回火工艺对热轧高强贝氏体钢轨组织和力学性能的影响

本文研究了不同回火工艺条件下热轧态U25CrNi高强贝氏体钢轨的组织与力学性能变化。结果表明,试验钢热轧态和回火组织均由贝氏体、马氏体和残余奥氏体构成。当回火条件为300℃×200min时,试验钢中部分残余奥氏体发生贝氏体相变,钢的各项力学性能变化不大;当回火温度升至400℃时,试验钢中残余奥氏体体积分数较大,碳化物析出量较少,内应力进一步释放,试验钢的延伸率和冲击吸收功达到最大值,同温度下延长回火时间至360min,钢中碳化物颗粒析出增多,延伸率和冲击性能明显降低;当回火温度为500℃时,试验钢中贝氏体铁素体明显粗化,并伴随大量碳化物颗粒析出,残余奥氏体大量分解,出现了回火脆性。综合考虑,U25CrNi热轧高强贝氏体钢轨的最佳回火工艺为400℃×200min。     

回火温度对1500MPa级直接淬火钢组织与性能的影响

设计了一种新型1500MPa级Si-Mn-Cr-Ni-Mo多组元系低合金、超高强度工程结构钢,研究了回火温度对直接淬火钢组织与力学性能的影响.结果表明,抗拉强度随回火温度的升高而不断降低,屈服强度随回火温度升高先升高后下降,延伸率和冲击功均随回火温度升高呈现先升高、后降低、再升高的变化趋势.分析认为,回火过程组织演变的物理机制一方面包括板条马氏体和位错亚结构的回复、再结晶软化过程,另一方面包括残余奥氏体的分解与马氏体中过饱和碳的脱溶及析出第2相的强化机制综合作用.250℃回火后,板条马氏体内析出ε碳化物;400℃回火后ε碳化物明显粗化,产生回火脆性;600℃回火后部分析出相在奥氏体中形核,在马氏体基体内长大和粗化,最终形态为近似球形,另一部分析出相在马氏体内形核、生长,呈现椭球形或矩形.     

低碳Si-Mn系DQ&P钢组织演变模拟研究

以低碳Si-Mn钢为研究对象,采用直接淬火-配分工艺,研究了不同变形温度和配分时间对组织演变行为的影响.结果表明,QP钢典型组织由马氏体、铁素体和少量残余奥氏体组成.其中马氏体呈现板条马氏体、孪晶马氏体等特征.随着配分时间的延长,显微组织呈现回火转变趋势.当变形温度为950℃和880℃时,残余奥氏体体积分数先增加后减少,均在配分150 s时达到最大值,分别为9.1%,10.1%.当变形温度在820℃时,由于先共析铁素体的存在易于获得较多的残余奥氏体,体积分数高达11.9%,并且残余奥氏体中平均碳含量相对较低.     

一步淬火分配钢的工艺设计与微观组织演变

设计并研究了低碳硅锰系淬火分配(Q&P)钢的热处理工艺.利用SEM,TEM和XRD观察并分析了实验钢的微观结构和相组成.理论计算结果显示:Fe-021C二元合金的最佳淬火温度为290℃,最大残余奥氏体含量(摩尔分数)为179%.工艺模拟结果表明:实验钢残余奥氏体体积分数为67%~172%,残余奥氏体平均碳质量分数为102%~148%.残余奥氏体与相邻马氏体板条间晶体学位向符合K-S关系或N-W关系.实验所涉工艺中均存在新鲜马氏体的生成.随着配分时间的延长,残余奥氏体含量先增加后减少,残余奥氏体平均碳含量不断增加,最佳配分时间为50s.配分后期马氏体板条中出现的碳化物导致了残余奥氏体的减少.     

低碳Si-Mn钢直接淬火-等温配分工艺中组织演变

以低碳Si-Mn钢为研究对象,在传统淬火-配分工艺中引入压缩变形,研究了压缩变形对组织演变的影响以及实验钢在不同等温配分条件下的显微结构特征.结果表明,引入高温变形处理后,试样具有更加精细的显微结构,同时显微组织中含有较高比例的大角度晶界,由无变形条件下的65.7%提高至72.5%;在相变及碳配分过程中,晶界以及板条边界附近易形成碳富集区;随配分时间延长,显微组织呈回火转变趋势,当配分时间延长至1 500 s时,组织中出现较大量的碳化物析出相,残余奥氏体体积分数降低至7.9%.     

调质低碳贝氏体钢的组织和性能

研究了C--Mn--Mo--Cu--Nb--Ti--B系低碳微合金钢915℃淬火和490～640℃回火的调质工艺对钢的组织及力学性能的影响.用扫描电镜和透射电镜对实验钢的组织、析出物形态和分布以及断口形貌进行观察,采用X射线衍射仪分析钢中残余奥氏体的体积分数.结果表明:调质后,实验钢获得贝氏体、少量马氏体及残余奥氏体复相组织,贝氏体板条宽度只有250 nm,残余奥氏体的体积分数随着回火温度的升高而降低,经淬火与520℃回火后残余奥氏体的体积分数为2.1%.调质后析出物的数量激增,6～15 nm的析出物占70%以上.实验钢经过915℃淬火与520℃回火后,其屈服强度达到915 MPa,抗拉强度990 MPa,-40℃冲击功为95 J.细小的析出物及窄的板条提高了钢的强度.板条间有残余奥氏体存在,改善了实验钢的韧性.     

亚稳奥氏体对高强度海洋工程用钢力学性能的影响

采用力学性能测试、组织观察等方法研究临界退火和不同温度回火对海洋工程用钢显微组织和力学性能的影响.结果表明,实验钢经两相区退火和不同温度回火后,获得了回火马氏体及不同体积分数(0~6%)的残余奥氏体.随实验钢中残余奥氏体体积分数的增加,屈服强度从753MPa降低到506MPa,抗拉强度介于794~843MPa,屈强比从0.9降低到0.6,延伸率从31.3%提高到36.2%.实验钢中残余奥氏体能够提高冲击塑性变形能力并阻碍裂纹扩展,在-80℃冲击功达到236J,然而热稳定性差的残余奥氏体在低温下优先转变成马氏体并降低了低温韧性,冲击功下降到136J.     

Fe-Mn-1.6 Ni-C水电用钢板轧后 直接淬火和回火工艺

通过Fe-Mn-1.6Ni-C钢板控制轧制、轧后直接淬火和560~710℃回火调质处理实验,研究了轧后直接淬火态和回火态的组织与性能变化.结果表明,轧后直接淬火得到组织细小的板条马氏体,固溶强化作用提高了其抗拉强度.经过回火热处理后,碳化物的析出及其对位错的钉扎作用,降低了钢的抗拉强度,提高了钢的屈服强度.随着回火温度的升高,碳化物聚集长大,铁素体发生回复与再结晶,造成强度下降以及冲击韧性提高.当回火温度高于A_○c1时,粗大的碳化物极易引起裂纹形核,破坏钢的冲击韧性.Fe-Mn-1.6Ni-C钢最优的回火温度为680℃,屈服强度为963MPa,抗拉强度为988MPa,延伸率为20.0%,-60℃冲击功为142J.     

65Nb钢冷镦模具回火组织变化与耐磨性的关系

基体钢(65Nb)冷镦模具经超低温工艺处理后微观组织发生了变化,即从回火马氏体中析出碳化物微粒,残余奥氏体转变成马氏体并析出微细碳化物。这种组织变化可显著提高模具的耐磨性和冲击韧度,因而也大大延长了模具的使用寿命     

细小弥散碳化物与回火马氏体脆性

本文利用透射电子显微镜及物理化学相分析技术研究了中碳硅—锰钢中回火马氏体脆性(TME)的微观机制,着重探讨了回火过程中析出的碳化物对TME的作用。结果发现,对应于40Si2Mn2钢中TME产生的回火温度区间,存在有由碳化物向渗碳体的转变,析出了细小弥散的颗粒状渗碳体。这种对应现象在40Si2Mn2Mo钢中也得到证实。40Si2Mn2Mo钢的TME产生的回火温度和弥散渗碳体的析出温度都要高于40Si2Mn2钢。由此得出:在回火过程中大量细小弥散渗碳体的析出是中碳硅—锰钢中TME产生的一个重要原因。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to