Materials Science Forum Vols. 704-705

Abstract: The distribution of residual stress in hot rolled large size H-beams is complex due to the uneven temperature distribution on the final rolling cross-sections. In this paper, 3D simulation analysis is conducted on the residual stress field of cooled large H-beams and the transformation of residual stress field during the flange cutting based on the calculations of thermo-mechanical coupling whole rolling process. There are tensile stress in the flange and web connection areas and compressive stress in web. During the flange cutting process, tensile stress increases suddenly when the kerf arrives at the flange and web connection area, resulting in the brittle fracture of the web. The method of controlling the residual stress of large H-beams is also simulated. Improvement in the distribution of residual stress is achieved through the forced cooling of the outside flange or reduction of the temperature differences on the final rolling cross-sections.

Abstract: The subject of the paper is a study of the material behaviour during hot rolling. The process considered is a rolling of round bar in roughing mill group which consist of four passes. The computer simulation of the process shows that the local plastic deformations which appear in the material are extremely large. This fact can leads to extension of surface defects. The dependences of maximum local plastic deformation on geometrical parameters of the calibres have been obtained and analysed during this study. The investigations performed, led to the development of new roll pass design which almost halved the maximum value of local plastic deformation in the material during the rolling. Since full 3D FEM models needs significant amount of computer memory and CPU time, it was not suitable for the performed study which involves a bulk of simulations with different initial conditions. Therefore, the quick algorithms for simulation of rolling processes which based on so-called “2.5D” method have been used. This method, due to number of simplifications, is significant faster then conventional 3D FEM, and at the same time it allows to reach good accuracy of the model. The developed computer software SPLEN(Rolling) which implements “2.5D” FEM simulations was applied for computations and analysis of the results. This software is able to predict the shape evolution of rolled material, as well as distributions of strain, strain rate and temperature within the volume of deformation zone. It has been shown that computer simulation based on “2.5D” FEM with SPLEN(Rolling) software can by efficiently used for optimization of technological procedures in rolling industry.

Abstract: There exists a large amount of longitudinal tensile stress in the weld bead of the TC4 thin plate for the uneven heating of the welding thermal resource. Owing to the equilibrium of the internal stress, longitudinal compressive stress is also large on the edge of the thin plate. When the compressive stress is larger than the critical buckling stress, the buckling distortion can take place. Therefore, the value of the critical buckling stress is important to judge the distortion. Some theoretical formula and empirical equation can not give the suitable solution to the judge of the critical value of the certain TC4 thin plate weldment because of the difficulty in the analytic solution and difference in the feature of the material and boundary condition. Finite element method was utilized to estimate the value of the buckling stress in the thin plate. Based on the solution, the adjustment of welding longitudinal compressive stress model is done. Henceforth, the critical buckling stress can be determined by the method. Keywords: critical buckling stress, TC4 thin plate, welding longitudinal residual stress

Abstract: A motion detection pointing device based on CMOS image sensor is presented in this paper. Mismatch of active pixel sensor and correlated double sampling circuit is analyzed by Monte Carlo method using H-SPICE. With a 3.3V supply voltage, the maximal offset voltage caused by all mismatch is 3.6043mV, less than 8-bit least significant bit. Therefore, the motion detection pointing device system could achieve 8bit precision. The contribution of each mismatch to the total maximal offset voltage is also analyzed, comparison shows photo diode current mismatch and saturation drain current mismatch are the main causes of offset voltage. Keywords: mismatch; offset voltage; Monte Carlo method

Abstract: The present study had investigated the joining performance of SiC particle reinforced aluminum metal matrix composite (Al/SiCp-MMC) having 1.0mm thickness by resistance spot welding processes. The welded joints were subjected to tensile-shearing tests in order to determine the strength of the welded zone. In addition both scanning electron microscopy (SEM) and optical microscopy (OM) were conducted to investigate the micro structural and micro hardness’s changes of the welded joints. The results reveal that: the maximum tensile-shear strength value of welded joint was obtained in these optimum welding parameters as in 17.5kA welding current for 60 periods welding. The electrode pressure was 3.5kN. It was favorable to select relatively high welding current and short welding time for improving mechanical properties of spot welded SiCp/LY12 composite joint. In this base, the welding mechanism of resistance spot welding SiCp/LY12 composite has also been discussed in detail.

Abstract: Annealing and dip galvanizing treatments of Galvalume were studied by using methods of Gleeble thermal simulation experiment and optical microscopy (OM), scanning electronic microscopy (SEM), X-ray energy dispersive analysis (EDAX), X-ray diffraction (XRD) and so on. Meanwhile, surface morphology, microstructure, phases and the respective compositions of Al-Zn alloy coating plate were analyzed. The results show that decreased rate and prolonged time of annealing treatment cause less effect on process ability of product, which all because of the short time of annealing process in continuous aluminum-zinc treatment. However, coarse grain which causes low strength, high elongation and r value occurs when rising annealing temperature. To get better coated surface, in-zinc pot temperature should be controlled in the range of 590~610°C, and height of air-knife nozzle should be kept in the range of 150~200mm. Surface layer of 55％Al-Zn alloy coating is covered by Al-Zn alloy, the intermediate alloy layer is consisted of binary and ternary compounds, such as θ phase (FeAl₃), Al_0.3Fe₃Si_0.7 and Al_3.21Si_0.47. Keywords: Galvalume, Process, Microstructure, Properties

Abstract: Based on Cahn-Hilliard nonlinear diffusion equation, the phase field model has been established for ternary alloy spinodal decomposition, which directly couples with Calphad thermodynamics and dynamics calculation and takes into account the effect of the coherent elastic energy. The simulated microstructures of spinodal decomposition were carried out in the isothermally-aged of Cu-6at.%Ni-3at.%Si alloy. The results indicate that the spinodal decomposition takes place at the early stage of Cu-6at.%Ni-3at.%Si alloy aging at temperatures of 723K, forming two-phases mixture of Cu-rich and Ni/Si-rich, and the decomposition microstructures are distributed in a semi-interconnected labyrinth-like form. Under the effect of the coherent elastic energy, the decomposition microstructures demonstrate the obvious anisotropic characteristics, and present interconnected rectangular stripes aligned along [10] and [01] directions. The growth of the decomposition microstructures is in accordance with the growth law of growth exponent n≈0.29, slightly less than the LSW’s prediction.

Abstract: The finite element method and physical simulation were used to research the section effect of 50mm heavy plate microalloyed with VN during rolling and the effect of controlled rolling schedule on the section inhomogeneity. We can conclude from the results that when the whole reduction of the plate is constant, the increase of reduction in pass makes for the deformation conveying towards center layer of plate and reducing the section inhomogeneity. To the process that 220mm thick plate blank was rolled to 50mm thick plate, when the rolling pass decreased from 10 to 6, the accumulated deformation of the center layer was increased from 58.35% to 67.87%, and the austenite grain size decreased from 41.3μm to 35.4μm. The effect of final rolling temperature depends on the heat preservation: if there is no heat preservation there almost has no effect on the section homogeneity; if there has a suitable heat preservation, the section inhomogeneity can be reduced efficiently, and the best homogeneity can be obtained when final rolled at 870°C. Key words: heavy plate, VN microalloying, section effect, finite element method

Abstract: By means of wear analysis of the wear-resistant steel used in the process, and adjust the wear-resistant steel composition, by adding alloying elements Cr, Mo and so on, optinlizing heat treatment technique, to get new wear-resistant steel. The HR-150A rock well hardness tester and JB-300B impact tester as well as SHIMADZUAG-I250KV on electronic tensile testing machine were used to test the mechanical properties of materials. In the test of friction and wear performance was done using the high temperature and high-speed friction of wear-testing maching (MMS-1G), and analysis of microscopy and the wear morphology by JSM-5610LV SEM．The results showed that: The hardness of new wear-resistant steel reaches HRC53, the impact toughness 23J/cm², And at this moment, the sample matrix is the microstructure of small lath martensite and residual austenite.

Abstract: Based on analyzing the stress-strain characters of material in nosing deformation zone, and considering two influencing factors, i.e. material thickness variation and material work-hardening, according to ignoring and considering the influence of additional bending stress at the entrance of die, and the different forms of work-hardening of metal materials, a new set of mathematical models of deformation force calculated for tube nosing with conical die are set up by utilizing slab method that belongs to one of the theoretic methods solving the problems of metal plastic forming. Furthermore, the scope of the application of every mathematical model of deformation force calculated for tube nosing with conical die is classified from conical die semi-angle and work-hardening of metal material point of view in theory.