Effect of microstructure on the impact toughness of a bainitic steel bloom for large plastic molds

The correlation between the impact toughness and microstructural characteristics of a large bainitic steel bloom has been investigated. The study focuses on microcrack nucleation and propagation in the basic cleavage plane. To analyze the phase transformation during the wind-cooling process, the temperature field of the bloom was acquired by computer simulation, and a continuous cooling transformation experiment was conducted. The results show that compared with the surface of the bloom, the toughness of the bloom’s core is decreased by the increase in proeutectoid ferrite and the coarsening of tempered martensite–austenite constituents. The proeutectoid ferrite decreases the toughness via its effects on carbide precipitation, the formation of martensite–austenite constituents, and the bainite transformation. The relatively large tempered martensite–austenite constituents are conducive to microcrack nucleation and propagation.     

Effect of alloying elements and processing parameters on the Portevin-Le Chatelier effect of Al-Mg alloys

The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of Al-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testing was performed in various Zn and Mg contents under different annealing and cold-rolling conditions. In the results, the stress drop and reloading time of serrations increase with increasing plastic strain and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg or Zn content. The alloys with a greater intensity of serrated yielding generally exhibit a greater elongation. The stress drop and reloading time of serrations decrease with increasing grain size in the case of the annealed samples. The cold-rolled sample exhibits the most severe serration because it initially contains a large number of grain boundaries and dislocations.     

Effect of Continuous Cooling Conditions on Microstructure and Mechanical Properties of High Carbon Steel Rod

The effect of cooling rate and austenitizing condition on the mechanical properties of high carbon steel (SWRH82B) has been investigated. Specimens were made of high carbon steel rod and heat-treated by Gleeble-2000 to produce a wide variation in prior austenite size. Different cooling rates were carried out, and then pearlite interlaminar spacing and mechanical properties were measured and tested respectively. According to the results, it could be found that under the continuous cooling with the increase of cooling rate, tensile strength greatly increases and reduction in area exhibits a slightly increase for an equivalent value of prior austenite grain size. When prior austenite size increases, reduction in area decreases, and tensile strength increases slightly for an equivalent value of pearlite interlaminar spacing. It is concluded that prior austenite size primarily controls ductility and pearlite interlaminar spacing controls tensile strength. Mathematical formulae are given for these relations.     

PREPARATION OF COMPLEX ZrO2-Y2O3 SOL

Complex ZrO₂-Y₂O₃ sol were prepared from precursors of inorganic salts and metal alkoxides. The processes for complex ZrO₂-Y₂O₃ sol preparation and purification, the sol-gel transformation and the characterization of the sol from the two kinds of precursors were discussed and compared. It was found that the colloidal particles were amorphous in nature, and extremely fine (<10nm) in the both cases. ZrO₂-Y₂O₃ coatings on GH220 superalloy samples MCrAlX (M=Fe, Co, Ni, X=Y, Ta,Hf…) pre-coated) were prepared using sols from the two different processes and tested at 1000 ℃ for 100 h in laboratory air. Results showed that only the coatings from the metal alkoxides derived sol offered excellent oxidation resistance.     

Mssbauer谱技术对古陶瓷烧制气氛的研究

Mssbauer效应是由西德科学家R.L.Mssbauer在1958年所发现的一种γ射线的共振荧光现象,也称之为γ射线无反冲发射及共振吸收效应。由于它对γ射线能量的细微变化十分敏感,可利用这种效应来探测由于共振原子核附近的物理和化学环境变化而引起的共振γ射线能量的细微改变.用~(57)FeMssbauer谱技术可以在取样少量(几十到几百mg)的情况下,对古代陶瓷的表层和内层进行分析研究.根据其Mssbauer谱中得到的特征超精细相互     

Hg^2＋对蚕豆根尖细胞的微核效应

目的 以蚕豆根尖为供试材料,以不同浓度的Hg2 为受检物质,探讨Hg2 对蚕豆根尖细胞的微核效应.方法 实验分析与统计分析.结果 Hg2 能诱发较高的微核率,在一定浓度范围内.其微核率随Hg2 处理浓度的升高而增加,但高于一定浓度后,微核率不再上升,反而有下降的趋势.结论 运用微核技术可以检测重金属环境污染物.     

The U/Ω effect of electricity parameters of the lotus root silk in the liquor with different pH values

The silk of lotus root is a kind of natural biomaterial with the advantages of easy absorbing and dis-solving and poisonless. It may become a new engineering material for clinic and tissue engineering. However, the relationship between its electricity parameters and the pH values of the liquor that the silk is dipped in is unknown presently. The electricity parameters of inductance, capacitance and imped-ance of the silk were measured in the environment with the temperature ranging from 23℃ to 25℃ and the humidity ranging from 45% to 55% when it was dipped in the liquor with different pH values for 24 h. The results show that the inductance and impedance vary in U shape curves with the liquor pH value, and the capacitance varies in Ω shape curve. The minimal value of the U curves and the maximal value of the Ω curve appear at the point where the pH value equals to 7. The phenomena are called the U/Ω effect. It means that the silk has perfect biocompatibility with human tissues. The study results may imply that the silk have broader potential applications in biomedicine, tissue engineering and bioelec-tronics. silk of lotus root, biomedicine engineering material, U/Ω effect, pH value of liquor     

二维热粘弹性问题中的辛方法

在辛体系下描述了二维热粘弹性力学问题.利用辛正交归一关系和积分变换得到了对偶方程的解,即圣维南解和局部解,从而将原问题转化为寻找零本征值本征解和非零本征值本征解问题.同时给出了一种辛空间中处理端部条件问题的有效方法.根据该方法,在数值算例中讨论了端部的局部效应问题。这种辛方法和数值算法为解决其他问题提供了一种可行的思路.