材料期刊网

Formation and Thermal Stability of Large Precipitates and Oxides in Titanium and Niobium Microalloyed Steel

ZHUO Xiaojun , WOO Daehee , WANG Xinhua , LEE Haegeon

钢铁研究学报(英文版)

Ascast CC slabs of microalloyed steels are prone to surface and subsurface cracking. Precipitation phenomena initiated during solidification reduce ductility at high temperature. The unidirectional solidification unit is employed to simulate the solidification process during continuous casting. Precipitation behavior and thermal stability are systematically investigated. Samples of adding titanium and niobium to steels have been examined using field emission scanning electron microscope (FESEM), electron probe Xray microanalyzer (EPMA), and transmission electron microscope (TEM). It has been found that the addition of titanium and niobium to highstrength lowalloyed (HSLA) steel resulted in undesirable large precipitation in the steels, ie, precipitation of large precipitates with various morphologies. The composition of the large precipitates has been determined. The effect of cooling rate on (Ti,Nb)(C,N) precipitate formation is investigated. With increasing the cooling rate, titaniumrich (Ti,Nb)(C,N) precipitates are transformed to niobiumrich (Ti,Nb)(C,N) precipitates. The thermal stability of these large precipitates and oxides have been assessed by carrying out various heat treatments such as holding and quenching from temperature at 800 and 1 200 ℃. It has been found that titaniumrich (Ti,Nb)(C,N) precipitate is stable at about 1 200 ℃ and niobiumrich (Ti,Nb)(C,N) precipitate is stable at about 800 ℃. After reheating at 1 200 ℃ for 1 h, (Ca,Mn)S and TiN are precipitated from CaAl oxide. However, during reheating at 800 ℃ for 1 h, CaAlTi oxide in specimens was stable. The thermodynamic calculation of simulating the thermal process is employed. The calculation results are in good agreement with the experimental results.

关键词: carbonitride;microsegregation;dendritic region;unidirectional solidification;heat treatment;thermal stability

NonMetallic Inclusion Distribution in Surface Layer of IF Steel Slabs

ZHANG Qiaoying , WANG Litao , WANG Xinhua , LI Hong , WANG Wanjun

钢铁研究学报(英文版)

Nonmetallic inclusion distribution in the surface layer of IF steel slabs during unsteady casting was investigated using the original position statistic distribution analysis (OPA) method. It was found that most nonmetallic inclusions larger than 10 μm existed in the subsurface layers of 05-35 mm from the slab surfaces and very few large nonmetallic inclusions were found in the inner regions (≥45 mm from slab surfaces). In addition, it was found that at high casting speed level (14 m/min), even a slight change of casting speed could result in a remarkable increase of the nonmetallic inclusions. Thus, at high casting speed, changing the casting speed should be avoided or considerably lower speed changing rate must be used.

关键词: IF steel;transient casting;slab surface layer;nonmetallic inclusion

In Situ Observation of Solidification Process of AISI 304 Austenitic Stainless Steel

HUANG Fuxiang , WANG Xinhua , ZHANG Jiongming , JI Chenxi , FANG Yuan , YU Yan

钢铁研究学报(英文版)

The solidification process of AISI 304 stainless steel during cooling at a rate of 005 K/s has been observed in situ using a confocal scanning laser microscope (CSLM). The results show that the δ phase appeared first in liquid steel, as the temperature decreased, the γ phase precipitated prior at δgrain boundary at 1 4522 ℃, the liquid steel disappeared at 1 4313 ℃, and then the γ phase precipitated on the δ ferrite. Based on the ScheilGulliver solidification model, the solidification processes of AISI 304 stainless steel are simulated using the Scheil model in ThermoCalc, and the simulation results agree well with the results observed in the experiment.

关键词: stainless steel;confocal scanning laser microscope;strip casting;ThermoCalc

Water Modeling of Optimizing Tundish Flow Field

LIU Jingang , YAN Huicheng , LIU Liu , WANG Xinhua

钢铁研究学报(英文版)

In the water modeling experiments, three cases were considered, ie, a bare tundish, a tundish equipped with a turbulence inhibitor, and a rectangular tundish equipped with weirs (dams) and a turbulence inhibitor. Comparing the RTD curves, inclusion separation, and the result of the streamline experiment, it can be found that the tundish equipped with weirs (dams) and a turbulence inhibitor has a great effect on the flow field and the inclusion separation when compared with the sole use or no use of the turbulent inhibitor or weirs (dams). In addition, the enlargement of the distance between the weir and dam will result in a better effect when the tundish equipped with weirs (dam) and a turbulence inhibitor was used.

关键词: tundish;flow field;turbulence inhibitor;weir;dam;water modeling experiment

Two-step magnetization in a spin-chain system on the triangular lattice: Wang-Landau simulation

Physical Review B

The Wang-Landau algorithm is used to study the thermodynamic and magnetic properties of triangular spin-chain system based on two-dimensional Ising model in order to understand the magnetic-order dynamics in Ca(3)Co(2)O(6) compound. The calculated results demonstrate that the equilibrium state of the rigid spins produces the two-step magnetization curve at low temperature even when the random-exchange term is considered. This work indicates that the four-step magnetization behavior observed experimentally must be due to the nonequilibrium magnetization.

关键词: calcium compounds;exchange interactions (electron);Ising model;magnetisation;thermodynamics;one-dimensional ca3co2o6;density-of-states;compound ca3co2o6;phase-diagram;proteins;crystal

ACRT-B法生长的MnxCd1-xIn2Te4晶体的溶质分凝特性

常永勤 , 介万奇 , 郭喜平 , 陈福义 , 安卫军

功能材料

研究了ACRT-B法生长的Mn0.1Cd0.9In2Te4晶体中界面的形状和各组元沿轴向的分布规律及其分凝因数.发现结晶界面为椭球形;采用理想配比生长MnxCd1-xIn2Te4晶体,其4种组元并不按(Mn,Cd):In:Te=1:2:4比例结晶,而是要重新分布;通过数学方法处理实验数据得到Mn,Cd和In的分凝因数在α相区分别为1.286、1.9257和0.7294,在β相区则分别为1.12、1.055和0.985.

关键词: ACRT-B法 , MnxCd1-x In2Te4 , 界面 , 分凝因数

Bridgman法生长的Mn_xCd_1-xIn₂Te₄晶体相形成规律和物理性能研究

常永勤 , 安卫军 , 郭喜平 , 介万奇

无机材料学报

采用Bridgman法生长了x为0.1,0.22和0.4的四元稀磁半导体化合物Mn_xCd_1-xIn₂Te₄晶体.研究了三根晶体中相的形貌、结构、成分和Mn_0.1Cd_0.9In₂Te₄晶体中各组元沿轴向和径向的成分分布.晶体生长初始端的组织为α+β+β₁,随着生长的进行,形成β相的单相区.在晶锭末端,形成In₂Te₃类面心立方结构化合物.组分x增大后,Mn_xCd_1-xIn₂Te₄晶体的吸收边向短波方向移动,禁带宽度则线性增大.磁化率测量结果表明:晶体在高温区的x^-1-T曲线服从居里-外斯定律,在低温区(<50K)则表现出顺磁增强现象.

关键词: Mn_xCd_1-xIn₂T_e4 , compositional distribution , infrared transmission spectra , mag- netic susceptibility

Bridgman法生长的MnxCd1-xIn2Te4晶体相形成规律和物理性能研究

常永勤 , 安卫军 , 郭喜平 , 介万奇

无机材料学报 doi:10.3321/j.issn:1000-324X.2003.02.004

采用Bridgman法生长了x为0.1,0.22和0.4的四元稀磁半导体化合物MnxCd1-xIn2Te4晶体.研究了三根晶体中相的形貌、结构、成分和Mno.1Cd0.9In2Te4晶体中各组元沿轴向和径向的成分分布.晶体生长初始端的组织为α+β+β1,随着生长的进行,形成β相的单相区.在晶锭末端,形成In2Te3类面心立方结构化合物.组分x增大后,MnxCd1-xIn2Te4晶体的吸收边向短波方向移动,禁带宽度则线性增大.磁化率测量结果表明:晶体在高温区的x-1-T曲线服从居里一外斯定律,在低温区(＜50K)则表现出顺磁增强现象.

关键词: MnxCd1-xIn2Te4 , 成分偏析 , 红外透射光谱 , 磁化率

MnxCd1-xIn2 Te4晶体生长研究

常永勤 , 安卫军 , 郭喜平 , 介万奇

功能材料

采用Bridgman法生长四元稀磁化合物半导体Mn0.22Cd0.78In2Te4晶体.当晶体生长到预定长度时,淬火得到固液界面.采用光学显微镜、扫描电镜、X射线衍射仪、ISIS能谱仪以及Leica定量金相分析仪研究了晶体中出现的界面形态、相的形貌和数量以及沿生长方向的相析出规律,并进行了相成分分析.研究发现,淬火得到的Mn0.22 Cd0.78In2Te4晶体中存在两个界面,其中一个为固液相变界面,另一个为由α+β两相区发展到单相β区时的转变界面,二者相对于生长初始端均为凹形;α+β两相区中,β相以条状、花状和近似圆片状形式存在,其中条状β相多分布在晶界处;越接近生长初始端,花状和近似圆片状β相越小,条状β相越细,它们的含量越少;X射线衍射图谱表明,β相为黄铜矿结构,α相为面心立方结构.

关键词: MnxCd1-xIn2Te4 , 相变界面 , β相 , X射线衍射图谱

Composition Distribution in the MnxCd1-xIn2Te4 Ingot Grown by ACRT-B Method

材料科学技术（英文）

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