Effect of cooling temperature on the microstructure and corrosion behavior of X80 pipeline steel

Dual-phase accelerated cooling(DPAC) was applied to X80 pipeline steel to obtain its microstructure with different amounts of bainite and ferrite. The microstructure, hardness, and polarization behaviors of the steel, cooled to different temperatures, were investigated. Results showed that, with decreasing cooling temperature, the amount of polygon ferrite(PF) increased while that of acicular ferrite(AF) decreased. The amount of bainite correspondingly decreased, except when cooled to 760°C. Moreover, the grain size of ferrite increased. The corrosion behaviors of different phases were distinct. Martensite/austenite(M/A) islands presented at the grain boundary of the PF phase caused small pits. Numerous micro-corrosion cells were formed in the AF and bainite phases, where micropores were prone to form. X80 pipeline steel cooled to 700°C had the best corrosion resistance in the simulated seawater. The decreased amount of the PF phase reduced the area of cathode, resulting in slight corrosion. About 40 vol% of the bainite phase provided strength while the PF phase provided adequate ductility to the X80 steel. It was concluded that the appropriate cooling temperature was 700°C for ideal corrosion resistance and mechanical properties.

Research on deformation characteristics of JCOE forming in large diameter welding pipe

In the present work, the JCOE forming is inves- tigated using the finite element （FE） method. A two- dimensional FE model is established for the plane strain condition by FE code ABAQUS, and the FE model is vali- dated by experiments. The aim of this research is to inves- tigate forming quality states in the JCOE forming process; in particular, the effects of technological parameters on form- ing quality are evaluated. Taking the JCOE forming process of X80 steel φ1 219 mm × 22 mm × 12 000 mmwelding pipe for instance, the deformation characteristics of JCOE forming are analyzed, in which the geometry of the formed pipe, residual stress distributions and effects of process parameters on JCOE forming quality can be obtained. Thus, the presented results of this research provide an effective approach to improve welding pipe forming quality.

3D打印仿碳纳米管加筋混凝土单轴受压力学性能研究（英文）

目的:研究3D打印仿碳纳米管加筋结构对混凝土单轴受压力学性能的加固机制。创新点:提出一种采用仿碳纳米管加筋结构对混凝土进行加固的方法。方法:1.以韧性树脂为材料,采用光固化3D打印技术分别制作疏密度为每层10个单元、12个单元和14个单元的仿碳纳米管加筋结构和传统纵横加筋结构。2.将配制的M2.5水泥砂浆作为填充材料,制备直径为100 mm、高为200 mm的圆柱型单轴压缩试件。3.以相同尺寸内部无加筋的素混凝土试件作为参考进行抗压试验。结论:1.与素混凝土相比,当试件采用每层10个单元、12个单元和14个单元的仿碳纳米管加筋结构时,混凝土试件抗压强度分别提高59.77%、85.94%和108.98%。2.当试件采用每层10个单元、12个单元和14个单元的传统纵横加筋结构时,混凝土试件抗压强度分别提高24.22%、46.88%和68.75%。3.仿碳纳米管加筋结构对混凝土的加固效果明显优于传统纵横加筋结构。4.仿碳纳米管加筋后试件的破坏形式随着加筋密度的增加由整体破坏转变为局部破坏。