焊接残余应力对管线钢防腐性能的影响

借助有限元分析手段对X80管线钢对接接头的残余应力进行仿真计算,得到残余应力分布情况.采用X射线衍射法和盲孔法对预测结果进行试验验证.结果表明,周向残余应力总体变化趋势呈现先增大,稳弧后应力平稳达到峰值位置保持,在接近收弧位置,残余应力值减小;轴向残余应力总体变化趋势呈现先增大,残余应力达到峰值位置后平稳下降.残余应力仿真预测结果与两种测量方法所得结果相吻合,X射线衍射法结果高于盲孔法应力结果.通过有限元仿真技术预测应力较大位置,此技术对有效防止应力腐蚀开裂有一定的工程应用指导意义.     

堆焊金属残余应力场的计算机模拟

采用60CrMnMo钢为基体材料,用AST型X射线应力分析仪对堆焊残余应力场进行了测定。发现在堆焊金属中心部位和熔合区附近的热影响区出现了两个残余拉应力峰值。用ANSYS计算软件,模拟了堆焊过程中温度场和残余应力场的分布,在模拟中考虑了马氏体相变、杨氏模量与其它参数对计算结果的影响,并将计算值与残余应力场的测量值进行了比较。结果表明,残余应力场的计算结果与实测结果吻合较好,说明本文建立的有限元计算模型是有效的。采用这一模型,模拟了不同试样尺寸对堆焊金属残余应力场分布的影响。计算结果表明,随着试样尺寸的增大,残余应力峰值增大,且峰值益发生变化。     

2B25-T351压印强化残余应力场的有限元模拟与实验

运用有限元软件ABAQUS建立压印强化残余应力场的三维有限元模型,模拟计算压印强化过程中2B25-T351铝合金构件的三维残余应力场分布,模拟结果表明,压印痕底部残余应力沿厚度方向呈梯度分布,与表面距离越远,压应力水平越小。孔周围的残余应力分布比较集中,压印痕端头附近,孔边为相对均匀的残余压应力,其他位置为自平衡的残余拉应力;使用X射线衍射应力分析技术测量实际试样的残余应力,结果表明,实验测量值与有限元模拟值吻合较好;对压印强化前后试样进行疲劳性能试验,结果表明,压印强化在试件表面引入残余压应力,可降低裂纹萌生的几率及裂纹扩展的速率,压印强化后材料的疲劳寿命提高了近1.5倍。     

3003铝合金X射线法表面残余应力的检测

采用X射线衍射法测量铝合金3003基体材料表面残余应力中用到的衍射角.试验中,将等强度梁加载后表面产生的应力假设为“表面残余应力”,用传统电测法和X射线法分别测量加载后铝合金3003等强度梁的应力值.以电测值为参照,考察X射线法在衍射角为142°和156°时的应力测量值,并对其进行对比分析.试验表明,衍射角为142°时的测量结果存在非测量不当引起的测量非线性点.因此,X射线测铝合金3003宏观表面残余应力的最佳衍射角为156°.     

薄壁Ti6Al4V管件采用不同车削参数加工引起的表面残余应力的测量

切削加工引起的金属零件的表面残余应力,其性质和大小对零件的服役性能产生很重要的影响。在测量车削加工Ti6Al4V薄壁管件引起的表面残余过程中,由于边缘效应的存在,使得零件的长度对测量精度有严重的影响。由于管件的壁厚很薄,当去除一应力层时会对剩余部分的残余应力的重新分布产生重要的影响,因此必须对剥层后X射线法测得的应力值进行修正补偿才能得到其初始应力值。传统的修正方法其计算比较复杂,对零件和应力都有特别的要求,而且在某些情况下其修正精度还达不到要求。同时考虑测量精度、测量可行性以及节约材料诸多方面的问题,本文运用有限元验证的方法确定零件合适的长度。同时本文运用精度较高的基于有限元分析的修正方法结合X射线法测量Ti6Al4V管件车削加工引起的表面残余应力,分析不同切削参数以及退火处理对表面残余应力的影响。结果显示：切削速度、进给量以及切削深度在指定范围内增大时会导致表面切削和进给方向的压应力增大,退火处理会使得表面两个方向的残余应力减小将近85%。     

残余应力及其分布的X射线二维衍射分析与计算

根据在X射线二维衍射几何关系下建立的应力应变基本方程，提出了一种基于X射线多晶面探测器衍射系统的残余应力及其分布测量方法，即通过分析X射线衍射圆锥的变形程度确定应变张量，进而计算应力张量。该方法有效地利用X射线面探测器的“虚拟摆动”功能，在一定程度上解决了传统X射线衍射法较难处理的粗晶材料和有织构材料的残余应力测量问题。对304不锈钢的残余应力及其分布进行了分析与计算，结果表明，该合金呈表面残余压应力，并且应力分布比较均匀。     

金刚石薄膜残余应力的X射线透射测量法

用X射线衍射透射法测量了不同沉积工艺CVD自支撑金刚石薄膜的残余应力，并对应力测试结果进行初步分析。与常规法相比，透射法直接测量薄膜表面不同方向的正应变，计算出正应力值，不需要复杂的转换计算，测量过程简捷、准确，克服了常规法的不足，有利于推动薄膜残余应力的研究。     

基于快速面探测方法的碳化硅表面残余应力测量

陶瓷加工后表面残余应力的测量通常采用一维X射线衍射线探测法,该方法存在测量过程烦琐、效率低、成本高等问题,因此采用新型快速二维面探测X射线衍射残余应力测量方法,对碳化硅陶瓷表面的残余应力进行测量,实验中测量了3种不同品牌碳化硅工件的初始表面和抛光后表面的残余应力。结果表明:此新方法单次测量即可获得样品500点的衍射信息,特别适用于陶瓷材料的应力测量。同时还发现:对于被加工表面的残余压应力,抛光加工最高能够消除近80%的残余应力,但不能改变工件的残余应力分布。      

数值模拟和实验研究Ti6Al4V合金激光熔透焊接残余应力

采用热-弹塑性三维有限元法研究激光熔透焊接Ti6Al4V合金的残余应力,并采用小孔法测量焊接残余应力以和计算结果进行比较.有限元计算时,建立了以焊缝形貌尺寸为参数的统一锥形热源模型来模拟不同热输入时的焊接温度场,并讨论了边界条件和有限元网格大小的确定.研究结果表明:采用焊缝轮廓尺寸作为热源参数能准确模拟焊缝横截面轮廓;钛合金激光熔透焊接的纵向残余应力分布梯度陡;在焊件表面和内部残余应力分布趋势不同,采用小孔法测量的残余应力分布和计算的焊接件内部残余应力分布相似.     

基于轮廓法测试惯性摩擦焊接头内部残余应力

采用轮廓法测试小尺寸镍基高温合金惯性摩擦焊接头的内部环向应力、中等尺寸惯性摩擦焊接头内部环向和轴向应力;分析惯性摩擦焊接头内部环向和轴向残余应力分布特征.结果表明,轮廓法能测试小尺寸及窄小焊缝试件的内部残余应力,能反映出窄小焊缝内部的大梯度焊接残余应力全貌;惯性摩擦焊接头的环向应力沿轴向变化剧烈,沿环向分布均匀,沿厚度分布不均匀;焊缝中心位置外表层区域环向应力小于内表层区域环向应力;焊缝中心外表面轴向应力为压应力,而内表面轴向应力为拉应力,且轴向应力沿厚度呈线性变化.     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

LASER CLADDED TiCN COATINGS ON THE SURFACE OF TITANIUM

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

GROWTH MORPHOLOGIES OF A BINARY ALLOY WITH LOW ANISOTROPY IN DIRECTIONAL SOLIDIFICATION

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.     

STUDY ON PROPERTIES OF PULSE ELECTRODEPOSITED RE-Ni-W-P-SiC COMPOSITE COATINGS

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.     

RELATIONSHIP BETWEEN J-INTEGRAL AND FRACTURE SURFACE AVERAGE PROFILE

To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed The principle of the fracture-surface topography analysis （FRASTA） was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.