Physicochemical and thermophysical properties of CaO–TiO2–SiO2–Na3AlF6 system based electrode coating for AUSC power plant

The aim of this study is to investigate the physicochemical and thermophysical properties of CaO–TiO₂–SiO₂–Na₃AlF₆ based electrode coating developed for the welding of advanced ultra-supercritical (AUSC) thermal power plant components. The extreme vertices approach has been used to create twenty-six electrode coating compositions. Various physicochemical and thermophysical properties were characterized using experiments. The coating properties are essential in ensuring sound weld with desirable in-service performance. The developed coating's structural behavior was analyzed using Fourier transformation infrared spectroscopy (FTIR) and X-ray diffraction (XRD). In addition, regression analysis was carried out to evaluate the influence of coating constituents. Individual constituents and their interaction were found to have a prominent role in influencing the physicochemical and thermophysical properties.     

“Size effect” in the fatigue behavior of Friction Stir Welded plates

Comparative fatigue tests were carried out on Friction Stir Welded specimens of a 2195-T8 aluminum–lithium alloy that differed significantly in width. The width of the larger specimens was over thirteen times greater than that of the small specimens. Fatigue results showed a clear “size effect”, i.e. fatigue life of large specimens was about 40% of the corresponding value of small specimens. The Equivalent Initial Flaw Size methodology was adopted to correlate the two sets of results. Fatigue crack initiation life was disregarded with respect to crack propagation life, and fatigue life was evaluated only as propagation of a small pre-existing defect. Following this methodology, test results of small specimens were used to evaluate the initial equivalent flaw contained in each specimen. It was assumed that this data followed a normal distribution. The equivalent initial flaw in larger specimens was evaluated by simple geometrical considerations. A very good assessment of mean fatigue life and scatter in the fatigue results of large specimens was obtained by simulating the propagation of these defects. Calculations were carried out by taking also welding residual stresses into account, but the results demonstrated that this effect was not significant.     

Fatigue performance of Friction Stir Welded titanium structural joints

The Friction Stir Welding process for producing corner and T-joints out of 6 mm Ti–6Al–4V was developed in this effort using previous work on butt weld joints as a starting point. A limited number of corner joints were also subjected to a bending fatigue test to preliminarily assess the applicability of the process in producing fatigue critical structures. These results were also compared to predictions made by applying stress concentration factors to previously generated uniaxial butt joint test data. While additional testing is still required to obtain a higher degree of confidence in the conclusions of this study, it was found that the performance of these corner joints in fatigue could be compared to butt joint data when a geometrically based stress concentration factor is applied. Furthermore, these welded joints possessed equivalent fatigue performance relative to identical test specimens machined from wrought product forms, both bar and extrusion. Thus, from the perspective of fatigue design, this study has shown that Friction Stir Welding is able to produce structures with the same performance as currently made from wrought materials.     

The influence of the fabrication process on the buckling of thin-walled steel box sections

Steel box sections are usually fabricated from flat plates which are welded at the corners. The welding process can introduce residual stresses and geometric imperfections into the sections which can influence their strength. For some thin-walled sections, large periodic geometric imperfections have been observed in manufactured sections. Subsequent investigations have indicated that the imperfections are in fact buckling deformations i.e. the box section has buckled due to welding residual stresses prior to any application of external load. The welding procedure and the behaviour of the box sections under load has been modelled using a finite element analysis that accounts for both geometric and material non-linearities. Tests have been carried out on box sections with a range of width to thickness ratios for the plate elements. Modelling has been shown to give good correlation with the test results. The conditions for buckling to take place as a result of the welding process have been established. A design method has been proposed.     

街面水电站混凝土面板堆石坝主要技术问题探讨

街面水电站拦河坝为混凝土面板堆石坝,在面板止水结构型式、面板防裂措施、上游面的施工方法、趾板开挖处理及趾板灌浆等方面,根据工程实际情况,结合国内外的新技术新工艺进行了探讨。     

Gleeble 3800热模拟试验机在宝钢的典型应用与功能开发

热模拟试验可研究成分与各工艺参数对组织和性能的影响，用于指导产品设计和实际生产工艺的制定，还有助于建立数学模型。文章介绍了Gleeble 3800热／力模拟试验机在宝钢实际应用中的几个典型试验，包括高温热塑性试验、多道次变形试验、冷轧薄板相转变点试验和HAZ焊接热影响区热模拟试验等。这些试验可用来解决连铸、轧钢和冷轧产品热处理生产中存在的一些问题。     

焊接试样的焊缝外形尺寸对爆炸试验的影响

选用水面舰艇用９４５钢和潜艇用９２１Ａ钢，研究了不同焊缝外形尺寸对爆炸试验中三缺口试样的中央缺口开裂行为的影响。通过大量的试验数据，确定了开裂判据ｅ≤ｅ_ｍ，为试验前预示中央缺口开裂与否提供了可靠的依据。     

The influence of silicon on carbon redistribution in steel weldments

Carbon redistribution was measured in ST1/ST2 Fe-2.5Si-0.8C/Fe-0.32Si-0.49C steel weldments in the temperature range 500–1000 °C. At the temperatures where austenite exists, carbon diffuses from ST1 into ST2; when ferrite is present, the diffusion flow reverses from ST2 into ST1. This effect is attributed to the degree of the silicon influence on the graphite precipitation and carbon activity in ST1 and ST2 steels. The opposite signs of the activity gradients in austenite and ferrite cause the reversal of the carbon diffusion when the annealing temperature is changed from the austenite to the ferrite temperature region. The carbon diffusion coefficients D_C and the thermodynamic interaction coefficients ε_C^Si in austenite have been assessed from the experimental data for ST1 and ST2 steels.     

铝合金高速船船体建造工艺

简述了ＬＦ１５和ＬＦ１６两种新型船用耐蚀可焊铝合金及其配套焊接材料在实船建造中的应用情况。阐述了铝合金全焊结构船体建造的关键技术及我国铝船体建造的３种方法     

不清根手工双面焊材料及工艺研究

本文分析了中厚板传统手工双面焊存在的诸如打底焊焊缝质量无法保证，需用碳弧气刨清根；工人劳动强度大；生产效率低；焊接质量不稳定等主要问题。为提高打底焊焊道质量，不用清根使背面得到良好的凹成形，研制了适合Ｘ形坡口的梯形体陶瓷衬垫。探讨了焊缝背面成形的主要影响因素及控制方法。