Effect of cooling rate on solidification structure and linear contraction of a duplex stainless steel

Cooling rate is a key factor that can drastically affect the phase transformation and thermal stress of duplex stainless steels. Therefore, in this research, different sand moulds were used to explore the influence of cooling rate on the solidification of the 2304 duplex stainless steel (DSS). The macro and micro structures of the 2304 DSS were investigated. Small equiaxed grains are obtained in chromite sand mould sample with a lower pouring temperature and a higher cooling rate, whereas coarse columnar and equiaxed grains are found in silica sand and refractory powder mould samples. The size of austenite phase is significantly increased with decreasing cooling rate, while the ferrite phase content ranging from 51.6% to 53.9% does not change obviously. In addition, the linear contraction of the 2304 DSS decreases from 2.34% to 1.09% when the mean cooling rate above 1,173 K increases from 0.99 K·s-1 to 3.66 K·s-1.

Crustal electric structure of Haiyuan arcuate tectonic region in the northeastern margin of Qinghai-Xizang Plateau, China

Through the analysis and 2-D inversion for the 5 profiles in Haiyuan arcuate tectonic region (105°-107°E, 36°-37.5°N) in the northeastern margin of Qinghai-Xizang Plateau, we have obtained the electric structure within a range of 160 km in width (east-west) and 60 km in depth in the studied area. The results show that the crustal electric structure can be divided into 6 sections, corresponding respectively to Xiji basin (I), Xihuashan-Nanhuashan uplift (II), Xingrenbu-Haiyuan basin (III), Zhongwei-Qingshuihe basin (IV), Zhongning-Hongsibu basin (V) and west-margin zone of Ordos (VI) from the southwest to the northeast. The crustal electric structure is characterized by a broom-shaped pattern, which scatters to the northwest and shrinks to the southeast. The structures in the top part of Haiyuan arcuate tectonic region are complete and large, however, they diminish from the arc top to the northwest and southeast ends. In the depth from 0 km to 10 km, the resistivity is high in the sections II and VI, but relatively low in the other four sections, showing a similar pattern of basin depression. The electrical basement in the section III is the deepest, displaying a dustpan shape that is deep in the southwest and shallow in the northeast. A series of discontinuous zones with high conductivity exist in the middle-lower crust in Haiyuan arcuate tectonic region, which is possibly related to the moderate and strong earthquakes in the region. The resistivity distribution in the focal area of the 1920 Haiyuan earthquake is significantly heterogeneous with an obviously high conductivity zone near the hypocenter regime.

Cenozoic Tectonic Evolution of the Arcuate Structures in the Northeast Tibetan Plateau

The northeast Tibetan plateau contains important inlbrmation on the northeastward growth of the Tibetan plateau. It is bounded by the Ordos Block to the east, the Alxa Block to the north, and the Tibetan Plateau to the south （inset in Fig. 1; Tapponnier et al., 2001）, and has undergone complex intracontinental deformation during the Cenozoic. In this region, the northeast-convex arcuate structures developed northeastward, and are composed of a series of Cenozoic NW-SE-trending basin-and-range terrain, i.e., the Haiyuan-Xingrenbu basin, Tongxin basin and Hongsipu basin, the Yueliang Shan-Nanhua Shan- Huangjiawa Shan, Xiang Shan-Xiangjing Shan, Yantong Shan and Luo Shan-Niushou Shah, which is geometrically similar with the American basin-range tectonics.

The Arcuate Nappe Structure on the Northern Margin of the Wuliang Moutnains in Western Yunnan

The arcuate nappe structure on the north edge of the Wuliang Mountains in westernYunnan Province is a complex nappe structural system with multiple superimposed structures.The autochthonous system is a WNW-trending arcuate fold belt consisting of the Jurassic andCretaceous and the allochthonous system is mainly composed of Upper Triassic rocks. Generally,the nappe structure moved from south to north, with the hanging wall thrusting in a WNW direc-tion for a distance of over 10km. The deep nappe structural system was formed at depths ofabout 5-10km in an environment not exceeding the greenschist facies. It occurred in theOligocene (about 40-20 Ma).

FATIGUE FRACTURE BEHAVIOR OF LOW CARBON MARTENSITE AND MARTENSITE/BAINITE DUPLEX STRUCTURE IN STEEL 20CrMnMo

Fatigue crack propagation rate,da/dN,and threshold stress intensity range,ΔK_(th),of steel 20CrMnMo containing low carbon martensite or low carbon martensite/bainite(LCM/B) duplex structure,obtained by oil quenching and austempered at 360℃,have been measured using specimens under four-point bending.Observation was also made of the crack path and fracture morphology with relation to microstructure.The formation of LCM/B duplex structure,which caused by 20% lower bainite after short-time isothermal treatment,may re- markably increase ΔK_(th)and considerably decrease da/dN.The effect of microstructure on da/dN and ΔK_(th)was discussed with the emphasis on the crack propagation path.

FATIGUE BEHAVIOUR OF M/B DUPLEX STRUCTURE IN A HIGH CARBON Cr-Mo-W STEEL

Determination was carried out of fatigue crack propagation rate of steel 65Cr5Mo3W2VSiTi (LM2)with various bainite contents and M/B duplex structure tempered at various tempera- tures.The threshold value of fatigue for each processing was estimated by experimental data. The mechanism for fatigue crack propagation of M/B duplex structure in steel LM2 seems to be non-continuous.The calculated fatigue crack micro-propagation rates are found to agree with the experimental data.

Deformation Mechanism of Bimodal Structured 2205 Duplex Stainless Steel in Two Yield Stages

A kind of micro/nanostructured 2205 duplex stainless steel(DSS)with uniform distribution of nanocrystals was prepared via aluminothermic reaction method.The analysis of stress-strain curve showed that the fracture strength and elongation of the specimen were 946 MPa and 24.7%,respectively.At present,the research on microstructure of bimodal 2205 DSS at room temperature(RT)mainly depended on scanning electron microscope(SEM)observation after loading experiments.The test result indicates that there are two different yield stages in stress-strain curve of specimen during tensile process.The microstructure of duplex bimodal structured stainless steel consists of two pairs of soft hard regions and phases.By studying deformation mechanism of bimodal structured stainless steel,the interaction between soft phase and hard phase are discussed.The principle of composition design and microstructure control of typical duplex stainless steel is obtained,which provides an important research basis for designing of advanced duplex stainless steel.

Re-discussion on the Jiaochang Arcuate Structure, Sichuan Province, and the Seismogenic Structure for Diexi Earthquake in 1933

The Jiaochang arcuate structure is one of the numerous arcuate structural belts in Sichuan. The present paper gives a further argument about the characteristics of that arcuate structure and the new activity of the Songpinggou fault and affirms that the Songpinggou fault is an active fault in the Holocene epoch. The Diexi M 7.5 earthquake took place in 1933 on the west wing of that arcuate structure, near the apex of the arc. Many authors have given quite different opinions about the genetic structure of that earthquake. The authors have made on the spot investigations time and again over recent years. Besides this, the authors have also further studied the shape of intensity contour lines, the distribution characteristics of ground surface seismic hazards, the left lateral dislocation of buildings along the Songpinggou fault, the NW trending ground fissures that developed on the ground surface after earthquake, and so on. On this basis, it is still considered that the seismogenic fault of the 1933 Diexi M 7.5 earthquake was the Songpinggou fault on the west wing of the Jiaochang arcuate structure.

Fabrication of high-strength duplex nanoporous Cu by dealloying a dual-phase Mg-Cu precursor alloy

Duplex nanoporous Cu was successfully fabricated by dealloying a dual-phase Mg-Cu precursor alloy consisting of intermetallic Mg2Cu and MgCu2.The duplex nanoporous Cu with embedded nanoporous struts exhibited highly enhanced strength compared to the typical monolithic nanoporous Cu under both compressive and flexural test conditions at room temperature;the duplex np-Cu sample exhibited a 12 times higher compressive strength and a 40 times greater flexural strength than the monolithic np-Cu sample.Factors responsible for the strength enhancement in the duplex nanoporous Cu are discussed.

Time-Hopping Sequence Design for Virtual Full Duplex via Rapid On-Off-Division Duplex

To achieve virtual full-duplex(VFD)communication using half-duplex radios,the rapid on-off-division(RODD)technique has been proposed in recent years.The time-hopping(TH)sequence is critical to controlling self-interference introduced in the paradigm.By constructing the collision model with a symbol level time scale,the periodic collision correlation function properties are introduced as the performance metric for the TH sequence in the RODD system.To achieve the best VFD performance,an optimization-based method for TH sequence design is proposed.In addition,the conventional TH frame structure design for RODD system is improved.Numerical simulations are presented to demonstrate that the proposed approach can significantly increase system performance.Results indicate that the TH sequence design is very effective for the RODD system.

Structural Study of Methylated and Non-Methylated Duplexes by IR Fourier Spectroscopy

Structure of the duplex consisting of 23 pairs of bases was studied before and after the methylation of two cytosine molecules from different chains of the duplex. The study was performed in a buffer solution using an IR Fourier spectrometer. The absorption bands corresponding to the duplex backbone were found to change their characteristics after the methylation. Firstly, the integrated intensity ratio of the absorption bands, S1044/S1085, decreased by a factor of 1.5. The absorption band at 1044 cm-1 corresponds to the COC bond of deoxyribose, and the band at 1085 cm-1 to the PO2symm.vibr bond. Secondly, a substantial shift of the absorption band 1085→1112 cm-1 (Δν = 27 cm-1) was observed. In addition, pronounced changes in the absorption region of CH stretching vibrations took place. In particular, shifting of some absorption bands assigned to the stretching vibrations of CH bonds;the 2979→2945.7 shift was equal to 33.3 cm-1. In addition to the indicated changes, some bands corresponding to the Z structure appeared in the methylated duplex. Thus, methylation of two cytosine molecules in the duplex leads to the order→order structural transition, most likely to the B→Z transition.

引信用双工形压电驱动器的设计及其驱动特性

为实现引信安全系统状态的恢复功能,满足引信全域安全控制的需求,提出了一种双工形压电驱动器应用于机电安全系统中。首先,参考双足式压电驱动器并根据设计要求对双工形压电驱动器进行了结构设计,并分析了其工作机理。然后,对设计的双工形压电驱动器进行了结构优化,基于优化结果给出驱动足的运动轨迹方程,保证了驱动足形成类椭圆运动轨迹。接着,搭建了实验平台对双工形压电驱动器样机进行驱动特性测试分析,确定了最佳工作频率,并得到了双工形压电驱动器往返运动速度和激励电压峰峰值的关系曲线。最后,针对引信高冲击工作环境,提出双工形压电驱动器抗高过载措施,并对压电驱动器进行抗高冲击过载实验。结果表明:压电驱动器的运动速度与激励电压峰峰值呈正相关,且在频率为130 Hz的激励电压作用下,压电驱动器的运动速度最佳;双工形压电驱动器在20 kg冲击载荷作用下仍能正常工作,验证了抗高过载措施的有效性。进一步验证了双工形压电驱动器实现引信安全状态可恢复功能的可行性。

Designing gradient nanograined dual-phase structure in duplex stainless steel for superior strength-ductility synergy

Similar to other metallic materials,duplex stainless steel dramatically loses its advantage of high ductility as they are strengthened.Here,we produce a gradient nanograined dual-phase structure in the 2101 duplex stainless steel,thus facilitating a superior strength-ductility synergy:a yield strength of 1009.5 MPa being two times higher than that of the as-received sample,a total elongation of 23.4%and a uniform elongation of 5.9%.This novel structure is produced through a processing route of ultrasonic severe surface rolling and annealing,which realizes a superposition of gradient nanostructure and lamellar dual-phase structure with austenite and ferrite.During the tension deformation of gradi-ent nanograined dual-phase structured duplex stainless steel,a significant accumulation of geometrically necessary dislocations occurs.These dislocations are formed to accommodate the deformation incompat-ibility caused by the layer-by-layer difference in strength and hardness of individual phase domains,as well as the inherent difference in properties between the austenite and ferrite domains.This results in a stronger hetero-deformation induced strengthening and hardening significantly contributing to superior mechanical properties.Our study provides a new avenue to develop advanced steels with high strength and ductility.

FeCrNi(AlTi)_(x)双相中熵合金的组织结构及其力学性能

采用真空悬浮感应熔炼法制备了FeCrNi(AlTi)_(x)(x=0、0.2、0.34和0.49)双相中熵合金,研究Al和Ti含量变化以及均匀热化处理对合金微观结构和力学性能的影响。结果表明:随着Al、Ti含量的增加,合金的相结构由FCC单相结构转变成FCC和BCC的双相结构,且随着Al、Ti含量的增加,BCC相的体积分数明显增加,合金的压缩屈服强度和硬度显著增加。均匀化热处理之后,FeCrNi(AlTi)_(0.2)合金的屈服强度和极限抗拉强度分别达到了519和852 MPa,伸长率提升到了17.2%,均匀化热处理使得铸态合金中部分元素的偏析能够均匀分布在基体中,从而实现了合金的强度和塑性的同步提升。

CE3MN双相不锈钢铸件裂纹成因与预防

针对30″-300 Lb上装式球阀阀体用CE3MN铸造超级双相不锈钢材质,利用FactSage8.2热力学计算软件以及FSstel钢铁数据库,并结合光学显微镜、扫描电镜和能谱仪以及X射线衍射仪等试验手段,研究分析了CE3MN材质铸件在固溶处理之前切割铸态冒口时所产生的裂纹原因。结果表明:CE3MN铸件在脆性相析出的敏感温度范围以内缓慢加热或缓慢冷却过程中,由于铸造成分偏析严重而产生大量富Cr、Mo的有害金属间化合物σ相,主要以短棒状、细针状弥散分布于铁素体基体内或以长链状、条带状、珊瑚状、(σ+γ_(2))胞状以及魏氏组织长针状等形式分布于α/γ相界处。生产实践表明:在气割CE3MN铸件冒口之前,毛坯预先进行固溶处理以消除铸态脆性σ相,抑制裂纹形成和扩展,或者利用锯床先冷锯切铸态冒口后再进行固溶处理,可从根本上规避产生裂纹的温度因素。

帕米尔东北缘及塔里木盆地西北部弧形构造的扩展特征

归纳了帕米尔东北缘弧形构造的基本特征 ,分析了塔里木盆地西北部EW向逆断裂背斜带与NNW向隐伏走滑断裂之间的关系。通过塔里木盆地与西南天山和帕米尔东北缘变形特征的对比 ,认为塔里木盆地西北部的变形样式与帕米尔东北缘的弧形构造类似 ,弧形构造具有由帕米尔东北缘向塔里木盆地扩展的特征 。

塔里木西南缘(齐姆根弧)前陆构造及形成机理

在对齐姆根弧形构造地表地质构造和深部地球物理资料综合分析的基础上 ,阐述了齐姆根弧形构造的几何学、运动学和分段性 ,提出了齐姆根弧形构造由依格孜牙薄皮推覆构造段、齐姆根主弧形三角带构造段和叶尔羌—棋盘对冲构造段组成 ,各弧形构造段之间以横向走滑—斜冲断层为界 ;发现了齐姆根弧形构造中规模巨大的塔里木西南盆地白垩系—新生界沉积盖层向西昆仑—帕米尔被动反 (逆 )冲逆掩构造系统 ,阐述了齐姆根主弧形构造段由铁克里克主动逆冲推覆系统、塔里木西南盆地被动反冲逆掩系统和深部双重构造组成。齐姆根弧形构造的隆升时期为喜马拉雅运动 ,新生代 。

中国西南思茅地体中部白垩纪古地磁结果及陆内地壳变形特征

对我国西南地区思茅地体中部巍山和五印地区白垩纪地层进行了详细的岩石磁学和古地磁研究,获得了两个地区的高温剩磁分量并通过了褶皱检验.巍山剖面特征剩磁方向为Ds=64.3°,Is=48.5°,k=54.6,α95=4.7°;五印剖面特征剩磁方向为Ds=15.4°,Is=44.8°,k=212.0,α95=4.6°.通过思茅地体磁偏角变化与兰坪—思茅褶皱带构造线迹变化的相关性分析,确定思茅地体内部差异性旋转变形受控于思茅地体弧形构造带的形成和演化.通过青藏高原东南缘走滑断裂带活动年代分析,确定兰坪—思茅褶皱带蜂腰构造部位形成于两期构造事件,早期构造变形与东喜马拉雅构造结北北东向挤压缩进有关,后期构造变形与川滇微地块发生顺时针旋转时南向挤出运动有关.以华南板块稳定区白垩纪古地磁极为参考极,计算得出巍山和五印相对于华南板块分别发生了10.5°±6.0°和3.8°±4.9°的南向运移量.通过选取思茅地体内部构造形态较稳定的巍山和普洱地区白垩纪古地磁极为参考极,计算得出五印相对于巍山和普洱分别发生了3.4°±5.0°和3.1°±5.4°的北向纬向运移,表明五印和和巍山之间自印亚碰撞以来经历了较大规模的北向地壳缩短变形作用.

鄂尔多斯盆地西缘古生代槽台过渡带裂谷系弧形构造带的形成与发展及对油气聚集富集规律的影响

在稳定的鄂尔多斯盆地西缘槽台过渡带地区古生界弧形裂谷系的发育、发展推动下,地块形变成南北成带、东西分区、隆洼相间的弧形构造带,并控制了油气分布规律,经后期盆山转换和耦合,这种变形至今对鄂尔多斯盆地油气勘探方向仍有重要参考意义。

青藏高原东北缘海原弧形构造区地壳电性结构探测研究

对青藏高原东北缘海原弧形构造区(105°～107°E,36°～37.5°N)的5条大地电磁测深剖面进行处理分析和二维反演,得到研究区内东西宽约160km、深约60km范围的地壳电性细结构.结果表明:研究区呈现南西—北东的带状分布特征.由南西—北东可分为6个电性区块,依次为西吉盆地(Ⅰ)、西、南华山隆起(Ⅱ)、兴仁堡-海原盆地(Ⅲ)、中卫-清水河盆地(Ⅳ)、中宁-红寺堡盆地(Ⅴ)和鄂尔多斯西缘带(Ⅵ).各区块在平面上呈北西撒开、南东收缩的“扫帚状”形态;弧形构造区弧顶附近构造完整、规模大,自弧顶向北西、南东两端构造规模逐渐减小.地表到深度10km左右,西、南华山隆起和鄂尔多斯西缘带呈高阻特性,西吉、兴仁堡-海原、中卫—清水河和中宁-红寺堡4个盆地的电阻率较低且呈盆地凹陷形状.其中兴仁堡-海原盆地电性基底最深,显示为南西深北东浅的“簸箕状”起伏形态.研究区发育不连续的壳内低阻带,与该区中、强震活动密切相关.1920年海原大震区存在明显的电性结构差异,震区南西侧和上部区域为相对高阻,北东侧和下部区域为相对低阻.