Applied Mechanics and Materials Vols. 556-562

Abstract: With ABAQUS software, a finite element model is built to simulate the temperature field of 150mm ultra thick plate for 12Cr2Mo1R pressure vessels during heat treatment. The simulation results show that the plate^’s temperature between the surface and the core is difference during cooling process. Temperature difference is gradually increased with cooling process, then the temperature distribution of plate in the thickness direction becomes uniform. When quenching temperature is 910 °C and cooling medium is water, the microstructure at plate^’s quarter in the thickness direction is bainite. Simulation results provide theoretical reference for determining heat treatment technology in industrial production of ultra thick plate.

Abstract: The heat treatment process, normalizing plus tempering, of 150 mm-thick plate of 12Cr2Mo1R pressure vessel steel was proposed according to the results of finite element simulation and static CCT curve obtained by thermal simulation experiments. After normalizing at 910 °C for 10 minutes followed by water cooling and tempering at 650 °C for 60 minutes, the microstructure at 1/4 position along the thickness direction of the thick plate consists of bainite and all the mechanical properties meet delivery requirements.

Abstract: The continuous cooling transformation (CCT) behavior of a Ti attached steel was studied through thermal simulation tests, and the influences of different cooling rates on the microstructure and transformation were investigated. The results show that the microstructure changes with the cooling rate, and the CCT curve of studied steel is plotted, which indicates that the solid-state phase transformation mainly consists of four regions. The CCT diagram made it possible to predict the microstructures of studied steel with different cooling rates.

Abstract: On the basis of orthogonal experiment, the effect of heat treatment on structure and mechanical properties of Al-30 wt.% Si alloys refined and modified with Sr+B+RE has been investigated. The results show that the solution temperature and holding time on the alloy microstructure and hardness are affected. When the holding time is constant, as the solution temperature increased, primary silicon more fully integrated into the matrix, the matrix divided by the effect of more and more obvious, eutectic structure becomes coarse, roundness becomes high, the alloy hardness to improve. When the solution temperature is constant, with the holding time increased, primary silicon more fully integrated into the matrix, the matrix divided by the effect of more and more obvious, eutectic structure becomes coarse, roundness becomes high, the alloy hardness increase. When the temperature reaches 540°C, the holding time makes eutectic roundness variation, the hardness declines, the alloy hardness is hardest when solution temperature is 540°C and the holding time is 7h. Optimum heat treatment parameters: 540°C×7h.

Abstract: Aiming at corrugated surface, scratches, BUE defects and wrong grinding size of blank sheet of high cobalt cemented carbide exists in the traditional grinding process, the reason for these problems are analyzed. Constant feed motion mode is provided for related reason, transmission design and pneumatic speed control loop design are processed; the point-contact online synchronization measurement system is researched and designed to achieve a real-time synchronous detection of the blank sheet grinding; the electric control system of tool is designed based on PLC, automation of tool is achieved. Production efficiency is increased effectively, the labor intensity of workers is improved.

Abstract: The present paper introduces a modification method of welded joint, plasma spurt spraying (MPSS), for improving the fatigue life of welding structure. Nickel-base alloy powder was used to spray the welded joint of Q235B steel. The high cycle fatigue tests of specimens treated by MPSS were carried out to obtain the S-N curves. Meanwhile, numerical simulation was performed to obtain the residual stress field after spraying. Test results show that the fatigue strength of welded joint by MPSS is higher than that of as-welded joint. Based on the test results and simulation results, it can be concluded that MPSS improves fatigue strength mainly through the decrease of stress concentration and residual stress.

Abstract: Metal cutting processing is the most fundamental, most widely and the most important processing in industrial production. Because the development of mechanical manufacturing level plays a very important role in the coating technology material machining process. A coated carbide cutting tool with its high hardness and high wear resistance, good chemical stability and extensive compatibility characteristics, is widely applied in the metal cutting processing field. The author mainly studies the cutting force contrast between coated carbide cutting tools and not coated ones. Cutting tests have testified that if PVD technology applied on cutting, the cutting force of hard alloy cutter will alter with the change of feeds (f), depth of cutting (ap) and cutting velocity (v). The experiment suggests that the size of three-way cutting force of either the brand ZP25 hard alloy cutter or the carbide cutter by employing matrix ZP25 hard alloy cutter to respectively using PVD technology coat TiN or TiCN coating is successively FZP25>FTiCN>FTiN. The main reason for this is that the difference of frictional factor of the three kinds of cutter material and the workpiece material.

Abstract: Dissolved gas analysis (DGA) in transformer oil is considered as one of the preferred projects to discover the potential faults of the transformer. To identify the aging characteristics of oil-immersed transformer oil in long-term operations, it is important to study relationship between total hydrocarbon and gases dissolved in transformer oil. This paper used Pearson correlation coefficient to analyze the relationship with the data of DGA. At last, it gives the result that the correlations between the total hydrocarbon and carbon monoxide, methane, ethane, ethylene, acetylene was positive. Therefore, this study lays the foundation which help to diagnose the aging status of transformer.

Abstract: Discussing the influence between the linear-weld-line TWBs’ different thickness of base metal and the formability of sheet by Dynaform FEM simulations technology and Dome test. Meanwhile, the correlation with the difference thickness of base metal and the limit doming height, weld-line movement are proposed, we find that both sides of the TWBs’ thickness have a great influence on the forming process. Then, the mathematical expressions are proposed between the changing thickness of base metal and limiting dome height, weld-line movement by using the genetic algorithm to fit the simulations’ data, which provide an evidence for production in theory.

Abstract: Cutting temperature always highly reaches over to 1000°C when high speed machining with PCBN tools. Diffusion of tool material element may have important influence on tool wear at such high temperature, the diffusion wear and oxidation wear have become the major wear mechanism. In this paper, the rules of diffusion wear and oxidation wear for PCBN cutting tools are proposed and analyzed based on thermodynamics theory. Dissolution concentrations in typical normal workpice materials of PCBN tool material at different temperature are then calculated. Diffusion reaction rules in high temperature are developed and analyzed using Gibbs free energy criterion. The machining tests were conducted using the PCBN tools at different cutting speeds of 50, 95,100 and 180 m/min, feed of 0.1, 0.2 and depth of cut of 0.1, 0.8, 1, and 1.5 mm respectively on PUMA300LM numerically-controlled lathe. It was found that the theoretical results were uniform with the experimental data; the results will provide useful references for tool material design and selection.