Effects of welding wire composition and welding process on the weld metal toughness of submerged arc welded pipeline steel

The effects of alloying elements in welding wires and submerged arc welding process on the microstructures and low-temperature impact toughness of weld metals have been investigated.The results indicate that the optimal contents of alloying elements in welding wires can improve the low-temperature impact toughness of weld metals because the proentectoid ferrite and bainite formations can be suppressed,and the fraction of acicular ferrite increases.However,the contents of alloying elements need to vary along with the welding heat input.With the increase in welding heat input,the contents of alloying elements in welding wires need to be increased accordingly.The microstructures mainly consisting of acicular ferrite can be obtained in weld metals after four-wire submerged arc welding using the wires with a low carbon content and appropriate contents of Mn,Mo,Ti-B,Cu,Ni,and RE,resulting in the high low-temperature impact toughness of weld metals.     

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.     

Numerical simulation on the rheo-diecasting of the semi-solid A356 aluminum alloy

The effect of injection pressure, piston velocity, and the forming temperature of semisolid slurry on the filling behavior of the semi-solid A356 aluminum alloy was investigated by simulation methods. The simulation results show that these processing parameters have an important effect on the filling behavior of the semi-solid A356 aluminum alloy. The slurry flows steadily in the cavity when the injection pressure, the piston velocity, and the forming temperature are low, but it is prone to turbulent flow w...     

Comprehensive assessment on dynamic roof instability under fractured rock mass conditions in the excavation disturbed zone

The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine,China.The rock mass was particularly weak and fractured.There occurred 6 large-scale dynamical roof falls in the excavation disturbed zone (EDZ) with the collapsing volume of 216 m3.First,the field detailed geological environment,regional seismic dy-namics,and dynamic instability of roadways were generally investigated.Second,the field multiple-index monitoring measurements for detecting the deep delamination of the roof,convergence deformation,bolt-cable load,acoustic emission (AE) characteristic pa-rameters,total AE events,AE energy-releasing rate,rock mass fracture,and damage were arranged.Finally,according to the time-space-strength relations,a quantitative assessment of the influence of rock-mass damage on the dynamic roof instability was accomplished.     

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...     

Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization

A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060,10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

2014年4月网络安全监测数据发布

1木马僵尸监测数据分析 1.1中国境内木马或僵尸程序受控主机分析 2014年4月,中国境内（以下简称境内）211万余个I P地址对应的主机被木马或僵尸程序控制,与上月的199万余个相比增长6.2%。2013年5月至2014年4月,境内被木马或僵尸程序控制的主机IP数量月度统计如图1所示。     

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。     

耐久性弱化边坡模型试验及 ＤＩＣ位移测试研究

边坡岩土与支护结构长期耐久性能弱化对边坡变形及安全稳定性产生影响,开展定量化研究以指导边坡耐久性设计和评估分析具有重要意义。以锚喷支护边坡为例,通过几何相似比为 1∶50的模型试验探讨不同弱化程度的边坡受耐久性因素影响的效果。首先基于正交设计试验确定模型边坡岩层以及喷射混凝土层相似材料配合比,进一步设计单槽尺寸 0．75ｍ×1．5ｍ×1．1ｍ的双模型槽对比试验系统,模拟正常工况,以及降雨（7ｄ）＋风干（7ｄ）、酸雨／盐雾（7ｄ）＋风干（7ｄ）等边坡耐久性影响工况,基于 ＤＩＣ仪器测试不同工况条件下坡顶分次堆载对坡面位移变化影响。研究表明:支护结构材料耐久性能退化对边坡变形位移产生一定量影响,可为长期复杂环境影响下的边坡耐久性稳定性设计评估提供参照。     

碎石桩红黏土复合地基承载力与变形特性分析

在天然红黏土地基上进行高填方机场建设,其沉降与稳定性难以满足机场控制标准。碎石桩复合地基具有加速地基固结沉降和提高地基承载力的作用,可较好应用在红黏土地基处理中,但其作用机理不明确。基于西南某高填方机场的红黏土地基,通过室内试验和原位测试,研究碎石桩处理前后红黏土的物理力学特性,得出置换率为 7．0％时,碎石桩复合地基以排水固结为主要加固机理,处理 28ｄ未加载条件下地基承载力提高了 23．7％;利用 ＡＢＡＱＵＳ有限元软件对红黏土未处理地基和碎石桩复合地基在填筑荷载下的变形特性和孔隙水压力消散情况进行数值模拟,得出天然红黏土地基固结速率非常缓慢,工后沉降不能满足运行期道面运行要求,采用碎石桩处理后,红黏土软弱地基的排水固结速率得到大大提高,施工期固结度可完成 96．0％。研究结果得到了现场监测资料的验证,可为类似工程提供参考。