缝边缘中部,轴载和混凝土面层厚度对混凝土面层板板底拉应力、沥青层层底拉应变以及层间剪应力的影响较大,水平荷载和混凝土面层模量对各项动力响应指标的影响较小;普通复合式路面沥青面层动力响应隧道路面相差较小,混凝土面层板底拉应力分别为有仰拱的 5．99倍、无仰拱的 1．74倍。研究结果可为隧道复合式路面结构设计方法研究提供参考。     

缓冲材料砌块不同组合形式长期性能演化研究

高水平放射性废物地质处置库中缓冲层由缓冲材料砌块堆砌组成,层内不同类型的砌块接缝导致砌块存在不同的组合形式。采用 ＬＡＧＡＭＩＮＥ软件,对缓冲材料砌块 6种不同组合形式进行计算,分析了不同组合形式的温度、饱和度和膨胀力随时间的变化规律。缓冲材料温度在开始 10年内均低于100℃,之后明显降低,到 100年时均低于 35℃,1000年时废物罐释放的热量基本可以忽略不计;砌块内接缝数量越多,完全饱和用时就越短,水化1350天后,所有砌块组合形式内部均完全饱和;随着径向接缝增加,缓冲材料饱和越快,外环接缝附近优先出现膨胀力极大值;砌块中的径向和环向接缝使膨胀力最大值明显下降,且径向接缝的影响大于环向接缝,2000年后,缓冲材料膨胀力趋于稳定。     

基于 Ｏ-Ｋ算法的边坡位移时空演化规律研究

传统的位移监测方案通常以对单一点位的监测数据为基础。在对测量结果的评估中,也只考虑单一点位的数据变化情况,而忽略各监测点间监测数据的空间效应。以南京地区某边坡的自动化位移监测数据为依托,通过引入普通克里金（Ｏ-Ｋ）空间插值技术,运用 Ｍａｔｌａｂ平台自主研发了边坡位移时空演化规律分析模块,实现了对目标边坡位移时空演化过程的分析。该模块可以将位移插值误差控制在 5％范围之内,在部分监测数据缺失的情况下,解决了基于实测数据的边坡位移时空演化规律分析问题。