材料期刊网

Observations on the Formation of Ultrafine Ferrite Grain Size in Steels by Physical Simulation Routes

L.X.Pan , L.P.Karjalainen , M.C.Somani

材料科学技术（英文）

Some observations are reported on the simulation of two thermomechanical routes to produce ultrafine ferrite grain size in steels. One C-Mn grade and Nb, Nb-Ti and Nb-high Ti bearing steels were used in the tests performed on a Gleeble simulator and a laboratory rolling mill. The routes included severe hot deformation of prior grain-refined austenite at the temperature close to Ar3 (DIF) and static recrystallization of fine-grained cold-rolled martensite (SRM). It was observed that the hot deformation induces the formation of ferrite above the Ar3 temperature of the steel, but severe reductions are required for the complete transformation. Strain of 1.2 can result in about 70% of ferrite with the grain size of about 1.4～2 μm in all the studied steels. Similarly, in short annealing of cold-worked martensite, the static recrystallization can also lead to a grain size of about 1.5 μm. The distribution of carbon varies in the microstructures, carbon being in the second phase in the DIF route and in carbide particles in the SRM route, which may have a significant influence on the mechanical properties and the thermal stability of ultrafine grain structure.

关键词: Ultrafine grain size , null , null , null

Relationship between degeneration of M7C3 and precipitation of M23C6 in a cobalt base superalloy

Materials Science and Technology

The relationship between degeneration of the primary M7C3 carbide and precipitation of the secondary M23C6 carbide has been investigated in a cobalt base superalloy after 100 h aging at 850 degrees C. The results indicated that the primary M7C3 carbide could not transform in situ into the secondary M23C6 carbide. The M23C6 formed by a direct reaction between chromium and carbon atoms. The dissolution of M7C3 provided the precipitation of M23C6 with essential carbon, which acted as a carbon reservoir. Near M7C3, the chromium content is a controlling factor of M23C6 precipitation while away from it, the carbon content dominated the reaction. The precipitate free zone around M7C3 is attributed to chromium depletion which is inherited from the as cast condition. MST/4174

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ON THE M_7C_3 IN Cr27 CAST IRON

LI Yuqing WANG Cirong GU Zhaofeng Research Institute of Daye Steel Works , Huangshi , China Senior Engineer , Research Institute of Daye Steel Works , Huangshi 435001 , China

金属学报(英文版)

Determination of(Fe,Cr)_7C_3 in Cr27 cast iron results about 30 v.-%.Minor Si and Mn are present.Sectional area of the M_7C_3 grains is 1—50μm~2.Combining matrix analysis of elec- tron diffraction pattern with calculated angle between plane traces,{011}twins and also {013}twins producing local environment for Ru_7B_3 are observed in the orthorhombic M_7C_3. A crystallographic model for M_7C_3 is proposed.

关键词: cast iron , null , null , null , null

Zn-5%Al合金超塑性的m-C-δ(或m-k-δ)关系

刘勤 , 夏锄 , 刘晓东

金属学报

在170,190,210,230,250℃的温度下,采用3.7×10~2,7.4×10~2和1.1×10~(-1)min(-1)的应变速率(平均)对Zn-5%Al共晶合金的m-C-δ(或m-k-δ)关系曲线(简称m-δ关系曲线)进行了测定.所有的曲线均随应变的δ增加而快速上升.俟达到某一定的应变量(极限应变量δ1)后。开始缓慢下降并保持平稳直至断裂.Zn-5%A1共晶合金的m-δ关系曲线不存在k_(?)=k_I(k_(I 1),k_(I 2),k_(I 3),……)=k_F(或C_0=C_I(C_(I 1),C_(I 2),C_(I 3),……)=C_F=1)的简单情况.可应用m-δ方程式[4,5]对曲线上各点C值(包括所有的C_I和C_F值)进行计算.C值随δ值的增加成近似的直线上升.直线的斜率在极限应变(δ1)处突然减小.

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C60、M@C60(M=Si,Ge)富勒烯分子的压缩力学特性

沈海军

功能材料

采用基于Tersoff势的分子动力学方法,模拟了温度T=300、700和1100K下C60、M@C60(M=Si,Ge)富勒烯分子的对径压缩过程.根据模拟结果,讨论了温度T对3种富勒烯分子压缩力学特性的影响以及它们压缩力学特性的差异.研究表明,在300～1100K范围内,温度T对C60、M@C60(M=Si,Ge)分子压缩力学特性无显著影响;当压缩应变至8%～16%左右,各富勒烯分子在加载点处开始"塌陷",当压缩应变至28%～32%左右,各富勒烯达到承载极限;C60、Si@C60、Ge@C60分子依次具有由低到高的承载能力.

关键词: 富勒烯 , 分子动力学 , 力学特性 , 内嵌M@C60富勒烯

Coarsening of M23C6 Precipitates in an Fe-Cr-C Ternary Alloy

ZHU Na-qiong , LU Li , HE Yan-lin , LI Lin , LU Xiao-gang

钢铁研究学报(英文版)

Coarsening of M23C6 precipitates in an Fe-12.4Cr-0.13C ternary alloy has been investigated ageing at 780 ℃ up to 200 h. Evolution of M23C6 carbides at different ageing times was determined experimentally using transmission electron microscopy. Particle size distribution was obtained with different measuring methods. Simulations of coarsening of M23C6 precipitates were carried out using computational thermodynamics and kinetics. Results showed low coarsening rates for M23C6 precipitates in the Fe-Cr-C ternary alloy. Interfacial energy of M23C6/ferrite interface is between 0.1 and 0.3 J·m-2 for the coarsening of M23C6 ageing at 780 ℃.

关键词: M23C6 , coarsening , PSD , interfacial energy

Secondary M6C precipitation in K40S cobalt-base alloy

Materials Letters

Secondary M,C precipitation was investigated in K40S cobalt-base alloy after 100 h aging at 950 degreesC. The results showed that it was closely related to the tungsten-rich zones inherited from the as-cast condition and the degeneration of the primary M7C3 carbide. A direct element reaction, 6M + C --> M6C, in which C comes from the decomposition of the M7C3 carbides, is suggested as the mechanism of secondary M6C precipitation in K40S alloy. (C) 2001 Elsevier Science B.V. All rights reserved.

关键词: M6C precipitation;aging;M7C3 carbide;superalloy

MECHANISM OF SECONDARY M_(23)C_6 PRECIPITATION AROUND MC IN A COBALT-BASE SUPERALLOY

W.H. Jiang , X.D. Yao , H.R. Guan and Z.Q. Hu(1) Department of Superalloys , Institute of Metal Research , The Chinese Academy of Sciences , Shenyang 110015 , China2) Department of Metal Materials Engineering , Shenyang Polytechnic University) Shenyang 110023 , China )Manuscript received in revised form 11 September 1998

金属学报(英文版)

Secondary M23C6 precipitation around primary MC carbide in a directionally solidified cobalt-base saperalloy was investigated duriny aging at 850℃. The results show that it was closely related to the decomposition of the MC. Two mechanisms were suggested,i.e. the in situ reaction, MC+γ→M23C6+C, and the direct reaction, M+C→M23C6,in which MC acted as a carbon source.

关键词: cobalt-base superalloy , null , null , null

MAGNETIC PROPERTIES OF Nd_2(Fe_(1-x)M_x)_(14)B(M=C,Si)ALLOYS

XING Feng JIANG Chao HE Wenwang Department of Physics , Peking University , Beijing , China [Originally published in ACTA METALL SIN (CHINESEEDN) 24 (5) 1988pp B348—B352 , received 22 October 1986:in revised form 8 May 1987]

金属学报(英文版)

The magnetic properties of Nd_2(Fe_(1-x)M_x)_(14)B(M=C and Si) compounds have been investi- gated.Substituting Fe by small amount of metalloid C and Si atoms,the compounds are in tetragonal structure and have uniaxial anisotropy.The substitution of C for part of Fe de- creases the Curie temperature of the compounds and the intrinsic coercivity of bond samples at low temperature.The replacement of Fe by Si makes the Curie temperature increase with a maximum at the vicinity of x=0.15.When the range of the content of Si is 0≤x≤0.10,the coercivity distinctly increases at room temperature.from 62.7 kA/m at x=0 to 138.7kA/m at x=0.06,where the residual magnetization has a maximum:in the mean time the saturation magnetization decreases only by a small amount.

关键词: Nd-Fe-B alloy , null , null

Formation and stability of nano-scaled M(23)C(6) carbide in a directionally solidified Ni-base superalloy

Materials Characterization

The precipitation of nano-scaled M(23)C(6) carbide at intragranular regions (especially in dendritic core regions) has been systematically investigated in a directionally solidified Ni-base superalloy. The crystallographic orientation relationship between the M(23)C(6) phase and the gamma matrix phase was found to be (100)(M23C6)//(100)(gamma), [100](M23C6)//[100](gamma). Additionally, M(23)C(6) carbide was very stable during creep and long-term thermal exposure, which makes the fine M(23)C(6) carbide an effective strengthening phase in gamma matrix. (C) 2009 Elsevier Inc. All rights reserved.

关键词: Nano-scaled M(23)C(6);Ni-base superalloy;Creep;Long-term thermal;exposure;annealing twins;precipitation;creep;microstructure;mechanism