低碳马氏体在塑料模具中的应用

低碳马氏体渗碳型塑料模具钢 低碳钢、低碳合金钢模具在成形后进行渗碳、淬火和低温回火,使模具表面得到高碳细针状回火马氏体＋颗粒状碳化物＋少量残留奥氏体,心部组织主要为低碳马氏体。从而保证了模具表面具有高硬度（58HRC～62HRC）、高耐磨性,而心部具有较高的强韧性（30HRC～45HRC）,用于制造各种要求耐磨性良好、形状复杂、承受载荷较高的塑料成形模具。     

高强度螺栓连接钢结构的制作与安装

根据高强度螺栓连接钢结构的特点 ,提出保证质量、提高进度的制作方法和安装要点。     

高强度螺栓的表面处理与机械镀锌

介绍了高强度螺栓电镀锌工艺中,对氢脆的控制情况,以及适于标准件行业的消除氢脆失效的表面处理新方法-机械镀锌。这种方法为我国高强度标准的镀锌开辟了一条新的途径,能提高我国高强度标准件的市场竞争力,是一种表面处理的先进工艺。     

高强度螺栓在H2S环境下氢脆敏感性分析

对强度为10.9和12.9级的镀锌螺栓,分别进行除氢和不除氢工艺处理后使其在屈服应力值下,在H2S+NaCl条件下加载168 h,通过螺栓的断裂情况和断口分析可知12.9级的螺栓镀锌后有非常高的氢脆敏感性,而10.9级的螺栓镀锌后在H2S条件下没有发生氢脆断裂,这一结论对以后的生产有比较现实的指导意义.     

Mg—PSZ陶瓷热处理与四方析体马氏体相变温度关系的研究

采用带有液氮负温裝置的LK-02型高速淬火膨胀仪对已获得工业应用的、含10mol％MgO的Mg-PSZ陶瓷的热处理条件与其中t-ZrO_2的马氏体相变温度(M_4、M_6)及可相变t-ZrO_7析体量的关系进行了研究,认为:t-ZrO_2析体的粒径及其热处理过程中的应力应变状态是决定或影响马氏体相变温度高低和在应力诱导下可相变t-ZrO_2量的两个基本因素;采取1420℃和1100℃的综合热处理,与在1420℃或1100℃进行单一温度热处理相比,易于控制M、和M_4值,且能保证较高的可相变t-ZrO_7析体量,是优化Mg-PSZ结构和性能的一种值得进一步进行研究的热处理工艺。经1100℃、4b热处理的Mg-PSZ试样的“Δl-T”曲线的低温端未观察到明显的表征马氏体相变的膨胀效应。     

涂层石墨电极在冶炼低碳铬铁上的应用

1.前言涂层石墨电极是炭素制品中的一种,它具有耐高温抗氧化,比电阻低等特点,目前在钢铁冶炼方面应用已取得一定的经济效果。冶炼铁合金的电弧精炼炉过去使用石墨电极,消耗较大,今年试用了涂层石墨电极。涂层电极在铁合金行业冶炼低碳铬铁使用实践证明,涂层电极是目前降低冶炼铁合金用电极消耗最为有效的材料。     

低碳马氏体强化工艺在汽车板簧上的应用

近十多年来低碳马氏体强化工艺虽已在国内有较多应用,但在汽车板簧上应用还是一种尝试。1983年11月以来,我厂利用28MnSiB钢,采用低碳马氏体强化工艺,试制了美国联合发展有限公司(U.D.I)的E_3～1750型、09475—01型、466017C91—01型、E_6—4000型出口板簧。严品质量均达到美国“S.A.E”标准,疲劳寿命10万次未断,已于1984年6月开始销往美国。1.28MnSi 钢的强化用低碳马氏体强化工艺制作汽车板簧,工艺简单、容易掌握,可在原有的60Si_2Mn 钢生产线上生产。它的技术关键在于低碳马氏体的形成及强化,也就是说以淬火来得到低碳马氏体。钢的淬透性、含碳量,奥氏体化温度及淬火介质因素,     

内蒙古化肥厂H型钢结构中高强度螺栓连接的设计

简述 H型钢结构中的高强度螺栓连接的设计以及对高强度螺栓连接产生不利影响的因素及其处理方法     

螺栓拉伸器在设备检修中的应用

在尿素生产中,高压设备的密封保证正常连续生产的关键。本文重点阐述了螺栓拉伸器在高压设备的人孔,封头的预紧,热紧,拆卸中的应用。     

High purity multiwalled carbon nanotubes under high pressure and high temperature

We have studied the structural modifications that multi-walled carbon nanotubes (MWNTs) undergo when treated under high pressure and high temperature (HP-HT). Uniaxial pressures of 5.5-6.5 GPa were applied to samples of purified MWNTs between 850 and 950 °C for 30 min. The resulting material was then analysed by X-ray diffractometry, Raman spectroscopy and transmission electron microscopy. Comparison of the data obtained by such analyses before and after treatment does show changes in the Raman spectra, a slight linear decrease of the d₀₀₂ spacing, and some structural modifications that could be due to MWNT segmentation and interlinking.     

Synthesis and characterization of porous Y2SiO5 with low linear shrinkage,high porosity and high strength

The emerging porous Y₂SiO₅ ceramic is regarded as a promising candidate of thermal insulator owing to its very low thermal conductivity. However, recent works on porous Y₂SiO₅ are confronted with severe problems such as large linear shrinkage (18.51–20.8%), low porosity (47.74–62%) and low strength (24.45–16.51 MPa) at high sintering temperatures (1450–1500 °C). In this work, highly porous Y₂SiO₅ ceramic with low shrinkage and excellent high-temperature strength was fabricated by in-situ foam-gelcasting method at 1550 °C. The as-prepared sample has unique multiple pore structures, low linear shrinkages of 6.3–4.5%, controllable high porosities of 60.7–88.4%, high compressive strengths of 38.2–0.90 MPa, and low thermal conductivities of 0.126–0.513 W/(m K) (porosity: 87.1–60.2%). The effects of relative density on relative strength, as well as porosity on thermal conductivity were quantitatively discussed. The present results indicate that porous Y₂SiO₅ is the potential high-temperature thermal insulation material of light weight, low thermal conductivity, and high strength.     

Application of a high magnetic field in the carbonization process to increase the strength of carbon fibers

Carbon fibers produced from PAN (polyacrylonitrile) as a precursor are generally subjected to the three heat treatment processes of stabilization and carbonization followed by graphitization. Stabilized fibers were carbonized in a high magnetic field of 5 T imposed parallel to the fiber axis at a temperature of 1445 K and graphitized without a magnetic field at 2273 K. The tensile strength of these treated fibers is increased by 14% in comparison with those of no magnetic treatment. The reason why the imposition of the magnetic field could improve the strength of the fibers has been studied through microscopic observation of the fiber surface as well as a statistical analysis by use of Weibull distributions.     

Compressive strength of three-dimensionally reinforced carbon/carbon composite

Compressive behavior of three-dimensionally reinforced carbon/carbon composite (3D-C/C) was examined from room temperature to elevated temperatures up to about 3000 K. Three-dimensionally reinforced C/C was found to have an inclination to induce kinks at the ends of specimens due to extremely low shear strength. In order to avoid this type of premature fracture and to conduct high-temperature tests, discussion was made on specimen geometry and testing procedure, and the combination of a dumbbell-shape specimen and test configuration without a supporting jig were found to be suitable for the present study. Using this set-up, the compressive strength of a 3D-C/C was evaluated as a function of temperature up to about 3000 K. The compressive strength of the 3D-C/C monotonically increased with the increase in temperature up to 2300 K, but decreased above this temperature. The strength enhancement was suggested to be caused by improvement in the fiber/matrix interfacial bonding, and the degradation over 2300 K was by softening of the matrix at high temperatures.     

Adsorption enthalpies of sodium dodecyl sulphate onto carbon blacks in the low concentration range

Adsorption enthalpies of sodium dodecyl sulphate onto a set of carbon blacks from aqueous solutions in the low concentration range are presented. The surfactant was found to adsorb on the carbon surface exothermally in the whole studied coverage. From the calorimetric results and the analysis of the adsorption isotherms by a double Langmuir equation, a model of the adsorption mechanism in these systems is suggested. The adsorption of the surfactant onto the carbon blacks can be explained by two energetically distinct steps corresponding to the adsorption of SDS in two different types of porosity.     

Catalytic growth of macroscopic carbon nanofiber bodies with high bulk density and high mechanical strength

Carbon nanofibers (CNF) are non-microporous graphitic materials with a high surface area (100-200 m²/g), high purity and tunable surface chemistry. Therefore the material has a high potential for use as catalyst support. However, in some instances it is claimed that the low density and low mechanical strength of the macroscopic particles hamper their application. In this study we show that the bulk density and mechanical strength of CNF bodies can be tuned to values comparable to that of commercial fluid-bed and fixed-bed catalysts. The fibers were prepared by the chemical decomposition of CO/H₂ over Ni/SiO₂ catalysts. The resulting fibers bodies (1.2 μm) were replicates of the Ni/SiO₂ bodies (0.5 μm) from which they were grown. The bulk density of CNF bodies crucially depended on the metal loading in the growth catalyst. Over 5 wt% Ni/SiO₂ low density bodies (0.4 g/ml) are obtained while 20 wt% Ni/SiO₂ leads to bulk densities up to 0.9 g/ml with a bulk crushing strength of 1.2 MPa. The 20 wt% catalysts grow fibers with diameters of ∼22 nm, which grow irregularly in space, resulting in a higher entanglement and a concomitant higher density and strength as compared to the thinner fibers (∼12 nm) grown from 5 wt% Ni/SiO₂.     

Shear-controlled electrical conductivity of carbon nanotubes networks suspended in low and high molecular weight liquids

Controlling the electrical conductivity is a critical issue when processing material systems consisting of an insulating matrix filled with conductive particles. We provide experimental evidence that given shear rates result in specific conductivity levels in such different systems as high-viscosity carbon nanotube/polymer melt or low-viscosity carbon nanotube/epoxy fiber suspensions. The steady-state conductivities are independent of the initial state of the dispersion. The observed behavior is modeled phenomenologically by the competition between build-up and destruction of conductive filler network. A particle-level simulation of flowing fiber suspension also reflects the observed behavior. Our results show that properties of particulate suspensions can be controlled by steady shear. They should be considered to obtain reproducible properties in shear-based processing technologies as injection molding or resin transfer molding.     

Interaction of hydrogen with carbon coils at low temperature

Hydrogen was adsorbed on carbon coils under 10 MPa hydrogen gas at liquid nitrogen temperature. The equilibrium pressure of hydrogen desorbed from the as-grown carbon coils with an amorphous structure was three to four times greater than those of multiwall carbon nanotubes (MWNT) and active carbons (AC). The heat treatment of the carbon coils at 850 °C contributed to an increase in hydrogen adsorption by 20% compared to the as-grown carbon coils. On the other hand, the adsorption of hydrogen gas on the carbon coils decreased significantly after heat treatment at a temperature higher than 1000 °C due to formation of capsule-like carbon composed of 10-20 layers on the surface of the carbon coils.     

Structural changes in carbon aerogels with high temperature treatment

The structural change of carbon aerogels at high temperatures up to 2800°C has been investigated. Change in microtexture of fine particles, which constitute carbon aerogels derived from phenolic resin, was of a typical non-graphitized carbon. The microporosity decreased with an increase of heat-treatment temperature, and disappeared at 2000°C. The mesoporosity still remained even after heat-treatment up to 2800°C, though 50% of mesopore volume was lost because of the fusion of the particles with the change of carbon microtexture.     

Nanoplates forced alignment of multi-walled carbon nanotubes in alumina composite with high strength and toughness

Although the strengthening and toughening effects on ceramic composites are expected to be maximized by alignment of multi-walled carbon nanotubes (MWCNTs) in matrices, this concept has been rarely realized in practice due to the lack of convenient processing strategy. Here, the alignment of MWCNTs in alumina composite can be readily obtained by using α-Al₂O₃ nanoplates as raw powder. With the assistance of vacuum filtration and pressure in sintering, the highly aligned MWCNTs in alumina matrix are formed in in-plane direction. Accordingly, the strength and toughness in 1.5 wt% MWCNTs/alumina composite are improved by 58 % and 66 % with respect to monolithic alumina, respectively. Transmission electron microscopy observation reveals that the MWCNTs under great compressive residual stress are mainly embedded inside the grains, leading to much stronger grain boundaries. Meanwhile, the toughening effect is mainly attributed to the highly energy dissipating bridging and pullout, owing to the very effective load transfer.